AU2007203093A2 - Xylitol dehydrogenase-inactivated and arabinose reductase-inhibited mutant of Candida Tropicalis, method of producing high-yield of xylitol using the same, and xylitol produced thereby - Google Patents

Description

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0 0 Xylitol dehydrogenase-inactivated and arabinose reductase-inhibited mutant of Canda tropicals, method of producing high-yield of xylitol using the same, and xylitol produced thereby BACK=GEOUoth OF THE INVflTION c Field of the Invention 0 C The present invention relates to xylitol dehydrogenaseinactivated and arabinose reductase-inhibited mutant of Candida tropicalls, method of producing high-yield of xylitol using the same, and xylitol produced thereby. More specifically, the present invention relates to a xylitol production method, in which an inconvenience that concentration of dissolved oxygen in a xylitol-producing medium should be maintained at a very low level can.be eliminated through the use of a xylitol dehydrogenaseinactivated mutant of cnadida tropicalis, and the production of byproduct arabitol, which is produced when using a biomass as a substrate and adversely affects the yield of xylitol, can be significantly reduced through the use of Candida tropicalis mutant ara-89 (KCTC 11136bp), having an inhibited activity of .arabinose reductase converting arabinose to arabitol, thus increasing the production of xylitol, as well as xylitol produced by the method.

1 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N.513 D004 ;1 0 0

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C' Description of the Prior Art Xylitol, a five-carbon sugar alcohol, has high Cn sweetening power, and thus is widely used as a functional O 5 sugar substitute for sugar. Because xylitol is found

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0 naturally in a variety of fruits or vegetables in very small amounts, the extraction of xylitol from fruits or vegetables is not industrially advantageous. For this reason, xylitol is produced by a chemical method of reducing a hemicellulose hydrolyzate rich in xylose.

However, in the chemical method, it is difficult to isolate and purify xylose or xylitol from other hydrolyzates occurring in the hemicellulose moiety, a lot of costs are incurred and the yield of xylitol is as low as about 60%. Also, it is a high-temperature and high-pressure employing alkali, which causes problems of risk and waste.

In recent attempts to overcome such shortcoming, biological methods for producing xylitol have been actively studied. Korean Patent Registration No. 1999819 discloses a method of producing xylitol, in which new strain Candida tropicalis is cultured in a medium, containing xylose, a nitrogen source and inorganic salts, to convert xylose to xylitol. Also, PCT International Patent Publication No.

W088/05467 discloses a method of producing xylitol from a high concentration of xylose by culturing Candida 2 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P005 ;1 0 0 -s guillieamondii under conditions employing limited aeration.

i Such biological methods can employ, as a raw material, a relatively low purity of xylose ccmpared to the chemical c methods and are safe and environment-friendly, because the 5 processes themselves are carried out at room temperature 0 and atmospheric. pressure. Thus, studies focused on the o production of xylitol by a variety of bacteria, yeasts, Sfungi and recombinant yeasts have been conducted to produce xylitol in high productivity and high yield (Winkelhausen, EB et al., J. Ferment. Bioeng- 86:1-14, 1998; Granstr6m, T.

B. et al., Appl. Microbiol- Biotechnol. 74:277-281, 2007).

However, bacteria and recombinant yeast strains were not suitable for the production of xylitol, because they showed a weak metabolic activity of producing xylose or low efficiency. However, among yeast strains, Candida sp strains are known as strains suitable for the biological production of xylitol, because they show high xylitol productivity and yield compared to other microorganisms.

According to studies conducted to date, it is known that, as shown in FIG. 1, Candida sp strains, such as C.

guillezmondi, C. parapsilosis and C. tropicalis, convert xylose, absorbed from cells, to xylitol by xylose reductase, and converts xylitol to xylulose by xylitol dehydrogenase. Xylulose is then converted to phosphate by xylulokinase, and xylulose-5 -phosphate is used 3 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 006 0 O0 ;Z for the growth and maintenance of cells through a pentose phosphate pathway (see Laplace, J. M. et al., Appl.

Microbiol. Biotechnol., 36:158-162, 1991; Hahn-Hagerdal, B.

M et al., Enzyme Microb. Technol., 16:933-943, 1994). That O 5 is, xylitol-producing strains use xylose as a carbon source c o for cell growth. Xylitol converted from xylose by xylose reductase is then converted to xylulose by xylitol C dehydrogenase, and in this case, when the aeration of the medium is limited such that the concentration of dissolved oxygen is maintained as .low as intracellular redox imbalance is incurred to reduce the supply of nicotinamide adenine dinucleotide (NAD) as a cofactor required by xylitol dehydrogenase and inhibit the conversion of xylitol to xylulose. As a result, xylitol is accumulated in cells and media, and thus xylitol is produced from xylose in a yield of 60-80%. That is, in the prior technology of producing xylitol using xylitolproducing strains, it is necessary to limit aeration to maintain the concentration of dissolved oxygen at a low level. Thus, studies focused on enhancing the productivity and yield of xylitol by limiting the aeration of medium to maintain the concentration of dissolved oxygen at a low level so as to intentionally induce intracellular redox imbalance have been actively conducted (see Kim, S- Y. et.

4 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P007

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0 0 ci sal, J. Ferment. Bioeng., 83(3):267-270, 1997; Korean C, Patent Publication No. 1996-030577).

Japanese Patent No. 1998276791 discloses a method of r producing xylitol using a concentrated Candida parapsilosis strain at a dissolved oxygen concentration of 0.1-5.0%.

0 However, when xylitol is produced using an industrial scale o fermenter, it is substantially impossible to control the 0 Ci concentration of dissolved oxygen to a low level as described above, and even if the control is possible, the production yield is only about 70-80%. Also, there is processing inconvenience, as Korean Patent Registration No.

10-0259470 suggests an agitation rate for controlling oxygen transfer rate for optimizing xylitol production to microaerobic conditions corresponding to a DOT (percent concentration of oxygen in medium) of less than 1%.

In the light of the above, there is a need to develop to a novel technology that enhances productivity and minimizes the production of byproducts- Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is ccomonly' known by those skilled in the art to which the invention relates, at the priority date of this application.

COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P008 0 0 SSUMMARY OF THE INVENTION

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Accordingly, the present invention has been made in Sorder to solve the above-mentioned problems occurring in the prior art, and it is a first object of the present 0q invention to provide a method for producing a high yield of Sxylitol, which can eliminate the inconvenience that the 0< aeration of medium in a process of producing xylitol using a xylitol-producing strain should be limited to maintain the concentration of dissolved oxygen at a low level..

It is a second object of the present invention to provide a method for producing a high yield of xylitol, which can minimize the production of byproduct. arabitol, which is produced in a process of producing xylitol using a biomass hydrolyzate.

it is a third object of the present invention to provide a method for producing a high yield of xylitol, which can solve the shortcoming in that when a biomass hydrolyzate is used directly as a substrate, xylitol productivity and final xylitol concentration will be low.

To achieve the above objects, in one aspect, the present invention provides a method of producing a high yield of xylitol using a xylitol dehydrogenase-inactivated mutant of Candida tropicalis, the method comprising inoculating and culturing the Candida tropicalis mutant in medium, wherein 6 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 9009 ;1 0 0 C- the culture is carried out under fully aerobic conditions I without a separate process of controlling the concentration of dissolved oxygen in the medium to a low level of 0.5-2%.

c n In the above xylitol production method, the substrate O 5 component is a biaroass hydrolyzate.

0 The xylitol production method is preferably performed Sthrough fed-batch culture using, as a feeding solution, a C mixture of the biomass hydrolyzate and a carbon source.

The biomass hydrolyzate is preferably a corncob bydrolyzate, a sugarcane bagasse hydrolyzate, a coconut byproduct or a hydrolyzate of Betula platyphylla var.

japonica.

The carbon source is preferably glycerol.

Also, in the xylitol production method, the concentration of dissolved oxygen in the culture medium is higher than In another aspect, the present invention provides a xylitol dehydrogenase-inactivated and arabinose reductaseinhibited mutant of Candida tropicalis, and a method of producing a high yield of xylitol using the same. More specifically, the present invention provided Candida tropicalis mutant ara-89 (KCTC 11136bp) having an inhibited activity of arabinose reductase converting arabinose to arabitol, selected from xylitol dehydrogenase-inactivated mutant of Candida tropicalis by treatment with 7 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 D010 0 0 Smethanesulfonic acid ethylester (MS) through random o nmutagenesis, as well as a method of producing a high yield of xylitol using said Candida tropicalis mutant ara-89 S(KCTC 11136bp).

0 O 5 In the xylitol production metbod, the culture of the 0 mutant is preferably carried out under fully aerobic o conditions without a separate process of controlling the 0 concentration of dissolved oxygen to a low level of 0.5-2%, and a biomass hydrolyzate is preferably used as a substrate.

The xylitol production method is preferably performed through fed-batch culture using, as a feeding solution, a mixture of the biomass hydrolyzate and a carbon source.

The biomass hydrolyzate is preferably a corncob hydrolyzate, a sugarcane bagasse hydrolyzate, a coconut byproduct or a hydrolyzate of Betula platyphylla var.

japonica.

The carbon source is preferably glycerol.

Also, in the xylitol production method, the concentration of dissolved oxygen in the culture is higher than In yet another aspect, the present invention provides xylitol produced by any one of the above xylitol production methods.

8 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 011 0 0

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The present invention also includes Candida tropicalis BS-xdhl (KCTC 11137BP) having such a property that xylitol dehydrogenase is inactivated through deletion of xylitol C dehydrogenase gene.

o O The present invention further includes a method of o producing high-yield .of xylitol using the Candida Stropicalis BS-xdhl(KCTC 11137BP).

The present invention also provides Xylitol dehydrogenase-inactivated mutant of tropicalis.

The present invention also provides a method of producing high-yield of xylitol using the same under fully aerobic conditions.

The medium preferably contains a biomass hydrolyzate as a substrate component.

The culture can be performed through fed-batch culture using as a feeding solution a mixture of the biomass hydrolyzate and a carbon source.

The present invention also provides Xylitol produced according to a method set forth in any one of the previous paragraphs.

9 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P012 ;1 0 0 Ci Oc BRIEF DESCRIPTION OF THE DRAWINGS o 5 The above and other objects, features and advantages of 0 the present invention will be more clearly understood from Sthe following detailed description taken in conjunction 0 Ci with the accompanying drawings, in which: FIG. 1 shows xylose and arabinose metabolic pathways by a xylitol-producing strain; FIG. 2 is a genetic map of a pXYL2-Ura3 transformation vector for constructing a xylitol dehydrogenase-inactivated mutant of Candida tropicalis, according to a preferred embodiment of the present invention; and FIG. 3 is a flow chart showing a method of producing xylitol using a Candida tropicalis mutant (KCTC 11136BP) according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the inventive method for producing a high yield of xylitol using a xylitol dehydrogenase-inactivated mutant of Candida tropicalis will be described in detail with reference to the accompanying drawings.

COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 D013 ;1 0 0 FIG. 1 shows xylose and arabinose metabolic pathways by -C a xylitol-producing strain.

FIG. 2 is a genetic map of a pXYL2-Ura3 vector for c n constructing a xylitol dehydrogenase-inactivated mutant of Candida tropicalis, according to a preferred embodiment of C the present invention.

SA process of constructing a Candida tropicalis mutant C lacking the activity of xylitol dehydrogenase and producing xylitol using the constructed mutant is as follows.

When a pXYL2-Tra3 transformation vector is introduced into Candida tropicalis, a xylitol denydrogenase gene is selectively removed through an intracellular mechanism of homologous recombination, and thus a transformed strain, which cannot grow in a medium containing only xylose as a carbon source, can be constructed.

In the xylitol dehydrogenase inactivated mutant of candida tropicalis, because xylitol converted from xylose is no longer used for cell growth, xylose cannot be used as a carbon source, and thus cell growth does not occur. Only when a carbon source such as glycerol or glucose other than xylose is added to medium, cells can grow using the carbon source. Thus, xylose is used only as a substrate for xylitol production, and the carbon source is used to grow cells and supply nicotinamide adenine dinucleotide phosphate-reduced form (NADPH) as a cofactor required by 11 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D014 0 0 xylose reductase. In particular, in the case of the xylitol dehydrogenase-inactivated mutant, because there is no need to induce redox imbalance for the enhancement of M xylitol yield and production, unlike the existing strain, e 5 it was anticipated that the concentration of dissolved 0 oxygen in a culture process would not need to be controlled o to a low level. Also, because yeast strains can use 0 glycerol as a carbon source under aerobic conditions, it was anticipated that, when glycerol is used as a cosubstrate, cell growth rate and NADPH supply rate can be influenced by aeration rate.

Thus, the xylitol dehydrogenase-inactivated mutant of Candida twpicalis was inoculated into a xylitol-producing medium containing xylose, glycerol, yeast extract, KH 2

PO

4 and MgSO 4 7H20, and experiments for producing xylitol in various aeration conditions were carried out. The aeration rate was controlled by the agitation speed of an agitator.

The experimental results showed that xylitol production rate was high when the agitation speed was higher than a given level, that is, when aeration rate was high. This suggests that the assimilation of glycerol in cells is affected by aeration rate, and an increase in aeration rate leads to an increase in the assimilation of glycerol and an increase in the supply rate of NADPH, resulting in an 12 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 9015 ;1

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increase in xylitol productivity. Also, the yield of Cq xylitol from xylose was constant in a range of 97-98% regardless of aeration rate, suggesting that xylitol was produced in a theoretical yield of almost 100%, because n 5 xylitol dehydrogenase activity was eliminated regardless of C intracellular redox imbalance.

o Biomasses, such as corncobs, sugar cane stems, coconut 0 Ci byproducts and Betula platyphylla var. japonica, are rich in hemicelluloses including xylose, arabinose and glucose, and particularly, have a high content of xylose. Thus, hydrolyzates of the biomasses can be used directly for the production of xylitol. In the present invention, xylitol was produced using, as a substrate, a corncob hydrolysate consisting of 83.5% xylose, 5.3% glucose and 11.2% arabinose, and using glycerol as a co-substrate. The xylitol-producing strain consumed all of glucose contained in the hydrolyzate for cell growth and showed a xylitol yield of 97.2% and a xylitol productivity of 3.24 g/L/h.

Moreover, a high concentration of xylitol was produced using fed-batch culture while the concentration of xylose in the medium was maintained at less than 100 g/L, because a high xylose concentration of more than 100 g/L would be unfavorable for cell growth and xylitol production. During the production of xylitol, a mixture of a corncob hydrolyzate as a xylose raw material with glycerol as a 13 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0. 513 P016 ;1 0 0 C carbon source for cell growth and NADPH supply was continuously supplied. As a result, xylitol was produced in a yield of 97% and a productivity of 2.67 g/L/h.

en Glucose contained in the corncob hydrolyzate was completely O 5 consumed during the cell culture process. Also, 15.2 g/L Scorresponding to 57% of the total concentration (26.5 g/L) Sof arabinose added remained as arabinose, and 11.3 g/L C corresponding to 43% was converted to arabitol.

Hereinafter, the inventive method of producing a high yield of xylitol using arabinose reductase-inhibited mutant of Candida tropical s ara-89 (KCTC 11136bp) will be described in detail with reference to the accompanying drawings.

FIG. 3 is a flow chart showing a method of producing xylitol using xylitol dehydrogenase inactivated and arabinose reductase-inhibited mutant of Candida tropicalis (KCTC 11136bp), according to a preferred entodiment of the present invention.

The mutant ara-89 (KCTC l1136bp) having an inhibited activity of arabinose reductase converting arabinose to arabitol was selected from xylitol dehydrogenaseinactivated mutants of Candida tropicalis using, as an alkylating agent, methanesulfonic acid ehtylester (EMS) inducing random mutagenesis. That is, the present inventors have developed a mutant strain in which a 14 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HPLFORD CO 4 62837999 NO.513 3017 ;1 0 0 h- cellular metabolic process of converting arabinose to arabitol was inhibited by mutation to reduce arabitol productivity. The enzymatic activities of the mutant c strain were measured and, as a result, the activity of O 5 xylose reductase converting xylose to xylitol was the same as that of the parent strain, whereas the activity of Sarabonose reductase converting arabinose to arabitol was 0 decreased by 63%.

Also, xylitol production was carried out through fedbatch culture using the mutant strain and, as a result, xylitol was produced in a yield of 97% with a productivity of 2.80 g/L/h. Glucose contained in the corncob hydrolyzate was completely consumed during the culture process. In addition, 23.7 g/L corresponding to 85% of the total amount (27.9 g/1) of arabinose added, remained as arabinose, and 4.2 g/L corresponding to 15% was converted to arabitol.

Hereinafter, the present invention will be described in further detail with reference to examples.

Example 1 To clone unknown Candida tropicalis xylitol dehydrogenase gene, the gene homology between already known Pichia stipitis xylitol dehydrogenase and genes belonging to the medium-chain alcohol dehydrogenase family, including sorbitol dehydrogenase, alcohol dehydrogenase and threonine COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D018 ;1 0 0 dehydrogenase, was investigated. using the resulting highly conserved region as a template, PCR was performed using the following primers (SEQ ID NO: 1 and SEQ IN NO: 2) in the n following conditions to obtain a 1,095-bp Candida 0 C 5 tropicalis xylitol dehydrogenase gene: 1 min at 94 0 C, 0 ci cycles of 30 sec at 94 6C, 30 sec at 58 C and 30 sec at 0 72 and 3 min at 72 The amplified Candida tropicalis xylitol dehydrogenase gene was cloned into a pGEM-T easy vector (BIONEX, Korea), a BamHI site was introduced into the middle of the xylitol dehydrogenase gene, and an ura3 gene was introduced into the introduced BamHI site, thus obtaining a 4.7-kb pXYL2-U'a3 transfoxration vector as shown in FIG. 2.

primer F: 5' -aatggtcttggtcacgaatcc-3' (SEQ ID NO: 1); and primer R: 5'-gctctgaccaagtcgtaggcttc-3' (S.EQ ID NO: 2).

The obtained vector pXYL2-Ura3 was introduced into Candida tropicalis, which was then plated on an Urasildeficient solid screening medium (6.7g/L yeast nitrogen base (amino acid-free), 20 g/L glucose, and 15 g/L agar powder) and incubated at 30 °C for 2 days.

Then, each of the colonies formed on the solid medium was inoculated onto a xylose-containing solid medium (6.7 16 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 C07129 I g/L yeast nitrogen base (amino acid free), 20 g/L xylose, and 15 g/L agar powder) and a glucose-containing solid )medium (6.7 g/L yeast nitrogen base (amino acid free), g/L glucose, and 15 g/L agar powder). Then, they were incubated at 30 OC for 2 days. Then, a strain, which did not grow on the xylose-containing solid medium and grew S only on the glucose-containing solid medium, was selected, Sthus obtaining xylitol dehydrogenase-inactivated mutant of Candida tropicalis.

0 The present inventors performed the following examples using the mutant strain newly selected for use in the present invention, instead of using a mutant strain selected at the time of a previous application (Korean Patent Application No. 10-2005-0079751) relating to said Candida tropicalis mutant strain. In the present invention, the newly selected mutant strain was named "BSxdhl" (Deposit Number: KCTC 11137BP) for convenience of description.

Example 2 The effects of medium aeration and oxygen transfer rate on xylitol yield and productivity in the production of xylitol using the xylitol dehydrogenase-inactivated mutant of Candida tropicalis BS-xdhl were investigated.

29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 I020 ;1 0 0 -s The xylitol dehydrogenase-inactivated mutant of Candida "C tropicalis BS-xdhl was inoculated in 3 ml of YM medium g/L glucose, 3 g/L yeast extract, 3 g/L malt extract, and Sg/L bacto-peptone) and cultured in a shaking incubator at 0 e 5 30 C and 200 rpm for 12 hours. Then, 1 ml of the culture Smedium was inoculated in 50 ml of YM medium and cultured in 0 0 a shaking incubator at 30 "C and 200 rpm for 12 hours.

Then, 50 ml of the culture medium was inoculated in a fermenter containing 1 liter of a xylitol-producing medium (50 g/L xylose, 20 g/L glycerol, 10 g/L yeast extract, g/L KH 2 POa and 0.2 g/L MgSO4-7H20, pH 4.5) and cultured at for 24 hours with agitation at 300, 400 and 500 rpm, and the changes in dry cell weight, xylose, glycerol and xylitol concentrations with the passage of time were measured. Specifically, the dry cell weight was calculated by measuring the absorbance of the sample at 600 nm with a spectrophotometer (Shimadzu, Japan) and converting the measured value using a predetermined standard curve. Also, the sample was centrifuged and the supernatant was analyzed with an HPLC (Shimazu, Japan) system (Sugar-Pak I column (Waters, USA); refractive index detector (Waters, USA); solvent: water; flow rate: 0.5 ml/min; column temperature: to measure the concentrations of xylose, glycerol 18 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P021 ;1 0 0 -C and xylitol, The measurement results are shown in Table 1 below.

[Table 1] SEffects of aeration on xylitol yield and productivity in O 5 the production of xylitol using the xylitol dehydrogenaseinactivated mutant of Candida tropicalis BS-xdhl Agitation speed (pm) STime 300 .400 500 1 h) Xyitol entatia XyWitocaaio~n~ m Xyitaio anmaicn Ai QFA 0 0.0 0.0 0.0 6 1.6 1.9 1.1 12 8.4 13.9 38.3 13.6 35.4 48.4 18 181 49.0 48.4 24 30.4 47.5 48.2 As shown in Table 1, in the case of an agitation speed of 500 rpm corresponding to the highest oxygen transfer rate, 48.4 g/L of xylitol was produced in a culture time of hours, whereas agitation speeds of 400 rpm and 300 rpm showed xylitol productions of 35.4 g/L and 13.6 g/L, respectively, suggesting that xylitol productivity was proportional to agitation speed.. Although not shown in Table above, the production of xylitol was no longer increased at an agitation speed higher than 500 rpm.

Such results suggest that the assimilation rate of glycerol in cells is affected by aeration rate, and until 19 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 3022 0 0 dissolved oxygen is sufficient, an increase in oxygen transfer rate leads to an increase in the assimilation rate of glycerol and an increase in NADPH supply rate, resulting in an increase in xylitol production rate. Also, the production yield of xylitol from xylose was constant in a 0q range of 97-98% independent of aeration rate, suggesting o that xylitol was produced in a theoretical yield of almost 0 Ci 100%, because xylitol dehydrogenase activity was eliminated regardless of intracellular redox imbalance.

Thus, when the xylitol-porducing strain was used to produce xylitol, xylitol could be produced even in high productivity and a theoretical yield of almost 100% in an industrial large-scale fermenter, because there was no need to maintain the dissolved oxygen level as low as 0.5-2.0%- Also, when the yeast strain is cultured in a low-dissolvedoxygen condition, byproducts such as ethanol and glycerol, which reduce xylitol yield and inhibit xylitol purification and crystallization, will be produced, whereas, in the case of the xylitol dehydrogenase gene-disrupted mutant strain, a more efficient process could be constructed, because a high level of dissolved oxygen could be maintained so that byproducts such as ethanol and glycerol were not produced.

Ecample 3 Xylitol was produced using a corncob hydrolyzate as a substrate.

COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62937999 NO.513 P023

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0 0 The xylitol dehydrogenase-inactivated mutant of Candida tropicalis BS-xdh3. was cultured in the same conditions as in Example 2, and 50 ml of the culture medium was inoculated in a fermenter containing 1.0 liter of a xylitol-producing medium (100 g/L xylose, 6.6 g/L glucose, 0 13.4 g/L arabinose, 30 g/L glycerol, 10 g/L yeast extract, g/L 1C 2 P,0 4 and 0.2 g/L MgSO 4 -7H 2 O, pH 4.5) including a corncob hydrolyzate (83.5% xylose, 5.3% glucose and 11.2% arabinose) and was cultured at 30 OC for 30 hours with agitation at 500 rpm. Then, the changes in dry cell weight and xylose, glucose, arabinose, arabitol, glycerol and xylitol concentrations with the passage of time were measured. The measurement of dry cell weight and xylose, glucose, arabinose, arabitol, glycerol and xylitol concentrations was carried out in the same manner as described in Example 2. The measurement results are shown in Table 2 below.

ETable 2] Results of production of sylitol in high yield and high productivity through batch culture using corncob hydrolyzate Dry cel X)4=se Glerol Armabe Aaitol Xylit wdot cncmtion caad=tium cmdikncdio Mcanction ConcaVttion (g1L) (g1L) (gL) (gL) (gL) (gfL) 0 0.2 100.0 30.0 13.4 0.0 0.0 21 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 D024 0 0 ci S6 1.5 100.0 29.8 13.4 0.0 0.0 12 122 96.7 283 122 1.0 3.2 C 18 163 622 18.7 10.8 2.1 35.7 24 15.0 20.9 9.0 9.6 3.1 78.5 152 0.0 23 9.2 3.8 97.2 0 As can be seen from the results in Table 2, the xylitol-producing mutant consumed all of glucose for cell Sgrowth and used glycerol as a co-substrate. Also, xylitol was produced in an amount of 97.2 g/L for 30 hours using, as a substrate, xylose contained in the corncob hydrolyzate in a large amount, and some of arabinose was converted to arabitol. Herein, xylitol yield was 97.2%, and xylitol productivity was 3.24 g/L/h.

In this Example, the xylitol yield was the same as the case of using pure xylose, and the xylitol productivity was similar thereto. Thus, when an inexpensive biomass hydrolyzate rather than pure xylose is used as a substrate for xylitol production, it will be advantageous for increasing the economy of production technology and will be environment-friendly, because biomass waste is recycled.

Example 4 A high concentration of xylitol was produced using fedbatch culture while the xylose concentration in medium was maintained at less than 100 g/L, because a high xylose 22 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO. 513 D025 0 0 Z concentration of more than 100 g/L would interfere with cell growth and xylitol production- The xylitol dehydrogenase-inactivated mutant of Candida M tropicalis BS-xdhl was cultured in the same conditions as in Example 1, and 50 ml of the culture medium was o inoculated in a fermenter containing I liter of a xylitolo producing medium (50 g/L xylose, 3.3 g/L glucose, 6.7 g/L C arabinose, 20 g/L glycerol, 10 g/L yeast extract, 5 g/L KH2POa and 0.2 g/L MgSO 4 -7H20, pH 4.5) prepared using a corncob hydrolyzate and was cultured with shaking at 30 °C and 500 rpm. From 12 hours after the start of the culture, a feeding solution (460 g/L xylose, 30.4 g/L glucose, 61.6 g/L arabinose and 138 g/L glycerol) containing a corncob hydrolyzate was added, and the resulting culture medium was subjected to fed-batch culture for 72 hours while the xylose concentration in the medium was controlled to less than 100 g/L. The changes in dry cell weight and xylose, glucose, arabinose, arabitol, glycerol and xylitol concentrations with the passage of time were measured in the same manner as described in Example 2. The measurement results are shown in Table 3 below.

[Table 3] 23 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 P026

;Z

Results of production of rylitol in high yield and high productivity through fed-batch culture using corncob hydrolyzate Dr Xyse Gycal Ax*ee Ambital XWitl Time Dry odICfii~i8ca iam onestain cmcrafim cncenraim camnciraki wet (gL) o9 vg (L (1L) 9L) O o 0.6 50.0 20.0 6.7 0.0 0.0 12 17.5 24.5 7.5 53 1.0 24.5 24 261 29.8 13.1 11.8 5.3 92.5 36 30.8 29.0 9.9 14.4 7.5 1342 48 28.4 132 4.0 11.8 9.1 1603 30A 175 1.7 13.6 9.9 175.0 72 30.8 21.9 6.7 15.2 11.3 1923 As can be seen from the results in Table when the production of xylitol was pertonned through fed-batch culture using a corncob hydrolyzate, xylitol was produced in a concentration of 192.3 g/L for 72 hours, indicating a xylitol yield of 97% and a xilytol productivity of 2.67 g/L/h. Glucose contained in the corncob hydrolyzate was cowpletely consumed during the cell culture process, and 15.2 g/L corresponding to 57% of the total amount (26.5 g/l) of arabinose added remained as arabinose, and 11.3 g/L corresponding to 43% was converted to arabitol. Herein, the concentration of arabitol was 11.3 g/L, and the concentration of final xylitol concentration to arabitol concentration was 100:5.9.

24 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D027 ;1 0 0 -s Because the xylose reductase of yeast strains also has ^C arabinose reductase activity, arabinose contained in biomass hydrolyzates can be inevitably converted to c arabitol. Arabitol, a five-carbon sugar alcohol like 5 xylitol, is a byproduct, which has a molecular structure 0 and physical properties, similar to those of xylitol, and Sthus interferes with purification and crystallization 0 Ci processes in xylitol production so as to reduce xylitol production yield. When bicaass hydrolyzates as inexpensive xylose sources are used for the production of xylose, a given amount of arabitol will be produced, and when the amount thereof is higher than a given concentration, it will reduce xylitol production yield. For this reason, it is required to inhibit arabitol production.

Example On the basis of the results of Example 4, a novel xylitol-producing strain, in which a cellular metabolic process of converting arabinose to arabitol was inhibited, was developed from the xylitol dehydrogenase-inactivated nmtant of Candida ttrpicalis BS-xdhl using methanesulfonic acid ethylester (EMS) as an alkylating agent.

For this purpose, the xylitol dehydrogenase-inactivated mutant of Candida tropicalis BS-xdhl was inoculated in 3 ml of YM medium (20 g/L glucose, 3 g/L yeast extract, 3 g/L malt extract and 5 g/L of bacto-peptone 5g/L) and was COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P028 0 0 cultured at 30 OC for 24 hours with shaking at 200 rpm.

Then, 30 ml of the culture medium was transferred into a conical tube, and then the cells were washed two times with 30 ml of minimal A buffer (10.5 g/L K 2 HP0 4 g/L KR 2

PO

4 1.0 g/L (MN4) 2 S0 4 and 0.5 g/L sodium citratey.

The cells were resuspended in 15 ml of minimal A buffer, 0 0 and 450 Fl of methanesulfonic acid ethylester (WMS) was then added thereto.

Then, the cells were incubated with shaking at 30 °C and 200 rpm for 90 minutes. Then, the cells were washed two times with 5 nml of minimal A buffer, resuspended in 2 ml of minimal A buffer and then dispensed on YM agar plate.

Then, the cells were cultured at 30 OC for 2 days, and the resulting single colonies were inoculated and cultured in an arabitol-producing medium (20 g/L arabinose, 20 g/L glycerol and 10 g/L yeast extract) for 24 hours- The concentrations of arabitol produced by the mutant strains were quantified using the HPLC analysis method described in Example 2, and mutant strains showing an arabitol production, which was 50% lower than that of the original strain, were selected. Rach of these mutant strains was inoculated in 5 ml of a xylitol-producing medium (20 g/L xylose, 20 g/L glycerol and 10 g/L yeast 26 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D029 0 0

(N

extract) and cultured for 24 hours, and mutants strains showing a xylitol concentration, which was higher than of that of the parent strain, were finally selected. The Cselection results are shown in Table 4 below.

[Table 41 o Selection of mutants showing inhibited arabitol production o Man Dlrycelweigt Arabol ccmcatrai Xyital owocetaion Ssias (gL) Paratstain 5.5 39 19.7 ara-06 4.9 1.9 16.6 aa-26 5.1 1.8 17.9 aa-51 3.9 1.3 15.4 ara-77 5.1 1.7 1&1 aa-89 53 1.7 19.6 AS can be seen in Table 4, in the case of mutant strain 'ara-89', cell growth and xylitol concentration were almost similar to those of the parent strain as a control group, but arabitol concentration was. decreased by compared to the parent strain. To measure the enzymatic activity of mutant strain ara-89, the cells were inoculated and cultured in 50 ml of arabitol-producing medium (20 g/L arabinose, 20 g/L glycerol and 10 g/L yeast extract) for 12 hours, and then resuspended in 50 mM potassium phosphate buffer. Then, the suspension was sonicated five times for seconds for each time to disrupt the cells. Then, the 27 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 9030 suspension was centrifuged and the supernatant was transferred into a 1.5-ml tube. The activity of each of xylose reductase and arabinose reductase was measured using a crude enzyme, 0.2 mM NADPH as a cofactor, and xylose or arabinose as a substrate. Herein, the enzymatic activity was analyzed by measuring the change in absorbance at 340 nm with a spectrophotometer (Shimadzu, Japan). The analysis results are shown in Table 5 below.

[Table Analysis of xylose and arabinose reductase activities of mutant showing inhibited arabitol production xyloseredwuraseactviy(mi) Aratrnasemrucaseacdvity(m) stran Paretsrain 3249 354.7 wa-89 3175 1312 As can be seen in the results in Table 5, in the case of mutant strain ara-89, the activity of xylose reductase converting xylose to xylitol was equal to that of the parent strain, whereas the activity of arabinose converting arabinose to arabitol was decreased by 63%.

The finally selected C. tropicalis mutant ara-89 having an inhibited activity of arabinose reductase was deposited in KCTC (Korean Collection for Type Cultures), an international depository authority for microorganisms, on June 12, 2007 (Accession No. KCTC 11136bp).

28 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 P031 ;1 0 0 Example 6 The mutant ara-89 (KCTC 11136bp) showing inhibited arabitol production was inoculated into 3 ml of YM medium M (20 g/L glucose, 3 g/L yeast extract, 3 g/L malt extract O 5 and bacto-5g/L peptone) and cultured in a shaking incubator Cc Cq at 30 "C and 200 rpm for 12 hours. Then, 1 ml of the Sculture medium was inoculated again into 50 ml of YM medium ci and cultured in a shaking incubator at 30 'C and 200 rpm for 12 hours.

Then, 50 ml of the culture medium was inoculated in a fermenter containing 1 liter of a xylitol-producing medium g/L xylose, 3.3 g/L glucose, 6.7 g/L arabinose, 20 g/L glycerol, 10 g/L yeast extract, 5 g/L EH 2

PO

4 and 0.2 g/L MgSO47Ha0O 0.2g/L, pH 4.5) including a corncob hydrolyzate and was cultured with agitation at 30 "C and 500 rpm. From 12 hours after the start of the culture, a feeding solution (460 g/L xylose, 30.4 g/L glucose, 61.6 g/L arabinose and 138 g/L glycerol) containing a hydrolyzate was added to the medium, and the resulting culture medium was subjected to fed-batch culture for 72 hours while the xylose concentration in the medium was controlled to less than 100 g/L. The changes in dry cell weight and xylose, glucose, arabinose, arabitol, glycerol and xylitol concentrations 29 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 P032 ;1 0 0 Swith the passage of time were measured in the same manner C1 as described in Example 2. The measurement results are shown in Table 6 below.

a [Table 6] Results of production of xylitol through fed-batch ci culture using C. tropicalis mutant ara-89 (KCTC 11136bp) o showing inhibited arabitol production SXylose Glyc ol Aabinose Aabitol Xytol C( Time 1LDry dwel ht cwwatim nr .cai m Drcycllwe iot cncaion cona acatration concansm catratio )1 L)

(PL)

0 0.7 50.0 20.0 6.7 0.0 0.0 12 163 26.1 92 55 02 22.7 24 25.1 28.1 125 12.8 13 90.9 36 28.7 26.0 10.4 16.4 1.9 137.6 48 28.9 122 85 184 2.4 1695 29.1 135 7.6 202 3,0 175.0 72 29.0 5.8 33 23.7 42 2013 As can be seen from the results in Table 6, when the production of xylitol was performed through fed-batch culture using the new mutant strain, xylitol was produced for 72 hours was produced in a concentration of 201.3 g/L for 72 hours, suggesting a xylitol yield of 97% and a xylitol productivity of 2.80 g/L/h. Glucose contained in the corncob hydrolyzate was completely consumed during the cell culture process, and 23.7 g/L corresponding to 85% of the total amount (27.9 g/1) of arabinose added remained as arabinose, and 4.2 g/L corresponding to 15% was converted COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 3033 ;1 0 0

(N

Sto arabitol. Herein, the concentration of final xylitol C, concentration (201.3 g/L) to arabitol concentration (4.2 g/L) was 100:2-1, resulting from a decrease arabitol c production of 65% compared to the parent strain.

O 5 Also, xylitol productivity was increased by 5% compared 0 to the parent strain, suggesting that NADPH required for arabitol production was additionally used for xylitol C production in an amount corresponding to the amont of inhibited arabitol production. As described above, using the newly developed xylitol-producing mutant having an inhibited activity of arabinose reductase, it was possible to ccmplete an efficient process of producing xylitol in high yield and high productivity, in which the production of byproduct arabitol interfering with xylitol purification and crystallization was significantly inhibited.

Example 7 The mutant ara-89 (KCTC 11136bp) showing inhibited arabitol production was inoculated into 3 ml of YM medium g/L glucose, 3 g/L yeast extract, 3 g/L malt extract and 5 g/L bacto-peptone) and culture in a shaking incubator at 30 OC and 200 rpm for 12 hours. Then, 1 ml of the culture medium was inoculated into 50 ml of YM medium and cultured in a shaking incubator at 30 °C and 200 rpn for 12 hours.

31 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D034 ;1 0 0 h- Then, 50 ml of the culture medium was inoculated in a fermenter containing 1 liter of a xylitol-producing medium g/L xylose, 5.2 g/L glucose, 3.8 g/L arabinose, 20 g/L n glycerol, 10 g/L yeast extract, 5 g/L KH 2

PO

4 and 0.2g/L 0 MgSO47H20, pH 4.5) including a sugarcane bagasse ci o hydrolyzate and was cultured with agitation at 30 "C and 0 Ci 500 rpn. The level of dissolved oxygen in the culture process was preferably maintained at more than From 9 hours after the start of the culture, a feeding solution (460 g/L xylose, 30.4 g/L glucose, 61.6 g/L arabinose and 138 g/L glycerol) prepared using hydrolyzates was added to the medium, and the resulting culture medium was subjected to fed-batch culture for 72 hours while the xylose concentration in the medium was controlled to less than 100 g/L. The changes in dry cell weight and xylose, glucose, arabinose, arabitol, glycerol and xylitol concentrations with the passage of time were measured in the same manner as described in Example 2. The measurement results are shown in Table 7 below.

[Table 7] Results of production of xylitol through fed-batch culture using C. tropicallis mutant ara-89 (KCTC 11136bp), showing inhibited arabitol production, and sugar cane bagasse hydrolyzate 32 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D035 Xylose Glyceol Arainose Araitol Xyl3ta Time Dry cel weisgb cmianoticon concItraftimo ocarcaion conceUatrion caocetafion S(g( (gL) (L) 0 0.9 50.0 20.0 3.8 0.0 0.0 12 21.0 523 18.8 4.1 0.0 15.4 24 289 573 16.7 6.7 0.7 845 36 31.4 38.0 13.1 8.8 1.2 1289 48 32.1 17.6 10.5 111 1.7 168.8 32.0 95 72 12.8 19 181.4 72 31.8 3.4 5.5 13.9 21 2032 AS can be seen from the results in Table 7, when the production of xylitol was performed through fed-batch culture using the new mutant strain, xylitol was produced for 72 hours was produced in a concentration of 203.2 g/L of 72 hours, suggesting a xylitol yield of 97% and a xylitol productivity of 2.82 g/L/h. Glucose, the component of the sugarcane bagasse hydrolyzate, was completely consumed during the cell culture process, and 13.9 g/L corresponding to 87% of the total amount (16.0 g/1) of arabinose added remained as arabinose, and 2.1 g/L corresponding to 11% was converted to arabitol. The concentration of final xylitol concentration (203.2 g/L) to arabitol concentration (2.1 g/L) was 100:1.0.

Also, the sugarcane bagasse hydrolyzate had an arabinose content lower than the corncob hydrolyzate by 43%, leading to a decrease in arabitol production of In addition, it had a high glucose content compared to the 33 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D036 ;1 0 0 C' corncob hydrolyzate, leading to a decrease in carbon source Ci glycerol, thus reducing production cost.

AS described above, according to the present invention, xylitol dehydrogenase-inactivated and arabionose reductasee 5 inhibited mutant of Candida tropicalis is used in xylitol 0 production, and thus an efficient xylitol production o process with high yield and high productivity can be Ci achieved by inhibiting xylitol-to-xylulose conversion, inhibiting the production of byproduct arabitol, using a biomass hydrolyzate and also using fed-batch culture.

Also, according to the present invention, because there is no need to control dissolved oxygen concentration to a low level through limited aeration, which was essential in the prior xylitol production method using microorganisms, an economic, safe and environment-friendly xylitol production process can be provided.

AS described above, according to the inventive method of producing xylitol using the Candida tropicalis mutant BS-xdhl lacking xylitol dehydrogenase activity, the use of the Candida tropicalis mutant BS-xdhl eliminates a need to maintain a very low concentration of dissolved oxygen in medium.

Also, according to the present invention, the production of byproduct arabitol from arabinose contained in biomass hydrolyzates can be inhibited through the use of the 34 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 0037 0 0 SCandida tropicalis mutant ara-89 (KCTC 11136bp) having an inhibited activity of arabinose reductase, thus enhancing xylitol productivity.

C Furthermore, according to the inventive xylitol 01 0 5 dehydrogenase-inactivated and arabinose reductase-inhibited

C

o mutant of Candida tropicalis, and the inventive method of a o' high yield of xylitol using the same, the production cost C of xylitol can be reduced through the use of inexpensive biomass hydrolyzates containing a high concentration of xylose.

In addition, xylitol productivity and final xylitol concentration can be enhanced through the use of biomass hydrolyzates and the fed-batch culture process in which a xylose substrate and a carbon source for cell growth are distinguished from each other.

Where ever it is used, the word "camprising" is to be understood in its "open" sense, that is, in the sense of "including', and thus not limited to its "closed" sense, that is the sense of "consisting only of". A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO. 513 9038 from the text. All of these different combinations ci constitute various alternative aspects of the invention.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art 0 that the present invention nay be embodied in other 0q specific forms without departing from the essential o characteristics thereof. The present embodiments and ci examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

36 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29

Claims (13)

1. 3. A method for producing a high yield of xylitol, the method comprising inoculating and culturing a xylitol debydrogenase-inactivated mutant of Candida tropicalis BS- xdhl in medium, wherein the culture is carried out in fully aerobic conditions without a separate process of controlling dissolved oxygen concentration to a low level of 0.5-2%.
2. 4. The method of Claim 3, wherein the medium contains a biomass hydrolyzate as a substrate component.
3. 5. The method of Claim 3, wherein the culture is performed through fed-batch culture using, as a feeding solution, a mixture of the biomass hydrolyzate and a carbon source. 37 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 NO.513 D040 ;1 0 0
4. 6. The method of Claim 4 or 5, wherein the biomass j hydrolyzate is a corncob hydrolyzate, a sugarcane bagasse hydrolyzate, a coconut byproduct or a hydrolyzate of Betula platyphylla var. japonica. 0 7. The method of Claim 5, wherein the carbon source is o glycerol.
5. 8. The method of any one of Claims 3 to 7, wherein the concentration of dissolved oxygen during the culture is higher than
6. 9. A arabinose reductase-inhibited mutant of Cfndida tropicalis ara-89 (KCTC 11136bp), selected from xylitol dehydrogenase-inactivated mutant of Candida tzopicalis BS- xdhl by treatment with methanesulfonic acid ethylester (EMS) through random mutagenesis. A method of producing a high yield of xylitol using the Candida tropicalis mutant ara-89 (KCTC 1136bp) of Claim 7.
7. 11. The method of Claim 10, which comprises culturing the mutant under fully aerobic conditions without a separate process of controlling dissolved oxygen 38 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 1041 0 0 Sconcentration to a low level of in which the culture is carried out using a biomass hydrolyzate as a substrate- e 5 12. The method of Claim 11, wherein the culture is 0 performed through fed-batch culture using, as a feeding Ssolution, a mixture of the biomass hydrolyzate and a carton 0 source.
8. 13. The method of Claim 11 or 12, wherein the biomass hydrolyzate is a corncob hydrolyzate, a sugarcane bagasse hydrolyzate, a coconut byproduct or a hydrolyzate of Betula platyphylla var. japonica.
9. 14. The method of Claim 12, wherein the carbon source is glycerol. The method of any one of Claims 11 to 14, wherein the concentration of dissolved oxygen in the culture is higher than
10. 16. A method for producing a high yield of xylitol being substantially as hereinbefore described with reference to the above described examples and figures of the drawings. 39 COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29 29/06/2007 22:23 HALFORD CO 4 62837999 N0.513 D042 ;1 0 0 h- 17. Xylitol produced according to a method set forth in C any one of Claims 2 to 8 and 10 to 16.
11. 18. Xylitol dehydrogenase -inactivated mutant of n tropicalis. O 5 19. Method of producing high-yield of xylitol using the 0 same under fully aerobic conditions. The method of claim 19, wherein the medium contains c a biomass hydrolyzate as a substrate component.
12. 21. The method of claim 20, wherein the culture is performed through fed-batch culture using as a feeding solution a mixture of the biomass hydrolyzate and a carbon source.
13. 22. xylitol produced according to a method set forth in any one of claims 19 to 21. COMS ID No: SBMI-07973456 Received by IP Australia: Time 21:33 Date 2007-06-29