NL8102157A - PROCESS FOR PREPARING L-AMINO ACIDS BY CAPTURED MICROORGANISMS AND FOAM TO BE USED THEREOF - Google Patents

Description

* -t 4 - 1 -

Process for the preparation of L-amino acids by established micro-organisms and foam to be used therewith.

Various methods of preparing L-amino acids by enzymatic action on appropriate substrates are known. For example, L-alanine can be prepared by growing an L-aspartic decarboxylase-forming microorganism in a nutrient medium and adding L-aspartic acid to the culture fluid (Japanese Patent Publication No. 7560/1971). L-alanine can also be prepared by isolating aspartate decarboxylase from a microorganism and allowing the enzyme to act on L-aspartate, see Biochimica et Biophysica Acta, 67_ (1963). L-Asparinic acid can be prepared by similar methods, see, for example, U.S. Pat. Nos. 2,927,057, 2,971,890, 3,198,712, 3,214,345, 3,310,475, 3,999,586, 4,013,508, and 4,048,018 , British Patent 880,234 and Canadian Patent 697,310. U.S. Pat. No. 3,214,345 employs E. coli cells to prepare L-aspartic acid from ammonium fumarate. However, these methods have the drawback that the resulting L-amino acid is contaminated either with enzyme or with the microbe cells and the food sources, etc. To recover high purity L-amino acid, 20 additional operations are required to remove the enzyme and the other admixtures. Often the reaction mixture is boiled and / or acidified after the reaction is complete to precipitate the enzyme or microorganisms, after which it is filtered.

Then the enzyme or microorganisms can be used only once.

To overcome these drawbacks, it has been proposed to encapsulate microorganisms in polymeric supports; see U.S. Pat. Nos. 3,898,128 and 3,458,400, which encapsulate semipermeable polyaerylamide membranes and the enzymatic conversion of L-aspartic acid to L-alanine using Pseudomonas dacunhae or Achromobacter pestifer, respectively, 8102157 • / r ^: i The Japanese patent publication 6870/1970 discloses the binding of aspartase to an anion exchange polysaccharide. According to Japanese patent publication 17.587 / 1970, polyacrylates are used for encapsulating aspartase forms. 5 micro-organisms, for the preparation of L-aspartic acid.

U.S. patents 3,649,457, 3,791,926 and 3,898,128 are also of interest in this regard. The use of carrageenan as a carrier has been described by Sato in Biochemica et Biophysica Acta 570 (1979), 179-186. Russian patent publications SU 10 423.976 and SU 451.483 describe the recording of E. coli cells in polyacrylamide and the preparation of L-aspartic acid from ammonium fumarate.

Encapsulation of microorganisms in hydrophilic polyurethane foams has also been suggested before, see U.S. Patent 3,905,923. Binding of enzymes to polyurethanes is also described in U.S. Pat. No. 3,672,955, see column 5, lines 27-35. U.S. Patent 4,000,040 discloses the preparation of L-aspartic acid from substrates other than fumaric acid, namely acetic acid, ethanol, and carbohydrates. Hydrophilic polymers have also been used as carriers for chemicals, including bacteriostats and fungicides; see U.S. Patent 3,975,350. It is also known to capture bacterial cells in hydrophobic polyurethanes, see Example 4 of British Patent 953,414.

Another relevant reference is to the article by Sonomoto .. et al in Agric. Biol. Chem. 44 (1980) 1119-1126, according to which steroid conversions are achieved with bacterial cells enclosed in polyurethanes prepared from prepolymers. Fukui et al, in Biochemistry 62, 30 (1980), 381-386, disclose the use of enzymes captured in photo-crosslinkable prepolymers and urethane prepolymers to prepare L-amino acids. Capturing bacterial cells using urethane prepolymers has also been described. In a recent Gordon Research Conference of 11-15 au-35 gustus 1980, the capture of whole cells (especially of genetically engineered E. coli which made very high amounts of penicillin amidase 8102157 * - 3) in urethane prepolymers; biological systems for preparing L-serine and L-tryptophan were also "still under evaluation".

According to the invention, a hydrophilic polyether-polyurethane foam is used in which at least 50 mol% of the alkylene oxide units of the polyurethane are ethylene oxide, with an immobilized L-amino acid-forming microorganism in said foam. By "L-amino acid-forming microorganism" is meant here microorganisms that convert that substrate into an L-amino acid upon contact with a substrate. The invention concerns both organisms which form the appropriate enzymes intracellularly and those which form these enzymes extracellularly. A specific example of the invention is the conversion of L-aspartic acid (here more a substrate than a product) to L-alanine, as will be described further. The invention also relates to a method of preparing the foam and its use for the preparation of L-amino acids.

Preferably, the polyether segments of the polyurethane comprise at least 90 mol% ethylene oxide-20 units. Depending on the amount of crosslinker used, the foam can be both rigid and flexible.The weight ratio between polyurethane and microorganism (based on dry weight) should be between 1:10 and 10: 1, preferably between 2: 1 and 4: 1.

Before mixing the culture with the prepolymer, the dry weight of microorganisms of the culture can be determined by evaporating a sample to dryness at a suitable temperature (eg 50 ° C). Then 50 to 90% of the micro-organisms can be stored in the foam.

Some washout of the cells has been observed in freshly prepared foams, but usually less than 15% thereof.

Generally, the washability increases with the concentration of microbe cells in the final product. There is also more washing out if the microbes contain clogs or lumps, or if you do not mix well.

By "recorded" here is meant that the microorganisms remain in the foam on contact with water or an aqueous solution 8102 157 4 * if - 4 - and cannot be washed out. It is believed that this capture is accomplished by encapsulating the microorganisms in the foam. It is also likely that bonding occurs during barge formation by reacting the isocyanate groups of the polymer with certain groups (eg, amino groups) on the surface of the microorganisms.

The foams are prepared by directly mixing a culture of the L-amino acid-forming microorganism with a urethane prepolymer in the presence of enough water to promote foaming. Generally, the water comes along with the microbe culture, i.e. these cultures usually contain 10 to 90% by weight of water (which can be easily determined by evaporating a sample thereof to dryness). Due to the presence of the water, the prepolymer will foam and at the same time the microorganisms will be captured in it. To do this as best as possible, the pH of the culture should be between 4 and 11, preferably close to 7. During capture, the prepolymer / water weight ratio is generally between 2 r 1 20 and 1: 2, at preferably between "3: 2 and 2: 3, which water is provided by the culture or by a combination of the culture with water added before or during mixing.

After mixing, the foaming is generally completed in 5-10 and the foam cures to its final state in an additional 5-10 minutes. But with large amounts of foam, it is conceivable that you need a little more time.

L-amino acids which can be prepared with the foams according to the invention, and the types to be used therein (which must be recorded) and the substrate are listed in the table below.

8102 157 * - 5 - L-amino acid Microorganism Substrate L-alanine Pseudomonas dacunhae L-aspartic acid (ATCC 21192) L-alanine Alcaligenes faecalis L-aspartic acid 5 (ATCC 25094) L-histidine Brevibacterium imidazolyl-pyrothiogenitalis40 acid) L-histidine Corynebacterium glucose 10 glutamicum (ATCC 21604 and ATCC 21607) L-histidine 1) Brevibacterium flavum 1) glucose (ATCC 21319) 15 2) Glutamic acid former 2) histidinol (eg Comebacterium or Brevibacterium, such as Brevibacterium flavum, ATCC 14067 ) 20 L-isoleucine Serratia marcescens glucose (ATCC 21740) L-isoleucine Serratia marcescens glucose (ATCC 21741) L-isoleucine Serratia larcescens glucose 25 (ATCC 21810) L-isoleucine Brevibacterium hydroxybutyric acid thiogenitalis (ATCC 19240) L-isoleucine breto -8-methyl- 30 thiogenitalis n-valeric acid (ATCC 19240) L-leucine Brevibacterium a-keto-isocapronthiogenitalic acid (ATCC 19240) 35 L-leucine Brevibacterium glucose thiogenitalis (ATCC 19240) L-serine M icrobacterium spec. glycine / form- (ATCC 21376) aldehyde 40 L-serine Nocardia butanica glycine / form- (ATCC 21197) aldehyde L-serine Corynebacterium glycine / form-glycinophilum aldehyde (ATCC 21341) 45 L-theonine Brevibacterium flavum glucose (ATCC 21267) 8 Λ *

V

- 6 -. Continuation of table L-amino acid Micro-organisms Substrate L-theonine Corynebacterium glucose acetoacidophilum 5 (ATCC 21270) L-theonine E. coli (ATCC 13070) glucose L-proline Cornebacterium glucose glutamicum (ATCC 19223) 10 L-proline Microbacterium glucose ammoniaphilum (ATCC 15354 ) L-proline Brevibacterium glucose 15 ammonioagenes (ATCC 13746) L-arginine Bacillus subtilus glucose (ATCC 21742) L-arginine Brevibacterium flavum glucose 20 (ATCC 21742) L-arginine Corynebacterium glucose glutamicum (ATCC 21659) L-tryptofan Brevibacterium g-indoly - 25 thiogenitalis grape acid (ATCC 19240) L-tryptophan Proteus rettgerii indole + pyrodrui- (Ajinomoto.) Venic acid (or serine) (AJ 2770) 30 L-tryptophan E. coli (ATCC 27553) indole + pyruvic acid (or serine) L-tryptophan E. coli (ATCC 8724) indole + pyruvic acid (or serine) L-phenylalanine Brevibacterium phenylpyrodruthiogenitalis venic acid (ATCC 19240) L-phenylalanine Khodosporidium trans-cinnamic acid toruloides CATCC 10788) * 40 L-tyros iné Brevibacterium hydroxyphenylthiogenitalis pyruvic acid (ATCC 19240) L-tyrosine Erwinia herbicola phenol + pyro- (ATCC 21434) grape acid 8102 157 »- 7 -

Continuation of table L-amino acid Microorganisms Substrate L-tyrosine Erwinia herbicola phenol + pyro- (ATCC 21433) grape acid 5 L-lysine Brevibacterium flavum glucose (ATCC 21127-21129) L-lysine Corynebacterium glucose glutamicum (ATCC 13826) 10 L-lysine Coryn glucose glutamicum (ATCC 13827) L-lysine Bacillus megaterium glucose (ATCC 21209) All these microorganisms are publicly available from the aforementioned official tribal collections. However, it should be noted that the present invention is not limited to these examples.

The L-amino acid can be prepared by contacting foam with an aqueous substrate solution and incubating the whole at 15-60 ° C with stirring until the reaction is complete. Then the foam is separated again and can be stored in the refrigerator for next use. The L-amino acid can be separated from the solution in the usual manner.

Otherwise, the enzymatic reaction can be continuous, using a column. For example, the foam is stacked to a kdbm of such density that the water can continue to flow through it. The substrate solution 30 having a pH between 3 and 11 is passed through the column at an appropriate flow rate at a temperature between 15 ° and 60 ° C. An aqueous solution of the desired L-amino acid is obtained as an effluent. This solution can be recycled if desired.

For the preparation of the polyurethane foam 35 8102157 O *. *,: ** * · · '- 8 -. · · · · ·' Suitable prepolymers are obtained by reacting a polyoxyalkylene polyol with an excess of polyisocyanate such as | toluene diisocyanate. That polyol should have a molecular weight of between 200 and 20,000, preferably between 600 and 6,000, and per liter 5 molecule from 2 to 8 hydroxy groups. If foams are made from prepolymers with a functionality of about 2, the final pro essentially unbranched, they have less tensile strength than if they were cross-linked. It is therefore preferable to start from a polyol with more than two functional groups! 10 per molecule; ' these can be obtained by starting from mixing! requirement of diols with triplets or polyols with even higher functionality.

Examples of suitable polyols are (A) essentially unbranched polyols created by reacting ethylene oxide with an initiator such as glycol. Mixtures of ethylene oxide with other alkylene oxides can also be used as long as ethylene oxide thereof is at least 50 mole percent. If the i ·.

unbranched polyethers mixtures of ethylene oxide with, for example! propylene oxide, the order within the polymer chains can be arbitrary as well as blockwise, and the end groups can be so. hydroxoxyethoxy as hydroxypropoxy. A second class of! polyols (B) are those with three or more hydroxy groups per mol. cellular; these are usually formed by reacting alkylene oxides with a polyvalent initiator such as trimethylolpropane, pentaerythritol, etc. In forming a polyol B, the alkylene oxide used may be ethylene oxide or a mixture thereof with other alkylene oxides. Other suitable polyols i (C) are branched or unbranched polyols as listed at A and B together with an initiator or crosslinker; an example of this is a mixture of polyethylene glycol (MG ca 1000) with trimethylolpropane, trimethylolethane or glycerol. This mixture can be left react with excess polyisocyanate so that one can useful polymer, but it is also possible to obtain the Let branched or unbranched polyols react separately with excess polyisocyanate. The initiator, for example trimethylol-1 propane, can also be reacted separately with the polyisocyanate 8102 157. · ". * »: ____ - 9 - be brought. Finally, the separately prepared products are combined with each other to form the prepolymer.

Suitable polyisocyanates and initiators are described in U.S. Patent 3,903,232. The initiators are generally water-soluble or dispersible crosslinkers described in that patent.

Prepolymer A is prepared by combining two equivalents of polyethylene glycol with a molecular weight of about 1000 with 0.6 equivalents of trimethylolpropane. To remove water, the mixture is dried at 100-110 ° C at a pressure of 5-15 torr. This dry mixture is then slowly added over an hour to a vessel containing 5.7 moles of toluene diisocyanate with stirring. Stirring is then continued at 60 ° C for 3 hours. Finally, 0.92 mole of toluene diisocyanate is added over an hour under stirring at 60 ° C. They eventually use an excess of 5% isocyanate and all end groups are now isocyanate, not hydroxyl; the chains have now also become a bit longer.

Example I

A suspension of cells from Alcaligenes fae-20 calis (ATCC 25094) was mixed with 5 g prepolymer A. 8 g of bacteria, containing 1 g of dry matter, were used. The water in this cell mass produced a flexible hydrophilic polyurethane foam in about 15 minutes. The cells were encapsulated within or bonded to the polyurethane matrix.

Example II

The foam obtained in Example I was stacked into a column in a glass tube closed at both ends with a Millipore filter. At the bottom, this column was contacted with 50 g of L-aspartic acid in a storage vessel. Then a solution of 40 ml of ammonia and 10 ml

Tween 80, the pH of which was adjusted to 10 with 50% H 2 PO 4, was passed upward through the column via the aspartic acid. The temperature was about 25 ° C and the flow rate about 0.67 ml / min. During the first 40 hours, the column gave about 0.90 mg / ml (i.e. 0.60 mg / 35 min.) Of L-alanine. He then gave at a flow rate of 0.34 ml / min.

1.62 mg / ml and at a flow rate of 0.17 ml / min. a yield of 8102,157

IV

- 10 - 2.66 mg / ml L-alanine.

The L-alanine was determined using a Technicon Autoanalyzer and an L-amino acid oxidase to convert L-alanine into the corresponding 5-α-keto acid, and the presence of peroxidase is affected. from radish with 2,4-dichlorophenol and

4-aminoantipyrene react to give a quinonimine dye which can be measured colorimetrically at 505 nm. Example III

A column of the particulate foam prepared in Example 1 was packed into a water-jacketed tube. The temperature was adjusted to different values and the substrate was run at a flow rate of 0.67 ml / min. forwarded. The substrate consisted of a solution of 10 ml of concentrated ammonia and 2.5 ml of Tween 80 in 500 ml of deionized water and 53 g of solid L-aspartic acid at room temperature. As the column passed, the substrate was warmed to 27 ° C and then cooled back to room temperature before returning to the storage vessel containing the solid L-aspartic acid; thus an equilibrium solution thereof entered the column. The substrate was continuously recycled through column, cooling coil and storage vessel. This happened at three different temperatures, for 20 hours at 27 ° C, 72 hours at 37 ° C, and about 34 hours at 50 ° C.

The conversions in L-alanine were 112.5 mg / hour (at 27 ° C), 334 mg / hour (at 37 ° C) and 0 mg / hour (at 50 ° C).

Example IV

A culture of Pseudomonas dacunhae (ATCC

21192) was harvested and 26 g of this was mixed with 20 g of prepolymer A, followed by foaming as in Example 1, 3. The foam was cut into cubes of about 1 cm and packed into 3 a 100 cm column. As substrate was a 0.5 M L-aspartic acid solution, which additionally contained 2.5 g / l Tween 80 and 10 mg / l pyridoxal-5-phosphate and whose pH with H 2 SO 4 was 5.3 set, passed through the column. The flow rate was 0.65 ml / min, 35 giving a conversion to L-alanine of 14-17 mg / ml. The substrate was not recycled, so it passed through the column only once.

81 02 157 c * - Π -

After 700 ml of effluent was collected, the L-alanine was isolated therefrom by concentrating the solution at 85 ° C, adjusting the pH to 5.5 and then cooling to 15 ° C, causing a precipitate of L-aspartic acid and L- alanine crystallized.

This was taken up in deionized water, in which the L-alanine dissolved. After filtering out the L-aspartic acid, the filtrate was evaporated to dryness under vacuum to give 151.4 g of crude crystalline L-alanine.

Example V

After the column of Example IV had been in operation for about 2 weeks, the substrate was replaced with a solution containing 1 g mol L-aspartic acid and 125 ml ammonia per liter, the pH of which was adjusted to 5.3 by 60%. The flow rate was 0.65 ml / min. The conversion was now about 14 mg / ml. By replacing this substrate with another containing only 0.05 gmol L-aspartic acid per liter, the conversion dropped to 4-5 mg / ml.

Several experiments with 1 M substrate gave conversions from 27 to 32 mg / ml. When recirculating, 2X7 conversions of 45 to 50 mg / ml were achieved. By adding 12.5 mg / l pyridoxal-5-phosphate, the conversion increased to about 36 mg / ml. Subsequent experiments without pyridoxal-5-phosphate but with recirculation increased the conversion to 45 mg / ml. After the column had been in continuous use for about 45 days

However, the conversion rate has decreased to 16 mg / ml. However, most of the time he had worked without pyridoxal-5-phosphate, and when 12.5 mg / l of this had been added, the conversion rose again to about 40 mg / ml. Then, when the same solution was recycled through the column for 24 days, the pH rose

30 of that solution to 8.72 which meant a conversion of more than 90%. The L-alanine was now determined in the effluent (using the automatic procedure of Example II), and 94% of the L-aspartic acid was found to have been converted to L-alanine.

Example VI

A suspension of E. coli cells (ATCC

11303) in phosphate buffer of pH = 8.0 was heated to 5000 81 02 157 * in 30 minutes. .

* * - 12 - rpm centrifuged off. The cell mass was allowed to drain further in the refrigerator overnight, after which 11 g were obtained. This was mixed with 11 g of prepolymer A. Due to the water in the cell mass, the prepolymer reacted into a flexible hydrophilic polyurethane foam, which cured in about 15 minutes. The cells were encapsulated or bound to the polyurethane foam matrix.

Example VII

After cooling the foam of Example VI in the refrigerator, it was cut into cubes of about 6 mm for later use. For a substrate, 11.6 g of fumaric acid and 20.3 mg of MgC2 .02. O were dissolved in 25% ammonia (pH -8.5), and made up to 100 ml with deionized water. This solution was brought to 37 ° C and about 1.4 g (dry matter) of the foam was suspended in this solution. After 30 minutes, thin layer chromatography showed that significant amounts of L-aspartic acid had formed. Further analysis showed that 95% of the fumaric acid had been used for the conversion to L-aspartic acid.

Example VIII

In a water-jacketed tube, 75 ml of the particulate foam of Example 6 was packed into a column. The temperature was set at 37 ° C and substrate was passed through the column at different flow rates. The substrate consisted of a solution of 232 g of fumaric acid, 400 ml of strong ammonia, and 406 mg of MgC 2 O 2 O in 2 liters of deionized water, the pH of which was adjusted to 9.0. The liquid volume of the column (that part of the column not occupied by foam) was 31.25 ml.

About 3500 ml of substrate was added at a constant flow rate of 0.6 ml / min. passed through the column. Samples were taken regularly and analyzed for high fumaric acid by chromatography. The progress of the conversion of the fumaric acid to L-aspartic acid over time was monitored, and was found to be as follows: 8102 157 *> - 13 - after 5 hours, the conversion was 71% after 46 hours, the conversion was 69% after 150 hours the conversion was 61% after 218 hours the conversion was 61%.

Example IX

After the column of Example VIII had been in operation for 54 hours, the flow rate was adjusted to 0.28 ml / min. and a 288 ml sample was collected over the next 16 hours and 50 minutes. The L-aspartic acid was isolated from 250 ml of this, and it was found that the actual conversion of fumaric acid to L-aspartic acid (based on a direct analysis by gas chromatography) was approximately 85%.

Example X.

About 3500 ml of the effluent from the column of Example VIII (at a flow rate of 0.60 ml / min) was collected. This was concentrated at 90 ° C and the pH was adjusted to 2.8 by adding 20 ml of 60% H 2 SO 2 (the isoelectric point of L-aspartic acid). Then it was cooled to 15 ° C and then the crystallized L-aspartic acid filtered off, dried, washed with 95% ethanol at 30 ° C. Unreacted fumaric acid dissolved in the ethanol and was thus removed. The remaining L-aspartic acid was found to be 97% pure when analyzed; the yield was 89%.

Example XI

In accordance with Example VI, a foam was prepared and 1 g of this was placed in a flask together with 100 ml of substrate (126 mg / ml fumaric acid, pH = 9). After 15 minutes at 37 ° C, the liquid was decanted and fresh substrate was added.

This change was performed three times. In the first decanter, a 57% conversion to L-aspartic acid was found, and in the three following decanters about 35%. The difference between the first batch and the later is attributed to the washing of improperly bound cells.

Example XII

In accordance with Example VIII, an 8102 157 4 * - 14 ---

column but its temperature was now set at 50 ° C. The same substrate used in Example 8 was continuously recycled through this column. Starting from the reductions in the fumaric acid content, the conversion to L-aspartic acid was essentially completed after 120 hours. Decrease to 33% and 10% of the initial level was reached after 30 hours and 50 hours, respectively (the latter found by extrapolation). Example XIII

The cells were harvested from a culture of AHV resistant Brevibacterium thiogenitalis. Of this, 5 g was mixed with 5 g of prepolymer A containing 2 wt% Pluronic L-62. After a foam was produced therefrom in accordance with Example 1, it was cut into cubes of about 2 cm, and weighed amounts containing about 0.42 g of wet cells were combined with 25 ml of substrate solution, which -3 -3 1.64 x 10 M α-ketoisocaproic acid, 1.70 x 10 M L-glutamic-5 acid and 5 x 10 M pyridoxal-5-phosphate and whose pH was adjusted to 8-9 with 2 N ammonia used to be. After several times at room temperature with continuous stirring (magnetic stirrer), samples were taken and analyzed for leucine. Generally, the foam was in contact with the substrate for 8 hours per day and was stored overnight in 0.05 M potassium phosphate buffer at 4-10 ° C, and used for a total of 5 days. The leucine determination was performed by semi-quantitative thin layer chromatography and quantitative high pressure chromatography. The stability of the cell / foam combination at room temperature was at pH = 8.0 and 9.0 (pH = 7.0 was found to be deleterious to activity).

30 8102 157 * = - -15-

Stability at pH. = »9.0 of the g-keto acid / leucine conversion_

Days Hours mgmol leucine per gram wet _ (Sample Time) weighted to bound cells 5 1 4 27.22 5 27.22 6 40.83 2 4 31.76 6 45.36 10 7 45.36 3 3 27.22 4 45 , 36 5 49.91 4 4 45.36 15 (after 72 hours 6 72.13 store in buffer 19 258.61 fer at 4-10 ° C) 22 285.85

The captured cells maintained their full transaminase activity for 4 days at room temperature. The gradual increase in leucine formation is attributed to activation, i.e., that the captured cells gradually lyse, allowing substrate to get to the active sites more easily and the product to get out of it more easily. This apparent "activation" was even more pronounced at pH = 8.0. In the first two days, the cell-containing foam showed very little activity, but on the third day there was a lot more, as the following figures show:

Stability at pH = 8.0 of the q-keto acid / leucine conversion 30 Days Hours mgmol leucine per gram wet

Sample time weight of bound cells _ '_ (70-85% water) 1 4-6 not to be determined 2 4-6 not to be determined 35 3 4 186.01 5 245.02 6 249.50 4 4 163.32 (after 72 hours were 294.88 (in buffer 6 267.64 at 4-10 ° C).

8102 157

Claims (17)

1. A method of preparing an L-amino acid, wherein a solution of an appropriate substrate is contacted with appropriate recorded microorganisms, characterized in that the microbe cells are contained in a hydrophilic polyester-polyurethane foam in which at least 50 mol% of the alkylene oxide units is ethylene oxide. A method according to claim 1, characterized in that the substrate solution has a pH between 3 and 11. Process according to claim 1 or 2, characterized in that the reaction takes place at a temperature between 15 ° and 60 ° C. Method according to any one of claims 1 to 3, characterized in that the method is carried out continuously. A method according to any one of claims 1 to 3, characterized in that the method takes place in portions. 6. A hydrophilic polyether polyurethane foam in which at least 50 mol% of the alkylene oxide units is ethylene oxide, characterized in that this foam contains encapsulated cells of an L-amino acid-forming microorganism. Foam according to claim 6, characterized in that at least 90 mol% of the alkylene oxide units are ethylene oxide. 8. Foam according to claim 6 or 7, prepared by reacting a hydrophilic polyether-urethane prepolymer with an aqueous suspension of L-amino acid-forming microbe cells. 9. A foam according to any one of claims 6,7 or 8, characterized in that the prepolymer was formed by reacting a mixture of a polyoxyethylene glycol and a polyhydric low molecular weight alcohol with an excess of polyisocyanate, Foam according to any one of claims 6 to 9, characterized in that it is rigid. Foam according to any one of claims 6 to 9, characterized in that it is flexible. 8102157 ft - 17 - Foam according to any one of claims 6 to II, characterized in that the weight ratio of polyurethane / microorganisms (based on dry matter) therein is between 1:10 and 10: 1. A process for preparing a hydrophilic polyether-polyurethane foam in which a culture of an L-amino acid-forming microorganism is mixed with a hydrophilic polyether-urethane prepolymer in which at least 50 mol% of the alkylene oxide units are ethylene oxide, and wherein there is enough water in the mixture to foam the prepolymer to encapsulate the microbe cells in the resulting foam. Method according to claim 13, characterized in that the water content of the microbe cells is between 10 and 90% by weight. A method according to claim 13 or 14, characterized in that the pH of the mixture is above 7. 16. Method according to any one of claims 13, 14 or 15, characterized in that the weight ratio of polymer / microbial cells (based on dry matter) is between 1:10 and 10: 1. 17. Method mainly according to description and / or examples. 25 8102157