JP2017136002A - Halobacteria capable of solidifying radionuclides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide microorganisms that can highly remove dissolved strontium (Sr) in a short time under conditions of high salt concentration and coexistence of cobalt (Co).SOLUTION: Provided is a microorganism that produces a urease, and can solidify and remove 90% or more of a dissolved radionuclide (1 mM) under a condition of 0.3-5% NaCl concentration within two days from the start of culture.SELECTED DRAWING: None

Description

  The present invention relates to halophilic bacteria having the ability to solidify radionuclides. The present invention further relates to a method for recovering radionuclides by the halophilic bacteria.

  Calcium carbonate (calcite) and calcium phosphate (apatite) produced by microorganisms are called biominerals (biocalcite, bioapatite). Research on purification by coprecipitation and adsorption of radioactive Sr in groundwater and soil using biominerals is being promoted (Non-Patent Documents 1 to 4). On the other hand, studies on purification of radioactive Sr by microbial metabolites under high salt concentration conditions such as seawater (3% salt concentration) have not been conducted.

Biocalcite, a kind of biomineral, is produced by the combination of carbonate ions formed by hydrolysis of urea by urease produced by microorganisms and Ca ions in solution (Reaction Formulas 1 and 2). (Non-Patent Documents 1 and 5). When calcite is generated, dissolved Sr ions are combined with carbonate ions, co-precipitated with calcite as strontium carbonate, and removed from the solution (Reaction Formula 2).
H ₂ NCONH ₂ + 3H ₂ O → 2NH ₄ ⁺ + HCO ₃ ⁻ + OH ⁻ (Scheme 1)
Sr ²⁺ / Ca ²⁺ + 2HCO ₃ ⁻ → Sr / CaCO ₃ + CO ₂ + H ₂ O (reaction formula 2)

  The present inventor has reported the TK2d strain as a microorganism belonging to the genus Bacillus that produces urease and has the ability to solidify a radionuclide under the condition of a NaCl concentration of 3% (Coprecipitation of radioactive strontium in sea water during formation of biogeneic calcite.T. Ohnuki, N. Kozai, F. Sakamoto, T. Saito, Q. Yu, M. Yamashita, T. Horiike, S. Utsunomiya. 15th International Conference on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere. September 13-18, 2015, Santa Fe Community Convention Center, Santa Fe, NM, USA). The TK2d strain is described in Japanese Patent Application No. 2015-133419.

Y. Fujita, et al., "Stimulation of microbial urea hydrolysis in groundwater to enhance calcite precipitation," Environ. Sci. Technol., Vol. 42, no. 8, pp. 3025-3032, 2008 Y. Fujita, et al., "Evaluating the potential of native ureolytic microbes to remediate a 90Sr contaminated environment," Environ. Sci. Technol., Vol. 44, no. 19, pp. 7652-7658, 2010 V. Achal, et al., "Bioremediation of strontium (Sr) contaminated aquifer quartz sand based on carbonate precipitation induced by Sr resistant Halomonas sp.," Chemosphere, vol. 89, no. 6, pp. 764-768, 2012 S. Handley-Sidhu, et al., "Bacterially Produced Calcium Phosphate Nanobiominerals: Sorption Capacity, Site Preferences, and Stability of Captured Radionuclides," 2014 Y. Fujita, et al., "Strontium incorporation into calcite generated by bacterial ureolysis," Geochim. Cosmochim. Acta, vol. 68, no. 15, pp. 3261-3270, 2004

  The problem to be solved by the present invention is to provide a microorganism capable of highly removing dissolved strontium (Sr) in a short time under a high salt concentration condition and in the presence of cobalt (Co), and a radionuclide using the microorganism. It is to provide a way to solidify.

  In order to solve the above-mentioned problems, the present inventor has separated urease producing microorganisms under high salt concentration conditions and examined whether or not Sr solidified product is produced as strontium carbonate. In addition, it was found that dissolved strontium (Sr) can be highly removed in a short time in the presence of cobalt (Co), and the present invention has been completed.

That is, the aspect of the present invention relates to the following.
[1] A microorganism that produces urease and has the ability to solidify and remove 90% or more of 1 mM dissolved radionuclide within 2 days from the start of culture under the conditions of NaCl concentration of 0.3% to 5%.
[2] A microorganism that produces urease and has the ability to solidify a radionuclide under the conditions of NaCl concentration of 0.3% to 5% and in the presence of cobalt (Co).
[3] Produces urease and has the ability to solidify and remove 90% or more of 1 mM dissolved radionuclide within 2 days from the start of culture under the conditions of NaCl concentration of 0.3% to 5%, and further, the NaCl concentration is 0 A microorganism having the ability to solidify a radionuclide under conditions of 3% to 5% and in the presence of cobalt (Co).
[4] Any one of [1] to [3], having an ability to solidify and remove 95% or more of a 1 mM dissolved radionuclide within a day from the start of culture under a condition where the NaCl concentration is 0.3% to 3%. The microorganism described in 1.
[5] Under the condition of NaCl concentration of 0.3% to 3%, on the first day after the start of the culture, it grows to the number of cells at least 1 × 10 ⁶ times the number of the cells at the start of the culture. The microorganism according to any one of [1] to [4], wherein the number of cells at 1 × 10 ⁶ times or more of the number of cells at the start of culture is maintained until the third day.
[6] The microorganism according to any one of [1] to [5], wherein the radionuclide is strontium (Sr).
[7] The microorganism according to [6], which has an ability to solidify strontium (Sr) as a complex carbonate of strontium (Sr) and calcium (Ca).
[8] The microorganism according to any one of [1] to [7], which belongs to the genus Sporosarcina.
[9] A microorganism having a deposit number of NITE BP-02190.

[10] A method for solidifying a radionuclide, comprising culturing the microorganism according to any one of [1] to [9] in a liquid containing a radionuclide.
[11] The method according to [10], wherein the liquid containing the radionuclide has an NaCl concentration of 3% or more.
[12] The method according to [10] or [11], wherein the liquid containing a radionuclide is a liquid containing calcium ions.
[13] The method according to any one of [10] to [12], wherein the liquid containing the radionuclide is a liquid containing cobalt (Co).
[14] The method according to any one of [10] to [13], wherein the radionuclide is strontium (Sr).
[15] A method for recovering a radionuclide comprising a step of solidifying a radionuclide in a liquid containing a radionuclide and a step of recovering the solidified radionuclide by the method according to any one of [10] to [14] .

  The microorganism of the present invention is a novel microorganism having an ability to recover a radionuclide. By using the microorganism of the present invention, radionuclides can be recovered in a short time under high salt concentration conditions and in the presence of cobalt (Co).

FIG. 1 shows the red halo of the degradation plate medium. FIG. 2 shows the result of the dissolved Sr removal ability test of the candidate strain. FIG. 3 shows a phylogenetic tree based on 16S rRNA gene analysis of KW3b1 and KW3b2 strains. FIG. 4 shows a comparison of the Sr removal ability of the TK2d strain, the KW3b1 strain, and the KW3b2 strain. FIG. 5 shows the result of the Sr removal ability test of KW3b1 strain to examine the influence of NaCl. FIG. 6 shows the results of a cell growth test of KW3b1 strain to examine the influence of NaCl. FIG. 7 shows the results of the Co resistance test of the TK2d strain, KW3b1 strain, and KW3b2 strain. FIG. 8 shows the results of observation of solidified Sr synthesized by the TK2d strain, KW3b1 strain, and KW3b2 strain. FIG. 9 shows the results of observation of solidified Sr synthesized by the KW3b1 strain. FIG. 10 shows the results of observation of solidified Sr synthesized by the KW3b1 and KW3b2 strains.

Embodiments of the present invention will be described below.
The microorganism of the present invention is a microorganism that produces urease and has the ability described in (1) and / or (2) below.
(1) Ability to solidify and remove 90% or more of 1 mM dissolved radionuclide (for example, strontium etc.) within 2 days from the start of culture under the condition of NaCl concentration of 0.3% to 5%;
(2) Ability to solidify radionuclides (for example, strontium, etc.) under a NaCl concentration of 0.3% to 5% and in the presence of cobalt (Co):

  The ability of microorganisms to produce urease can be determined by using the increase in pH of the medium due to hydrolysis of urea as an indicator of the urease activity of microorganisms. For example, the pH increase of the medium can be visualized by utilizing the color reaction of Phenol red that changes from yellow to red at pH 8 or higher. Since the urease-producing microorganism forms a red halo around the colony, the ability of the microorganism to produce urease can be determined by observing the red halo.

  The microorganism of the present invention is characterized by having the ability to solidify the radionuclide under the condition of NaCl concentration of 0.3% to 5%. Other salt may be contained as the condition of the NaCl concentration of 0.3% to 5%, and seawater is an example that satisfies the condition of the NaCl concentration of 3%.

  The microorganism of the present invention is preferably 95% or more, more preferably 98% or more, more preferably 99% of 1 mM dissolved radionuclide (for example, strontium) under the condition of NaCl concentration of 0.3% to 3%. It has the ability to solidify and remove the above within one day from the start of culture.

The microorganism of the present invention preferably has a cell number of 1 × 10 ⁶ times or more of the number of cells at the start of the culture on the first day after the start of the culture under the condition of NaCl concentration of 0.3% to 3%. Proliferate and maintain the number of cells at least 1 × 10 ⁶ times the number of cells at the start of culture until 3 days after the start of culture.

  The radionuclide means a radionuclide that is sometimes called a radioisotope. Radionuclides include natural radionuclides existing in nature (uranium 238, potassium 40 and radium 226, thorium 232, etc.) and artificial radionuclides (cesium 134, cesium 137, iodine 131, xenon 133, strontium 89, strontium 90, krypton. 85, zirconium 95, ruthenium 106, cerium 144, cobalt 60, carbon 14, thorium 232) and the like.

  The microorganism of the present invention only needs to have the ability to solidify at least one of the radionuclides described above. Preferably, the microorganism of the present invention is a microorganism having an ability to solidify an artificial radionuclide, more preferably a microorganism having an ability to solidify strontium (Sr).

  The microorganism of the present invention is preferably a microorganism capable of solidifying a radionuclide as a carbonate, and particularly when calcium ions are present, the radionuclide is solidified as a composite carbonate of a radionuclide and calcium (Ca). Is a microorganism that can. As an example of the microorganism of the present invention, a microorganism having the ability to solidify strontium (Sr) as a complex carbonate of strontium (Sr) and calcium (Ca) can be mentioned.

  In the present invention, solidification means that the radionuclide dissolved in the liquid is insolubilized. The ability of the microorganism to solidify the radionuclide can be confirmed by the method described in the Examples. Specifically, after inoculating a microorganism-containing medium to which a liquid containing a radionuclide is added with a sample containing the microorganism and culturing the microorganism under conditions that allow the microorganism to grow, the radionuclide in the supernatant of the sampling sample is measured. The ability to solidify the radionuclide can be measured. The microorganism of the present invention can be isolated and collected by screening from wild strains, mutant strains and the like by the method described above or a method similar thereto.

  The genus to which the microorganism of the present invention belongs is not particularly limited. A method of classifying microorganisms (identification of genus species) based on 16S rRNA information and the like for microorganisms collected from environmental samples and the like is known. The microorganism used in the present invention may be any microorganism such as a wild-type strain, a mutant strain, and a recombinant produced by genetic engineering techniques.

  The genus to which the microorganism of the present invention belongs is preferably a microorganism belonging to the genus Sporosarcina. In the present invention, a microorganism having a homology of 95% or more, preferably 98% or more, more preferably 99% or more with a microorganism belonging to Sporosarcina in the base sequence of 16S rRNA gene can be used.

  As an example of the microorganism belonging to the genus Sporosarcina, the KW3b2 strain isolated in the examples of the present specification can be mentioned. The KW3b2 strain was registered under the accession number NITE BP-02190 on January 12, 2016, at the National Institute of Technology and Evaluation of Microorganisms (Postal Code 292-0818, 2-5 Kazusa Kamashichi, Kisarazu City, Chiba Prefecture, Japan). 8). The KW3b2 strain has a microbiological characteristic that colonies are pale yellow, round and smooth, and catalase and oxidase are positive in LB medium, gonococci (0.7-0.8x1.5-2.5 μm) ing. The 16S rRNA gene sequence of the KW3b2 strain is shown in SEQ ID NO: 5.

  As a medium used for culturing the KW3b2 strain, LB medium (Trypron 10 g / L, Yeast Extract 5 g / L, NaCl 5 g / L, NaCl 30 g / L) is preferable, but it can also be grown in Marine Broth 2216. The pH of the medium (before sterilization) is preferably 7.6. The culture temperature is preferably 30 ° C., and the culture period is preferably 1 to 2 days. The culture is aerobic culture, preferably shaking culture.

Furthermore, according to this invention, the method of solidifying a radionuclide including culturing the microorganism of this invention mentioned above in the liquid containing a radionuclide is provided.
The liquid containing the radionuclide is preferably a NaCl concentration of 3% or more, more preferably a liquid containing calcium ions, and a liquid containing cobalt (Co) is also preferable. Seawater can be given as a liquid that satisfies the above conditions. Specific examples of the radionuclide to be solidified are as described above, and particularly preferably strontium (Sr).

  The method for culturing the microorganism of the present invention is not particularly limited as long as the radionuclide can be solidified, and suitable culture conditions can be appropriately selected according to the properties of the microorganism to be used. For example, in the case of the KW3b2 strain used in the examples, the culture is performed at a temperature of 25 to 40 ° C., preferably at a temperature of 25 to 35 ° C., particularly preferably at 28 to 32 ° C. under aerobic conditions such as shaking culture. Can do.

  According to the present invention, after solidifying the radionuclide in the liquid containing the radionuclide by the above-described method, the solidified radionuclide can be recovered. The collection of the radionuclide can be performed by a known method such as centrifugation, filter filtration, or a combination thereof.

  The method for solidifying a radionuclide according to the present invention can be applied to a liquid containing a radionuclide (for example, seawater contaminated with a radionuclide).

  The present invention will be described more specifically with reference to the following examples, but the present invention is not particularly limited by the following examples.

(1) Test method (1-1) Marine environmental sample As the source of microorganisms, seabed mud from Kagoshima Bay (4 locations) was collected. Environmental samples were diluted to 10% (w / v) with sterile saline (NaCl 0.9% (w / v)) and mixed by vortexing. These environmental sample dilutions were used for screening.

(1-2) Medium Medium (pH 7.6) in which NaCl (30 g / L) and urea (20 g / L) were added to Marine Broth 2216 (MB; 3.74 g / L) (Becton Dickinson and Company, MD, USA). ) Was used as the basal medium. As a separation medium, pH indicator Phenol red (12 mg / L) was added to MB. As a medium for Sr removal test, SrCl ₂ solution was added to MB so that the final concentration of Sr was 1.0 mM. In the screening, stationary culture was performed, and in the Sr removal test, shaking culture at 120 rpm was performed at a temperature of 30 ° C. In order to characterize the Sr solidification ability, MB (filtered MB) was used in which insoluble components generated in the medium after autoclaving were removed by filtration with a filter (0.45 μm pore size, Corning, NY, USA). Agar (15 g / L) was used when preparing solid media.

(1-3) Search for urease-producing microorganisms In order to remove radionuclides in seawater with biocalcite, separation of microorganisms producing urease in the presence of high salt concentration from marine environmental samples was attempted. The increase in pH of the medium due to hydrolysis of urea (Reaction Formula 1) was used as an indicator of urease activity of microorganisms. That is, the pH increase of the plate medium for separation was visualized using the color reaction of Phenol red that changes from yellow to red at pH 8 or higher. It seems that urease-producing microorganisms form a red halo around the colonies in the separation plate medium. By observing this red halo, the presence or absence of urease activity of the microorganism is determined. The diluted environmental sample solution (20 μL) was smeared on a separation plate medium and statically cultured at 30 ° C. until colonies appeared. Of the colonies that appeared, only the strains that formed red halos were subcultured to a new separation plate medium. A strain in which reproducibility of a red halo was obtained after repeating subculture twice was designated as a urease production candidate strain. These candidate strains were subjected to the Sr removal test described below.

(1-4) Sr removal test by candidate strain In order to clarify the generation of calcite containing Sr at the time of removal of dissolved Sr of the candidate strain, the change with time of the Sr concentration in the culture liquid was examined. Candidate strains were aseptically inoculated into a glass test tube containing 10 ml of MB using a platinum loop and pre-cultured (30 ° C., 120 rpm) for 12 hours. The preculture was inoculated with 1% (v / v) in a 50 ml test medium in a 125 ml Erlenmeyer flask and main cultured (30 ° C., 120 rpm, Sr 1.0 mM) for 7 days. Sampling was done in a timely manner. The sampled culture broth was centrifuged (2,1000 × g, 15 min, 4 ° C.) and fractionated into a supernatant and a precipitate. The obtained supernatant was filtered with a filter (0.2 μm pore size, KURABO, Osaka, Japan) and used as a sample for analysis of element concentration. The precipitate was used as a sample for cell observation and solid analysis. MB not inoculated with the candidate strain was used as a control under the same conditions.

In the Sr removal test for examining the influence of NaCl, the NaCl concentration was set to 0.3%, 3%, 5%, and 10%.
In the Co resistance test, the experiment was performed under the following conditions.
Culture medium:
Marine broth; 3.7 g / L (containing 0.3% NaCl),
Urea; 20 g / L
NaCl addition; 30 g / L
Co concentration: final concentration 0.06 mM
Sr concentration: final concentration 0.01 mM (derived from medium)
Inoculum: 1% (v / v) inoculum culture conditions:
50mL in 100mL Erlenmeyer flash
30 ° C., 120 rpm, pH 7.6

(1-5) Characterization of Sr solidification ability by isolates In order to clarify the influence on the Sr solidification ability due to the difference in the initial dissolved Sr concentration, a Sr removal test was performed using the filtered MB. The test was performed for 10 days in the same manner as the Sr removal test described above, with the initial dissolved Sr concentration set to 5.0 mM, 1.0 mM, 0.1 mM, and 0.02 mM. Sampling was performed in a timely manner, and an analysis sample was prepared by the same method as described above. The filtered supernatant was used as an analysis sample for element concentration. The precipitate was used as a sample for cell observation and solid analysis. Filtered MB not inoculated with the isolate was used as a control under the same conditions.

(1-6) element concentration analyzing undiluted ultrapure water each analytical sample ^{(Barnstead NANOpure R DIamond, Thermo Fisher} Scientific, Rockford, IL, USA) diluted appropriately, inductively coupled plasma emission spectrometer (ICP-AES Elemental quantification was carried out by iCAP6300DUO: Thermo Fisher Scientific). A calibration curve was prepared using a standard solution for calibration curve (XSTC-622: SPEX CetriPrep, NJ, USA). Measurement was repeated three times per sample, and the average value of deviations within 5% was taken as the measurement result.

(1-7) Bacterial cell observation with a scanning electron microscope and elemental analysis with an energy dispersive X-ray analyzer The precipitate obtained from the culture solution is washed three times with 0.9% sterilized physiological saline and then sterilized. It was used for observation after being washed once with ion-exchanged water. The sample was dropped on an observation filter (Nano-Percolorator, JEOL, Tokyo, Japan) and then sucked with a syringe to obtain an electron microscope observation sample. A desktop electron microscope (SEM; TM3000: Hitachi High-Technologies, Tokyo, Japan) is used for observation, and an energy dispersive X-ray analyzer (EDX; Quantax70: Bruker AXS Microanalysis, Karlsrh is used for elemental analysis). It was.

(1-8) Molecular biology test (determination of the base sequence of 16S rRNA gene)
In order to identify the genus species of the isolate, the base sequence of the 16S rRNA gene was determined. Isolates cultured for 3 days in MB were collected by centrifugation (21,000 × g, 4 ° C., 5 minutes), washed twice with 0.9% sterile saline, and then genomic. DNA was extracted according to the protocol of ISOPLANT (Nippon Gene, Tokyo, Japan). PCR amplification of 16S rRNA gene was performed using 9F (5'-GAGTTTGATCCTGGCTCAG-3 ') (SEQ ID NO: 1) and 1541R (5'-AAGGAGGTGATCCAGCC-3') (SEQ ID NO: 2) primer set using the extracted genomic DNA as a template. , Using GO Taq Green Master Mix (Promega, Tokyo, Japan) at 95 ° C. for 5 minutes, followed by the following conditions (denaturation (95 ° C., 1 minute), annealing (56 ° C., 1 minute), extension (72 ° C., 1 minute) Min)) for 30 cycles. This reaction was carried out using a PCR amplifying device Mastercycler (Eppendorf, Tokyo, Japan). The amplified DNA was purified using the ^{Wizard R SV gel and PCR Clean-} Up System (Promega). The 16S rRNA gene base sequence was prepared using a plurality of primers (9F, 515F (5′-GTGCCAGCAGCCGCGGT-3 ′) (SEQ ID NO: 3), 1115R (5′-AGGGTTGCGCTCGTTG-3 ′) (SEQ ID NO: 4) using purified DNA as a template. 1541R) was determined and analyzed by Applied Biosystems 3730xl DNA Analyzer (Applied Biosystems, CA, USA).

(1-9) Creation of Phylogenetic Tree The determined 16S rRNA gene sequence was obtained from BLAST (SF Altschul, et al., “Basic local alignment search tool,” J. Mol. Biol., Vol. 215, no. 3, pp provided by NCBI. (403-410, 1990) (http://blast.ncbi.nlm.nih.gov/Bla-st.cgi). Based on the base sequence of the bacterial species that showed high homology, neighbor-joining method (N. Saitou, et al., "The neighbor-joining" using CLASTAL W and phylogenetic tree generation software Molecular Evolutionary Genetics Analysis (MEG5.0) A new method for reconstructing phylogenetic trees, "Mol. Biol. Evol., vol. 4, no. 4, pp. 406-425, 1987).

(2) Results and discussion (2-1) Isolation of halophilic calcite-producing microorganisms As a result of attempts to isolate urease-producing microorganisms from seabed mud samples, red halos (Fig. 1) were formed on the separation plate medium. Colonies were obtained. Since these colonies were subcultured and repeatedly formed red halos, they were considered as candidate strains that stably produce urease.

  In order to investigate whether these microorganism candidate strains produce Sr solidified product, the concentration of dissolved Sr in the culture liquid of the eight candidate strains was measured over time. It was found that the concentration of dissolved Sr in each culture liquid on the second day of culture decreased from the initial concentration of 1.0 mM to 0.02 mM in the KW3b strain, and the KW3b strain removed 98% of the dissolved Sr in the second day of culture. did. Hereinafter, an experiment was performed on the KW3b strain having the largest decrease in dissolved Sr. Since the KW3b strain was found to contain two types of strains having different colony colors, the KW3b1 strain and the KW3b2 strain were isolated by colony isolation.

(2-2) Phylogenetic identification of KW3b1 and KW3b2 strains In order to molecularly identify KW3b1 and KW3b2 strains, a partial base sequence of 16S rRNA gene was decoded and homology search was performed. . Among the 16S rRNA genes of the KW3b1 and KW3b2 strains, a partial sequence of 1431 bases (SEQ ID NO: 5 in the sequence listing) was clarified. The nucleotide sequences of the KW3b1 and KW3b2 strains were 100% identical.
When this nucleotide sequence was compared with the BLAST database, it was found that Sporosarcina soli was 99.3%, Sporosarcina contaminans was 99.0%, and Sporosarcina ginsengisoli was 99.0% homologous. The phylogenetic tree based on the 16S rRNA gene of these microorganisms showed that the KW3b1 and KW3b2 strains were classified into the genus Sporosarcina (FIG. 3).

(2-3) Sr removal ability of KW3b1 strain and KW3b2 strain Sr removal ability of KW3b1 strain and KW3b2 strain was tested (FIG. 4). In the KW3b1 and KW3b2 strains, the dissolved Sr was reduced from the initial concentration of 1 mM to 0.01 mM or less on the first day of culture. Assuming that the initial concentration of Sr is 100%, KW3b1 strain and KW3b2 strain removed dissolved Sr 99% or more in one day. The KW3b1 and KW3b2 strains had higher Sr removal ability than the comparative TK2d strain.

(2-4) Sr removal ability test and cell growth test of KW3b1 strain The NaCl concentration was set to 0.3%, 3%, 5% and 10% to evaluate the Sr removal ability and cell growth of KW3b1 strain. did. The results are shown in FIGS.
The optimum NaCl concentration for Sr removal rate of KW3b1 strain was 0.3% and 3%, and the optimum NaCl concentration for growth was 3.0%. The KW3b2 strain had the same results as the KW3b1 strain.

(2-5) Co resistance test of KW3b1 and KW3b2 strains The results of evaluating the Sr removal ability in the presence of Co in the KW3b1 and KW3b2 strains are shown in FIG.
Kr3b1 and KW3b2 strains were able to remove Sr under Co dissolution.
The TK2d strain did not grow at Co 0.06 mM (3.5 mg / L).

  The results from the above (2-3) to (2-5) are summarized in Table 1 below. The KW3b1 strain and the KW3b2 strain show excellent Sr removal ability (Sr removal rate, NaCl resistance, Co resistance).

(2-6) Observation of solidified Sr synthesized by KW3b1 strain and KW3b2 strain The solidified product produced by KW3b1 strain and KW3b2 strain on the fifth day of culture was analyzed by SEM-EDX (FIGS. 8 to 10).
FIG. 8 compares the shapes of precipitates (solidified Sr) synthesized by the TK2d strain, the KW3b1 strain, and the KW3b2 strain. The three-dimensional structure of the precipitate was different depending on the strain, and the KW3b1 and KW3b2 strains were coronal.

FIG. 9 shows the SEM image of the solidified Sr synthesized by the KW3b1 strain and the results of EDX analysis. The KW3b1 strain was shown to synthesize approximately 10 μm coronal Sr / Ca solidified material.
FIG. 10 shows the observation results of solidified Sr synthesized by the KW3b1 and KW3b2 strains. KW3b1 and KW3b2 strains were shown to synthesize the same coronal Sr solidified product.

(3) Summary The results obtained by this example are as follows.
A strain showing a decrease in dissolved Sr was isolated from the Kagoshima Bay submarine mud sample. Among these, the KW3b1 and KW3b2 strains can be used at a salt concentration of 0.3 to 5%, have high Sr removal ability, and can be used even in the presence of Co. The KW3b1 strain and the KW3b2 strain are particularly suitable when it is desired to remove Sr quickly and when it is desired to remove Sr in the Co-containing solution.

Claims (15)

A microorganism producing urease and capable of solidifying and removing 90% or more of 1 mM dissolved radionuclide within 2 days from the start of culture under the condition of NaCl concentration of 0.3% to 5%. A microorganism that produces urease and has the ability to solidify radionuclides under the conditions of NaCl concentration of 0.3% to 5% and in the presence of cobalt (Co). It produces urease and has the ability to solidify and remove 90% or more of 1 mM dissolved radionuclide within 2 days from the start of culture under the conditions of NaCl concentration of 0.3% to 5%, and further, the NaCl concentration of 0.3% Microorganisms having the ability to solidify radionuclides under ~ 5% conditions and in the presence of cobalt (Co). 4. The method according to any one of claims 1 to 3, which has an ability to solidify and remove 95% or more of 1 mM dissolved radionuclide within a day from the start of culture under a condition of NaCl concentration of 0.3% to 3%. Microorganisms. Under the condition of NaCl concentration of 0.3% to 3%, on the first day after the start of the culture, the cells grew to the number of cells that is 1 × 10 ⁶ times or more the number of the cells at the start of the culture, and the third day after the start of the culture. The microorganism according to any one of claims 1 to 4, wherein the number of cells at least 1 x 10 ⁶ times the number of cells at the start of culture is maintained. The microorganism according to any one of claims 1 to 5, wherein the radionuclide is strontium (Sr). The microorganism according to claim 6, which has an ability to solidify strontium (Sr) as a complex carbonate of strontium (Sr) and calcium (Ca). The microorganism according to any one of claims 1 to 7, which belongs to the genus Sporosarcina. A microorganism having an accession number of NITE BP-02190. A method for solidifying a radionuclide, comprising culturing the microorganism according to any one of claims 1 to 9 in a liquid containing the radionuclide. The method according to claim 10, wherein the liquid containing the radionuclide has an NaCl concentration of 3% or more. The method according to claim 10 or 11, wherein the liquid containing a radionuclide is a liquid containing calcium ions. The method according to any one of claims 10 to 12, wherein the liquid containing a radionuclide is a liquid containing cobalt (Co). The method according to any one of claims 10 to 13, wherein the radionuclide is strontium (Sr). A method for recovering a radionuclide comprising the steps of solidifying a radionuclide in a liquid containing a radionuclide and recovering the solidified radionuclide by the method according to any one of claims 10 to 14.