A process for producing riboflavin

Abstract: A process for producing riboflavin efficiently at a low cost comprises culturing in a medium a microorganism carrying a recombinant DNA prepared by inserting into a DNA vector a DNA which is derived from a microorganism belonging to the genus Corynebacterium or Brevibacterium and which, upon introduction into a riboflavin-requiring microorganism, confers on the microorganism the ability to complement its riboflavin requirement. Riboflavin accumulates in the culture and can be recovered.

Description: The present invention relates to a process for producing riboflavin (vitamin B2). Riboflavin is an important vitamin which is useful in medicaments, feed additives, coloring agents for food, etc. Processes for producing riboflavin by fermentation, processes characterized by culturing mutant strains of Eremothecium ashbyii , Ashbya gossypii , Candida flareri , Saccharomyces cerevisiae , etc. are known (Progress Industrial Microbiology, 1 , 139 (1959), U.S. Patent No. 5,164,303 and Japanese Published Unexamined Patent Application No. 112,996/88. Patent Abstracts of Japan Vol. 14 no. 377 August 15 1990 No. 2-138-988 discloses the production of flavin mononucleotide and flavin adenine dincleotide from a precursor thereof by reaction of the precursor with adenosine 5' triphosphate in the presence of a microorganism of the genus Corynebacterium or Brevibacterium holding a recombinant DNA coding for the enzymes involved with the biosynthesis of flavin mononucleotide or flavin adenine dinucleotide. In addition, European Publication No. 405,370 describes that genetically engineered microorganisms belonging to the genus Bacillus in which Bacillus -derived genes encoding enzymes involved in the biosynthesis of riboflavin are introduced, are used for riboflavin production. The publication contains a description of Bacillus -derived genes encoding enzymes involved in the biosynthesis of riboflavin, but there is no specific description of a DNA which is derived from a microorganism belonging to the genus Corynebacterium or Brevibacterium and which, upon introduction into a riboflavin-requiring microorganism, confers on the microorganism the ability to complement its riboflavin requirement. The object of the present invention is to provide a process for producing riboflavin efficiently at a lower cost. Thus the present invention is directed to a DNA which is derived from a microorganism belonging to the genus Corynebacterium and which, upon introduction into a riboflavin-requiring microorganism, confers on the microorganism the ability to complement its riboflavin requirement. In accordance with one aspect of the invention, there is provided an isolated DNA which is derivable from a microorganism belonging to the genus Corynebacterium and which, upon introduction into a riboflavin-requiring host microorganism is capable of conferring on the microorganism the ability to complement its riboflavin requirement, the DNA encoding at least guanosine triphosphate cyclohydrolase and riboflavin synthase. The invention also provides a recombinant DNA comprising said DNA and a vector DNA; a microorganism carrying said recombinant DNA, and a process for producing riboflavin by culturing said microorganism in a medium until riboflavin has accumulated in the culture, and recovering the riboflavin therefrom. In the accompanying drawings: FIG. 1 shows restriction enzyme maps for plasmids pFM21 and pFM41. FIG. 2 shows a restriction enzyme map for plasmid pFM201. As the DNA of the present invention, any DNA is appropriate so long as it is derived from a microorganism belonging to the genus Corynebacterium and which, upon introduction into a riboflavin-requiring microorganism, confers on the microorganism the ability to complement, its riboflavin requirement. The DNA is presumed to bear genetic information on enzymes involved in the biosynthesis of riboflavin, because the DNA, upon introduction into a riboflavin-requiring microorganism lacking the enzyme activity involved in the biosynthesis of riboflavin, confers on the microorganism the ability to grow in a riboflavin-free medium. Specially, the DNA of the present invention is a DNA having the nucleotide sequence set forth in SEQ. ID No. 1. Moreover, DNAs having a partial sequence thereof or having a partially replaced sequence by another nucleotide sequence, can be used as the DNA of the present invention as long as it confers on a riboflavin-requiring microorganism the ability to complement its riboflavin requirement. For example, a 2.7 kb DNA fragment having the nucleotide sequence from position 1476 to position 4164 in SEQ. ID No. 1 is mentioned. The DNA fragment contains the genes encoding at least two enzymes involved in the biosynthesis of riboflavin, guanosine triphosphate cyclohydrolase and riboflavin synthase. As the donor source of the DNA of the present invention, a microorganism belonging to the genus Corynebacterium preferably Corynebacterium ammoniagenes , is mentioned. Paticularly, Corynebacterium ammoniagenes KY13313 (Amino acid Nucleic acid, 22, 15 (1970)) is the most preferred. A chromosomal DNA (a donnor DNA) is obtained from the donor microorganism in a conventional manner, for example by extraction of a chromosomal DNA with phenol [Biochem. Biophys. Acta., 72, 619 (1963)]. As a vector DNA into which the DNA of the present invention is inserted, any of the phage vectors, plasmid vectors, etc., is suitable so long as it is autonomously replicable in a microorganism belonging to the genus Corynebacterium, Brevibacterium or Escherichia. Preferable examples are pCG1, pCG2, pCG4, pCG11, pCE52, pCE53 and pCE54 (U.S. Patent Nos. 4,617,267, 4,500,640 and 4,710,471). A recombinant DNA comprising a vector DNA and the DNA which is derived from a microorganism belonging to the genus Corynebacterium and which, upon introduction into a riboflavin-requiring microorganism, confers on the microorganism the ability to complement its riboflavin requirement, can be obtained together with a variety of recombinant DNAs by cleaving a donor DNA and a vector DNA with suitable restriction enzymes e.g. Pst I and Bgl II and then ligating both DNAs by the action of DNA ligase. The mixture of ligated DNAs thus obtained is used for transform a recipient. Any of the riboflavin-requiring microorganism belonging to the genus Corynebacterium or Brevibacterium and lacking the enzyme activity involved in the biosynthesis of riboflavin can be used as the recipient. For example, Corynebacterium ammoniagenes RK122 (Example 4) can be used as the recipient. The recipient is transfarmed with the variety of recombinant DNAs thus obtained in a conventional method, such as the protoplast method (Japanese Published Unexamined Patent Application No. 248,394/88), the electroporation method [W. J. Dower et al., Nucleic Acids Research, 16, 6127 (1988)] and the method of Cohen et al. [Proc. Natl. Acad. Sci., USA, 69, 2110 (1979)]. A transformant having the desired enzyme activity involved in the biosynthesis of riboflavin, can be obtained by selecting a transformant capable of growing in a riboflavin-free medium from the transformants thus obtained. If the vector DNA contains a selective marker e.g. a resistance to an antibiotic, the desired transformant can be more easily be selected by addition of the antibiotic to the selective medium. The desired recombinant DNA can be isolated from the thus selected transformant and then introduced into another microorganism belonging to the genus Corynebacterium or Brevibacterium in a conventional method. Alternatively, the inserted DNA may be excised from the recombinant DNA and ligated to another vector DNA, and then the DNA can be introduced into a microorganism belonging to the genus Corynebacterium or Brevibacterium . Such microorganism includes, for example, Corynebacterium ammoniagenes , KY13313, etc. Using other bacterial host-vector system, the DNA of the present invention can also be introduced into another bacterial species. Any of known host-vector systems such as those of the genus Escherichia , Bacillus , etc. can be used. Specifically, Escherichia coli JM105 [GENE, 33 , 103 (1985)] is mentioned for this purpose. As the transformant having the desired enzyme activity, mention may be made of Corynebacterium ammoniagenes KY13313/pFM21 and KY13313/pFM41. KY13313/pFM21 and KY13313/pFM41 carry the recombinant DNAs pFM41, respectively. pFM21 and pFM41 contain the DNA of the present invention. Corynebacterium ammoniagenes KY13313/pFM41 has been deposited as Corynebacterium ammoniagenes FM41 (FERM BP-4003) with the National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology, Japan, as from September 9, 1992, under the Budapest Treaty. Riboflavin can efficiently be produced at a lower cost by culturing a microorganism belonging to the genus Corynebacterium , Brevibacterium or Escherichia and carrying a recombinant DNA comprising a vector DNA and a DNA which is derived from a microorganism belonging to the genus Corynebacterium or Brevibacterium and which, upon introduction into a riboflavin-requiring microorganism, comfers on the microorganism the ability to complement its riboflavin requirement. The microorganism is cultured according to a conventional method for culturing of usual microorganisms. That is, the microorganism is cultured under the control of temperature and pH under aerobic conditions in a usual medium containing carbon sources, nitrogen sources, inorganic substances, amino acids, and vitamins. Any carbon source used may be used so long as the microorganism can assimilate it. For example, carbohydrates such as glucose, fructose, sucrose, molasses, starch, starch hydrolysates etc.; organic acids such as gluconic acid, pyruvic acid, lactic acid, acetic acid etc.; and amino acids such as glycine, glutamic acid, alanine, aspartic acid etc are mentioned. The carbon source is used preferably in a concentration of 5-40 %. As the nitrogen source, mention may be made of ammonia; various inorganic and organic ammonium salts, such as ammonium chloride, ammonium sulfate, ammonium phosphate, ammonium nitrate, ammonium carbonate, ammonium acetate etc.; nitrogen-containing organic substance, such as urea, peptone, NZ amine, meat extract, yeast extract, corn steep liquor, casein hydrolysates, fish meal or its digested product; and various amino acid, such as glycine, glutamic acid etc. These substances are employed usually in a concentration of 0.1-10 %. As the inorganic compound, mention may be made of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, magnesium sulfate, magnesium phosphate, sodium chloride, ferrous sulfate, manganese sulfate, zinc sulfate, calcium carbonate, etc. If required by the microorganisms for their growth, nutrients such as amino acids, nucleic acids, vitamins, etc., are added in a suitable amount. Where these substances are contained in other nutrients as enumerated above, their addition is not particularly required. Culturing is carried out under aerobic conditions, for example by shaking culture or by aeration-stirring culture, preferably at 20-40 °C for 24-144 hours. The pH of the medium is preferably maintained around neutrality by addition of aqueous ammonia, a urea solution, a sodium hydroxide solution, etc. The riboflavin thus formed can be quantitatively determined by high performance liquid chromatography using a reverse phase column [e.g., RP-18 (a product of Merck)] with its fluorescence intensity monitored at an emission wavelength of 530 nm and an excitation wavelength of 450 nm. Riboflavin can be recovered from the culture by a conventional purification means such as precipitation, chromatography e.g. by use of an ion-exchange resin, etc. According to the present invention, riboflavin can be efficiently produced by fermentation. EXAMPLES Hereinafter, the present invention is specifically described with reference to the following examples. Example 1 Preparation of chromosomal DNA Corynebacterium ammoniagenes KY13313 was inoculated into an AIII AG medium [10 g/l polypeptone, 10 g/l meat extract, 5 g/l yeast extract, 3 g/l sodium chloride, 30 µg/l biotin, 20 mg/l adenine and 10 g/l glycine, pH 7.2] and cultured by shaking at 30 °C for 10 hours. 0.6 g of the cultured cells was suspended in 18 ml of P-4 buffer [25mM N-tris(hydroxymethyl)methyl-2-aminoethasulfonic acid, (pH 7.6), 70 mM sodium chloride, 5 mM magnesium chloride, 5 mM calcium chloride and 1.6 M D-sorbitol], followed by addition of 2 ml of P-4 buffer containing 12 mg/ml lysozyme and 3 mg/ml acromopeptidase. The cell suspension was allowed to stand at 30 °C for 20 hours, thus giving a protoplast. The protoplast was collected by centrifugation, then suspended in TSMC buffer [50 mM Tris-HCl buffer(pH 7.5), 0.6 M sodium succinate, 10 mM magnesium chloride and 10 mM calcium chloride] and centrifuged again. The protoplast obtained as a precipitate was suspended in 12 ml of TES buffer [10 mM Tris-HCl buffer (pH 8.0), 1 mM disodium ethylenediaminetetraacetate (EDTA) and 10 mM sodium chloride] and allowed to stand at 4 °C for 30 minutes. 0.28 ml of 5 M sodium chloride and 0.04 ml of 5 mg/ml ribonuclease A (product of Sigma) were added thereto, and the mixture was allowed to stand at 37 °C for 20 minutes. Subsequently, 0.72 ml of 10 % sodium lauryl sulfate was added thereto, and the mixture was allowed to stand at 4 °C for 2 hours and then heated at 65 °C for 5 minutes. To the solution was added 13 ml of phenol saturated with TES buffer, and the mixture was thoroughly stirred. The solution was centrifuged and the aqueous layer was recovered. This procedure of extraction with phenol was repeated further 2 times, and then an equal volume of chloroform was added, thoroughly stirred, and centrifuged, thus giving an aqueous layer. 1.2 ml of 2.5 M sodium acetate was added to 12 ml of the solution thus obtained, followed by addition of 30 ml of ethanol. The chromosomal DNA thus precipitated was wound around a glass rod and then dried. The product was dissolved in 1 ml of TE buffer [10 mM Tris-HCl (pH 8.0) and one mM EDTA]. Example 2 Preparation of recombinant DNA 40 units of restriction enzyme Pst I (product of Takara Shuzo Co., Ltd.) was added to a solution containing 50 µg of the chromosomal DNA obtained in Example 1 and the mixture was allowed to stand at 37 °C for 3 hours. Separately, 40 units of restriction enzyme Pst I was added to a solution containing 50 µg of vector pCG11 DNA as constructed according to the method as described in U.S. Patent No. 4,500,640, and the mixture was allowed to stand at 37 °C for 3 hours, followed by addition of 5 units of alkaline phosphatase. The mixture was dephosphorylated at 65 °C for 1 hour. From the above two reaction solutions, chromosomal DNA and vector DNA were purified by phenol extraction and ethanol precipitation in the same manner as described above. For preparation of recombinant DNAs, 10 µg of chromosomal DNA and 20 µg of vector DNA thus treated were ligated at 16 °C for 16 hours in the presence of 700 units of T4 DNA ligase (product of Takara Shuzo Co., Ltd.) in a T4 ligase buffer [66 mM Tris-HCl buffer (pH 7.6), 6.6 mM magnesium chloride, 10 mM dithiothreitol and 0.1 mM ATP]. 40 units of restriction enzyme Bgl II (product of Takara Shuzo Co., Ltd.) was added to a solution containing 50 µg of the above chromosomal DNA, and the DNA was digested at 37°C for 3 hours in the same manner as described above. Separately, 40 units of restriction enzyme Bgl II was added to a solution containing 50 µg of the vector pCG11 DNA, and then the vector was digested at 37 °C for 3 hours. After addition of 5 units of alkaline phosphatase, the mixture was dephosphorylated at 65 °C for one hour. From the resulting two reaction solutions chromosomal DNA and vector DNA were purified by phenol extraction and ethanol precipitation in the same manner as described above. For preparation of recombinant DNAs, 10 µg of chromosomal DNA and 20 µg of vector DNA thus treated were ligated at 16 °C for 16 hours in the presence of 700 units of T4 DNA ligase (product of Takara Shuzo Co., Ltd.) in the T4 ligase buffer. Example 3 Acquisition of a riboflavin-requiring strain from Corynebacterium ammoniagenes Riboflavin-requiring strain RK122 was obtained from Corynebacterium ammoniagenes KY13313 in the following manner. Corynebacterium ammoniagenes KY13313 was cultured at 30 °C for 7 hours in a medium having the same composition as AIII AG medium except that glycine is not contained, and then mutated at 30 °C for 90 min. with 100 µg/ml N-methyl-N'-nitro-nitrosoguanidine. The cells were collected, washed, and inoculated into a riboflavin-free minimum liquid medium [20 g/l glucose, 0.1 g/l KH2PO4, 0.3 g/l K2HPO4, 0.3 g/l MgSO4.7H2O, 0.01 g/l CaCl2.2H2O, 10 mg/l FeSO4.7H2O, 1 mg/l ZnSO4.7H2O, 4 mg/l MnSO4.4-6H2O, 0.2 mg/l CuSO4.5H2O, 40 mg/l L-cysteine, 10 mg/l vitamin Bl, 20 mg/l Ca-D-pantothenic acid, 60 µg/l biotin, 3 g/l NH4Cl, 2 g/l urea, 50 mg/l adenine, pH 7.2], followed by culturing at 30°C. 100 U/ml penicillin G was added at the logarithmic growth phase, followed by additional 16-hour culturing at 30 °C so that the riboflavin-requiring strains were concentrated. Riboflavin-requiring strain RK122 capable of growing only in a riboflavin-containing minimum medium was obtained by replica plating on a minimum agar medium with a without 5 mg/l riboflavin [a minimum liquid medium containing 2 % agar]. Example 4 Transformation of the riboflavin-requiring strain Corynebacterium ammoniagenes RKIZZ with the recombinant DNA According to the electroporation method [W. J. Dower et al., Nucleic Acids Research, 16 , 6127 (1988)], the riboflavin-requiring strain was transformed with the recombinant DNA in the following manner. Corynebacterium ammoniagenes RK122 was cultured at 30 °C for 5 hours in an AIII AG medium, then washed with 15 % glycerol solution (cooled on ice) containing 272 mM sucrose, and suspended in the same solution as mentioned above. The resulting cell suspension was mixed with a solution of the Pst I-digested recombinant DNA obtained in Example 2, and transformation was carried out with a gene pulser (Bio-Rad Laboratories, Richmond, CA, USA) according to the electroporation method (a voltage of 2.5 kV, capacity of 25 µF, and resistance of 200 Ω). Then, the cell suspension was plates onto a minimum agar medium containing 150 µg/l spectinomycin, and cultured at 30 °C for 3days. Corynebacterium ammoniagenes RK122/pFM21 (being resistant to spectinomycin and requiring no riboflavin) was related from colonies occurring on the agar plate medium. According to the method as described above, transformant RK122/pFM41 was obtained using the Bgl II-digested recombinant DNA obtained in Example 2. Example 5 Extraction of plasmids from the transformants The transformants RK122/pFM21 and RK122/pFM41 were cultured respectively in 250 ml of AIII AG medium containing spectinomycin. According to the method as described in Example 2, plasmid DNAs, each about 100 µg, were obtained respectively from the culture of RK122/pFM21 and RK122/pFM41, and these plasmids were designated pFM21 and pFM41, respectively. FIG. 1 shows restriction enzyme maps for the recombinant plasmids pFM21 and pFM41 where the inserted fragments are 4.7 and 4.2 kb, respectively. In pFM41 set forth in FIG. 1, the Bgl II site in the parenthesis could not be cleaved with Bgl II owing to some possible reasons such as microorganism upon the cleavage of the chromosomal DNA or the treatment of the vector DNA with phosphatase. The 2.7 kb fragment, excised with restriction enzymes Pst I and Bgl II, was contained in both plasmids. Example 6 Measurement of riboflavin synthase activity According to the method as described in Method in Enzymology 122, 192 (1986), the transformants KY13313/pCG11, KY13313/pFM21, and KY13313/pFM41 were measured for their riboflavin synthase activity. The result indicated that the transformants carrying recombinant DNAs pFM21 and pFM41 had enzyme activities 3.8 and 1.8 times respectively as high as that of the transformant carrying the vector pCG11 only. Example 7 Measurement of guanosine triphosphate cyclohydrolase activity According to the method as described in Archives of Microbiology, 124, 255 (1980), the transformants KY13313/pCG11, KY13313/pFM21 and KY13313/pFM41 were measured for their guanosine triphosphate cyclohydrolase activity. The result indicated that the transformants carrying pFM21 and pFM41 exhibited 6.1- and 4.3-fold high enzyme activities respectively as compared with that of the transformant carrying the vector pCG11 only. Example 8 Analysis of the DNA capable of conferring on the riboflavin-requiring strain the ability to complement its riboflavin requirement The 5.6 kb Sal I- Sal I fragment (containing the 2.7 kb fragment in common) inserted into plasmid pFM21 and pFM41 was determined for its DNA nucleotide sequence by the dideoxy method [Messing, J., Method in Enzymology, 101 , 20 (1983)]. The result is set out in SEQ. ID No. 1. Example 9 Introduction of the plasmid into Escherichia coli A solution containing 1 µg of plasmid pFM21 DNA obtained in Example 5 was digested at 37 °C for 1 hour with 2 units of restriction enzyme Pst I. Then, a 4.7 kb fragment was isolated from the digested product by agarose gel electrophoresis. Separately, 0.5 µg of vector pUC19 (product of Takara Shuzo Co., Ltd.) was digested at 37 °C for 1 hour with 2 units of Pst I and then dephosphorylated with alkaline phosphatase in the same manner as described in Example 2. The vector DNA thus obtained was then subjected to phenol extraction and ethanol precipitation. The above pFM21-derived DNA fragment, 100 ng, was mixed with 50 ng of the above vector DNA. The mixture was ligated at 16 °C for 2 hours in the presence of 100 units of T4 ligase in the T4 ligase buffer. The resulting recombinant DNA was used for transformation of E. coli JM105 according to the method as described by Cohen et al. [Proc. Natl. Acad. Sci., USA, 69 , 2110 (1979)], and the cells were plated on an LB agar medium [a medium prepared by adding 1.5 % agar to an LB liquid medium (10 g/l bactotrypton, 5 g/l yeast extract, 5 g/l sodium chloride, pH 7.2)) containing 100 mg/l of ampicillin, 0.1 mM isopropylthiogalactoside and 0.004 % of 5-bromo-4-chloto-3-indoyl-β-D-galactopyranoside. From the resulting white transformant, plasmid DNA was isolated and purified according to the method of Maniatis et al. [Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory (1982)]. This plasmid DNA was analyzed for its structure by a digestion with various restriction enzymes. As a result, the plasmid DNA was found to have the structure set forth in FIG. 2 where a pFM21-derived DNA fragment containing the genes encoding the enzymes involved in the synthesis of riboflavin has been inserted downstream of pUC19 lac promoter, and this plasmid DNA was designated pFM201. Example 10 Production of riboflavin by use of an Escherichia coli transformant A transformant, Escherichia coli JM105/pFM201 obtained in Example 9 was inoculated into 8 ml of LB liquid medium containing 100 mg/l ampicillin, followed by culturing at 30 °C for 16 hours. The culture solution thus obtained was inoculated into 8 ml of minimum medium containing 100 mg/l ampicillin (3 g/l KH2PO4, 5 g/l NaCl, 1 g/l NH4Cl, 6 g/l NaHPO4, 0.25 g/l MgSO4.7H2O, 4 mg/l vitamin B1 and 3 g/l glucose) and cultured at 30 °C for 24 hours. The amount of riboflavin accumulated in the culture solution was 14.4 mg/l. In contrast, 0.3 mg/l of riboflavin was accumulated in the culture obtained under the same conditions with respect of E . coli JM105/pUC19 carrying only the vector plasmid pUC19. Example 11 Production of riboflavin by use of a Corynebacterium ammoniagenes Transformant Corynebacterium ammoniagenes KY13313 was transformed in the method described in Example 4 with the pFM41 DNA obtained in Example 5. A suspension of the cells was plated on a medium containing 150 µg/ml of spectinomycin and cultured at 30 °C for 3 days. A spectinomycin-resistant transformant, Corynebacterium ammoniagenes FM41 (FERM BP-4003), was obtained from the growing colonies. Corynebacterium ammoniagenes FM41 was inoculated into 8 ml of seed medium [10 g/l polypeptone, 10 g/l meat extract, 5 g/l yeast extract, 3 g/l sodium chloride, 30 µg/l biotin, 20 mg/l adenine and 150 mg/l spectinomycin, pH 7.2] in a test tube. The cells were then cultured at 30 °C for 24 days by shaking. 1.5 ml of the culture was inoculated into 30 ml of fermentation medium (Table 1) put in a 300 ml Erlenmeyer flask. After 72 hours of shaking culture at 30 °C, riboflavin was accumulated in an amount of 620 mg/l in the culture. In contrast, riboflavin was accumulated in an amount of 35 mg/l in the culture obtained under the same conditions with respect of Corynebacterium ammoniagenes KY13313 carrying only the vector plasmid pCG11. component content polypeptone 10 g/l glucose 80 g/l KH2PO4 1 g/l K2HPO4 3 g/l MgSO4.7H2O 1 g/l CaCl2.2H2O 0.1 g/l FeSO4.7H2O 10 mg/l ZnSO4.7H2O 1 mg/l MnSO4.4-6H2O 4 mg/l CuSO4.5H2O 0.2 mg/l L-cysteine 40 mg/l vitamin B1 10 mg/l Ca-D-pantothenic acid 20 mg/l biotin 60 µg/l (NH4)2SO4 5 g/l urea 5 g/l adenine 100 mg/l spectinomycin 150 mg/l CaCO3 20 g/l pH 7.2 Example 12 Difference from Bacillus -derived gene 5 units of restriction enzyme Pst I was added to a solution containing 2 µg of chromosomal DNA from Bacillus subtilis 168, and the DNA was digested for 5 hours at 37 °C. Subsequently, the DNA fragments were subjected to agarose gel electrophoresis, immobilized onto a nylon filter, and subjected to Southern hybridization with a 1 kb Xho I- Hind III fragment as a probe derived from pFM201, using a nonradio system DNA labeling and detection kit produced by Boehringer Mannheim Yamanouchi Co., Ltd. As a result, no hybridization was observed between the probe and the chromosomal DNA from the strain 168. SEQUENCE LISTING SEQ ID NO: 1 SEQUENCE LENGTH: 5589 SEQUENCE TYPE: nucleic acid TOPOLOGY: linear MOLECULAR TYPE: genomic DNA HYPOTHETICAL: NO ANTISENSE: NO ORIGINAL SOURCE ORGANISM: Corynebacterium ammoniagenes SEQUENCE:

Claims: An isolated DNA which is derivable from a microorganism belonging to the genus Corynebacterium and which, upon introduction into a riboflavin-requiring host microorganism, is capable of conferring on the microorganism the ability to complement its riboflavin requirement, the DNA encoding at least guanosine triphosphate cyclohydrolase and riboflavin synthase. A DNA according to claim 1, which has the nucleotide sequence set forth in SEQ. ID No. 1 or a partial sequence thereof. A DNA according to claim 2, which is the 2.7 kb DNA fragment from position 1476 to position 4164 in the nucleotide sequence set forth in SEQ. ID No. 1. A DNA according to any one of the preceding claims, which is derivable from Corynebacterium ammoniagenes . A recombinant DNA comprising a DNA as defined in any one of the preceding claims and a vector DNA. A microorganism carrying a recombinant DNA as defined in claim 5. A microorganism according to claim 6, which belongs to the genus Corynebacterium, Brevibacterium or Escherichia. A process for producing riboflavin, which process comprises culturing in a medium a microorganism as defined in claim 6 or 7 until riboflavin has accumulated in the culture, and recovering the riboflavin therefrom.

Inventors: KOIZUMI SATOSHI, TESHIBA SADAO, YONETANI YOSHIYUKI, KOIZUMI, SATOSHI, TESHIBA, SADAO, YONETANI, YOSHIYUKI
Applicants: KYOWA HAKKO KOGYO KK, KYOWA HAKKO KOGYO CO., LTD.
Application year: 1993
Main classification: C12P25
IPC codes: C12N15, C12P25, C12N1