Abstract: There is provided an economical, efficient and industrially useful method of producing vitamin B.sub.12 which comprises cultivating a microorganism belonging to Rhizobium cobalaminogenum FERM BP-4429 which is capable of producing vitamin B.sub.12 in a culture medium and recovering the vitamin B.sub.12. The microorganism is isolated from soil and has no formation of acids from L-arabinose. Further, there are no straight chain fatty acids 21:1 or 19:0.

Abstract: There is provided an economical, efficient and industrially useful method of producing vitamin B.sub.12 which comprises cultivating a microorganism belonging to Rhizobium cobalaminogenum which is capable of producing vitamin B.sub.12 in a culture medium to produce vitamin B.sub.12 and recovering the produced vitamin B.sub.12. There are also provided a microorganism belonging to Rhizobium cobalaminogenum which is capable of producing vitamin B.sub.12 and a microorganism Rhizobium cobalaminogenum 27B74 (FERM BP-4429).

Abstract: Uridine is produced by cultivating in a culture medium a uridine-producing microorganism, which belongs to the genus Bacillus and which is deficient in uridine nucleoside phosphorylase activity and is resistant to a pyrimidine analogue, and recovering the accumulated uridine. This method has the advantage of substantially avoiding the by-production of uracil and uridylic acid.

Abstract: Cytidine and/or deoxycytidine are produced at high yields by culturing cytidine deaminase activity-defective microbes of the genus Bacillus, which have resistance to pyrimidine analogs and with the ability to produce cytidine and/or deoxycytidine in a medium.

Abstract: Method of producing inosine and/or guanosine by culturing an inosine and/or guanosine-producing mutant of the genus Bacillus which requires adenine for growth and is resistant to an antifolate. Thus, inosine and/or guanosine can be produced in much greater yields, compared with known methods.

Abstract: A method of producing guanosine using an adenine-requiring microorganism, in which method the amount of the adenine-containing material to be added to the initial medium is restricted to not more than 50% of the required amount and, after the adenine-containing material added to the initial medium has been consumed almost completely, the remainder of the required amount is added intermittently or continuously.

Abstract: In a fermentation procedure for the production of nucleosides i.e. inosine and/or guanosine using an adenine-requiring microorganism, the fermentation is carried out by allowing a source of adenine to be present in the medium in an excess amount over the amount of adenine that would be conductive to a maximum yield of inosine and/or guanosine in aerobic culture using ordinary air, and cultivating the microorganism while an oxygen-rich gas is bubbled into the medium. Thus, inosine and/or guanosine are accumulated in high yield in the fermentation broth.

Abstract: A method of producing inosine and/or guanosine comprising cultivating a microorganism in a medium containing a carbohydrate, in which method a carbohydrate is added either continuously or intermittently to the medium when and in the state that the concentration of the carbohydrate in the medium is less than about 1 percent so that the carbohydrate concentration of the medium is maintained below about 1 percent.

Abstract: D-Ribose is produced by cultivating a strain belonging to the genus Bacillus, which lacks sporulation ability or has high 2-deoxy-D-glucose-oxidizing activity or has both of these two properties and also lacks at least one of transketolase and D-ribulose phosphate 3-epimerase, to cause said strain to elaborate and accumulate a large amount of D-ribose. The thus accumulated D-ribose can be recovered in good yield.