Fundamental role of cobalamin biosynthesis in the developmental growth of Streptomyces coelicolor A3 (2).

Cobalamin (Cbl) (synonym, vitamin B12) is the cobalt-containing cofactor produced only by some prokaryotes. Streptomyces is an effective Cbl producer. To study the role of Cbl production in Streptomyces, a knockout mutant for Cbl biosynthesis (cob) was generated in Streptomyces coelicolor A3 (2). The growth of the mutant was similar to that of the wild type in a rich medium, but inhibited in minimal medium, suggesting the involvement of Cbl in some step of primary metabolism. Methionine synthesis catalyzed by MetH, the Cbl-dependent methionine synthase, is a candidate. However, supplementing the minimal medium with methionine did not rescue the growth of the cob mutant, indicating that the availability of Cbl affects another primary function. Transcriptional analysis confirmed that the mutant induced metE encoding an alternative Cbl-independent methionine synthase, probably due to the Cbl-dependent riboswitch mechanism. The cob mutant produced low levels of pigment antibiotics and formed fewer aerial mycelium and spores in a rich medium, suggesting that a Cbl-dependent mechanism controls development. A similar developmental defect was observed for a knockout mutant for SCO4800, encoding the putative Cbl-dependent isobutyryl-CoA mutase (Icm) small subunit. Since the knockout of the Icm large subunit (SCO5415) did not affect the developmental phenotype, SCO4800 likely regulates development independently from SCO5415. Effective Cbl production is fundamental to the diverse functions underlying the complex developmental life cycle of S. coelicolor A3 (2).