[Effect of a corrinoid on Methanosarcina barkeri DNA synthesis].

Methanosarcina barkeri is capable of synthesizing large amounts of corrinoids, compounds of the vitamin B12 group, although not cobalamin. In the present work, exogenous cobalamin was demonstrated to upregulate DNA synthesis in M. harkeri cell suspensions incubated under air. The effect is similar to the one in Propionibacterium freudenreichii cells, though less pronounced. The growth of the archaeon under anaerobic conditions was shown to be suppressed by cobalamin and 5,6-dimethylbenzimidazole. The data obtained suggest the presence of a corrinoid-dependent ribonucleotide reductase in the archaeon cells which provides for deoxyribose precursors for DNA biosynthesis independently of the presence of molecular oxygen in the medium. Growth suppression under anoxic conditions by cobalamin and 5,6-dimethylbenzimidazole may be due to a decrease in the concentration of factor III, a polyfunctional corrinoid dominating in M. barkeri cells.