Incorporation of [methyl-3H]thymidine by obligate and facultative anaerobic bacteria when grown under defined culture conditions

Incorporation of [methyl-3H]thymidine into bacterial DNA was determined for a range of axenic anaerobic bacterial cultures: fermentative heterotrophs, sulphate-reducing bacteria, purple sulphur bacteria, acetogens and methanogens. Anaerobically growing Bacillus sp. and the obligate aerobe Thiobacillus ferrooxidans were also investigated. Actively growing cultures of sulphate-reducing bacteria belonging to the genera Desulfovibrio, Desulfotomaculum, Desulfobacter, Desulfobotulus and Desulfobulbus, purple sulphur bacteria (Chromatium vinosum OP2 and Thiocapsa roseopersicina OP1), methanogens (Methanococcus GS16 and Methanosarcina barkeri) and an acetogen (Acetobacterium woodii) did not incorporate [methyl-3H]thymidine into DNA. The only obligate anaerobes in which thymidine incorporation into DNA could be unequivocally demonstrated were members of the genus Clostridium. Anaerobically growing Bacillus sp. also incorporated thymidine. These data demonstrate that pure culture representatives of major groups of anaerobic bacteria involved in the terminal oxidation of organic carbon and anoxygenic phototrophs within sediments are unable to incorporate [methyl-3H]thymidine into DNA, although some obligate and facultative anaerobes can. Variability in thymidine incorporation amongst pure culture isolates indicates that unless existing techniques can be calibrated to take this into consideration then productivity estimates in both aerobic and anaerobic environments may be greatly underestimated using the [methyl-3H]thymidine technique.