INCORPORATION OF [METHYL-H-3]THYMIDINE BY OBLIGATE AND FACULTATIVE ANAEROBIC-BACTERIA WHEN GROWN UNDER DEFINED CULTURE CONDITIONS

Incorporation of [methyl-H-3]thymidine into bacterial DNA was determin ed for a range of axenic anaerobic bacterial cultures: fermentative he terotrophs, sulphate-reducing bacteria, purple sulphur bacteria, aceto gens and methanogens. Anaerobically growing Bacillus sp. and the oblig ate aerobe Thiobacillus ferrooxidans were also investigated. Actively growing cultures of sulphate-reducing bacteria belonging to the genera Desulfovibrio, Desulfotomaculum, Desulfobacter, Desulfobotulus and De sulfobulbus, purple sulphur bacteria (Chromatium vinosum OP2 and Thioc apsa roseopersicina OP1), methanogens (Methanococcus GS16 and Methanos arcina barkeri) and an acetogen (Acetobacterium woodii) did not incorp orate [methyl-H-3]thymidine into DNA. The only obligate anaerobes in w hich thymidine incorporation into DNA could be unequivocally demonstra ted were members of the genus Clostridium. Anaerobically growing Bacil lus 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 phototroph s within sediments are unable to incorporate [Methyl-H-3]thymidine int o DNA, although some obligate and facultative anaerobes can. Variabili ty in thymidine incorporation amongst pure culture isolates indicates that unless existing techniques can be calibrated to take this into co nsideration then productivity estimates in both aerobic and anaerobic environments may be greatly underestimated using the [methyl-H-3]thymi dine technique.