BACTERIAL [METHYL-H-3]THYMIDINE INCORPORATION IN SUBSTRATE-AMENDED ESTUARINE SEDIMENT SLURRIES

Five different bacterial communities were enriched in substrate-amende d slurries of sediment from the Tay Estuary, Scotland. During incubati on of the slurries, concentrations of volatile fatty acids, sulphate, sulphide and methane were monitored to clearly define the activity of the stimulated populations. An aerobic population, a 'microaerophilic' population and three anaerobic populations (fermentative heterotrophs , sulphate-reducing bacteria and methanogens plus acetogens) were esta blished to reflect community growth and metabolism both in surface oxi c and deeper anoxic layers. Similar numbers of cells involved in divis ion were observed in all five slurries, demonstrating the potential fo r bacterial production. Thymidine incorporation rates in glucose-stimu lated slurries under both aerobic and fully anaerobic conditions were similar, confirming the ability of fermentative anaerobic heterotrophs to incorporate [methyl-H-3]thymidine into DNA during growth. Although anaerobic communities of sulphate-reducing, acetogenic plus methanoge nic bacteria were stimulated and actively growing, they did not incorp orate [methyl-H-3]thymidine into DNA. Since the thymidine technique do es not measure the growth of these important groups, calculated produc tivity values based upon thymidine incorporation within anoxic sedimen t systems will be substantially underestimated, even if growth substra tes are not limiting.