COMPARISON OF DNA AND PROTEIN-SYNTHESIS RATES OF BACTERIAL ASSEMBLAGES BETWEEN CORAL-REEF WATERS AND PELAGIC WATERS IN TROPICAL OCEAN

DNA and protein synthesis activities of Pacific bacterial assemblages in coral reefs of Ponape Island (eutrophic water), Majero Atoll (mesotrophic water) and pelagic waters (oligotrophic water) were estimated by measuring incorporation rates of H-3-thymidine and H-3-leucine into the TCA-insoluble fraction (TdR(DNA), Leu(prot)). Bacterial production rates estimated by TdR(DNA) were 0.14 to 0.94 (average 0.52) x 10(4) cells ml-1 h-1 in the pelagic water and 0.93 to 26 (average 10) x 10(4) cells ml-1 h-1 in the eutrophic water. Obligate oligotrophs predominated in the pelagic water, but facultative oligotrophs were dominant in the eutrophic water. In the eutrophic water protein synthesis rates expressed by Leu(prot) were positively correlated to DNA synthesis rates expressed by TdR(DNA); however, in the oligotrophic pelagic water, there was no such correlation. Uptake activities of leucine at low concentration were maintained at relatively high levels in the oligotrophic water although H-3-thymidine incorporation rates were extremely low. From these results, it is suggested that bacterial assemblages in oligotrophic waters have an uptake system with high affinity to substrates and utilize metabolic energy to achieve substrate uptake and protein synthesis preferentially to DNA synthesis and reproduction, and that these properties were mostly due to obligately oligotrophic bacteria adapted to a low nutrient environment.