OLIGOTROPHIC PROPERTIES OF HETEROTROPHIC BACTERIA AND INSITU HETEROTROPHIC ACTIVITY IN PELAGIC SEAWATERS

The distribution of heterotrophic bacteria in polluted coastal and unpolluted pelagic seawaters was studied using a 14C-MPN method with either five of seven kinds of 14C-organic compounds as substrates. The total number of heterotrophic bacteria in pelagic waters ranged from 9.2 × 103 to 5.4. ¢ 104 cell/ml and more than 85% of the heterotrophic bacteria were represented by obligate oligotrophs. In coastal waters, the number of heterotrophs was one order of magnitude higher (av. 3.5 ¢ 105 cells/ml), and eutrophic and facultatively oligotrophic bacteria were predominant. Oligotrophs in pelagic waters had a high specificity for the utilization of amino acids, especially glycine, and acetate-utilizing bacteria were scarce. The in situ maximum uptake rates of glutamate and glycine were much higher than those of glycolate and acetate. Acetate uptake rates were extremely low or not detectable in pelagic waters. The specificity of uptake kinetics is assumed to depend on the existence of obligate oligotrophs as dominant bacteria in pelagic seawater. © 1990.