MEASUREMENT OF BACTERIVORY BY PROTISTS IN OPEN-OCEAN WATERS

Protozoa are the main consumers of heterotrophic bacteria in aquatic h abitats. The numbers of these bacteria and protozoa in oligotrophic ar eas of the open ocean are low, and current methods lack the sensitivit y to assess rates of bacterivory in such waters. A new method is propo sed for estimating bacterivory on dual radioactively labelled natural bacteria using living ambient prey bacteria and separation of predator s from prey by fractionation. This approach is sufficiently sensitive to measure the consumption of less than 1% of the labelled bacteria du ring a 13-h incubation period. When tested on samples collected from 2 7 stations in mesotrophic and oligotrophic regions of the North and So uth Atlantic Oceans, about 17% of metabolically active bacteria were g razed per day and about 60% of consumed prey biomass labelled with C-1 4-leucine was retained by the predators. (C) 1998 Federation of Europe an Microbiological Societies. Published by Elsevier Science B.V. All r ights reserved.