Activity of marine bacteria under incubated and in situ conditions

We evaluated the extent to which the average metabolic activity of open oce an bacterioplankton changed during 2 to 3 d incubations of 1 mu m filtered seawater at in situ temperature. Indices of bacterial activity during incub ation experiments were compared to those of in situ bacterioplankton, which were repeatedly sampled at each oceanic site. Indices included: total and cell-specific incorporation rates of tritiated leucine ([H-3]-Leu) and thym idine ([H-3]-TdR), ratio of Leu to TdR incorporation, and percentage of hig hly active cells as determined by detectable reduction of the fluorogenic d ye, 5-cyano-2,3-ditolyl tetrazolium chloride (CTC). Patterns of change in m etabolic activity were similar for experiments with water collected in 3 re gions: midshelf, slope, and offshore, off the Oregon coast, USA, and incuba ted at in situ temperatures of 9.5 to 18 degrees C. At the beginning of the experiments, cell-specific incorporation rates of [H-3]-Leu and [H-3]-TdR were lower compared to in situ rates, but after 19 to 28 h, incorporation r ates of [H-3]-Leu and [H-3]-TdR increased dramatically, by more than an ord er of magnitude, compared to in situ activity. When scaled to the abundance of CTC positive (CTC+) cells, rates of Leu and TdR incorporation were 2.8- to 8.1-fold higher during the incubations compared to activity of in situ CTC+ cells. In this study, marine bacteria in 1 mu m, incubated filtrate ex hibited a much larger Variation in metabolic activity than did in situ bact erioplankton. In addition, the proportion of CTC+ cells was closely related to cell-specific rates of Leu and TdR incorporation.