METABOLIC-ACTIVITY OF BACTERIOPLANKTON COMMUNITIES ASSESSED BY FLOW-CYTOMETRY AND SINGLE CARBON SUBSTRATE UTILIZATION

During the summer of 1994, bacterioplankton abundance and metabolism w ere examined in seawater from Bedford Basin, Nova Scotia, Canada. Two new methods were applied to independently assess metabolic activity: ( 1) flow cytometric analysis of bimodal nucleic acid distributions in b acterioplankton stained with a novel fluorescent dye, and (2) utilizat ion of single carbon substrates in Biolog GN Microplates(TM). Both set s of results were compared to bacterial production estimates obtained using a standard technique for H-3-thymidine and H-3-leucine incorpora tion. Flow cytometry quantified the relative abundance of the bacterio plankton cells with a high apparent nucleic acid content, which was ex pressed as an active cell index (ACI) of dividing and/or actively meta bolizing cells. The ACI was positively correlated with sole carbon sou rce utilization at 1, 5 and 10 m (p < 0.05). Variations in ACI and sol e carbon source utilization followed trends similar to, but could not be directly correlated with, bacterial production throughout the summe r period. The new methods provided information that could not be obtai ned using the standard techniques for bacterial production. Instead, t hey yielded new and complementary information on the metabolic state o f dividing and/or metabolizing cells and insight into the regulation o f bacterial production.