del Giorgio, P. Horn Point Lab, University of Mayland Center for Environmental Science,

Bacterioplankton are composed of subpopulations of cells in different physiological states, including dead, dormant and highly active cells. From theoretical considerations it is expected that bacterial growth efficiency (BGE) should differ among these subpopulations. The community BGE should therefore be a function of the proportions of cells in various physiological states. I tested this hypothesis in samples from the Delaware Bay and surrounding tidal marshes. BGE was calculated from bacterial respiration (O2 consumption) and production (leucine uptake) in 8 hour incubations of filtered water. Single-cell activity in these samples was determined using the CTC method: cells with an active electron transport system will reduce CTC to its fluorescent formazan, and these cells were enumerated using flow cytometry. Single-cell activity varies continuously, so no method can provide an absolute distinction between active and inactive cells, but there is evidence that CTC detects the most active cells in the assemblage. There was a significant positive relationship between bulk BGE and the proportion of highly active (CTC+) bacteria, in spring, summer and fall. These results suggest that factors that alter the proportion of active and inactive cells, such as viral infection, protozoan grazing, and other food web interactions might strongly influence BGE in aquatic systems.
Day: Monday, Feb. 1
Time: 02:45 - 03:00pm
Location: Sweeney Center
Code: SS41MO0245S