SS2.01 Effects of Biotic Interactions on the Structure and Function of Microbial Food Webs
Date: Wednesday, June 12, 2002
Time: 11:30:00 AM
Location: Saanich
 
del GiorgioPA, Dépt des sciences biologiques, Université du Québec à Montréal, Montréal, Canada, del_giorgio.paul@uqam.ca
Maranger, R, , Institute of Ecosystems Studies, Millbrook, USA, MarangerR@ecostudies.org
Bird, D, , Dépt des sciences biologiques, Université du Québec à Montréal, Montréal, Canada, bird.david@uqam.ca
 
INTERACTIONS BETWEEN GRAZING AND UV INFLUENCE THE DISTRIBUTION OF SINGLE-CELL ACTIVITY IN LAKE BACTERIOPLANKTON
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Selective grazing by protozoans and UV radiation are factors known to influence the functioning of bacterioplankton assemblages, but the interaction between these factors has not been investigated. We explored the combined effects of UV and grazing on leucine uptake and on the distribution of highly active, and dead (or injured) bacterial cells, in dialysis bags experiments carried out in a colored lake. Highly active bacteria are those reducing CTC (CTC+), and injured bacteria are those taking up the exclusion nucleic acid stain TOPRO-1. Leucine uptake in the bags and ambient water was unrelated to total cell abundance, but correlated with %CTC+ cells. The %CTC+ cells in the ambient water and in most treatments ranged from 10 to 35%, and bur reached 65% in bags without grazers and no UV exposure. Grazer-free bags that were incubated at subsurface light did not develop increased proportions of highly active cells, but rather had a high proportion of injured bacteria (TOPRO+). The results suggest that UV may interact with grazing to determine the proportion of active and injured cells of epilimnetic bacterioplankton.