Marine bacterioplankton abundances and distributions
Robert M. Morris, Ph.D.
Wednesday, February 2, 2005
Pacific Forum – 3:00 p.m.
Although gene cloning studies have greatly expanded our view of microbial diversity in the oceans, they are not quantitative and seldom provide phenotypic information. Direct cell counts and community structural analyses can be used to quantify lineage abundances and correlate distribution patterns with oceanographic and biogeochemical processes. Direct SAR11 and SAR202 cell counts provided the first quantitative evidence indicating that these bacterioplankton lineages were stratified. Members of the SAR11 clade dominated ocean surface waters and Chloroflexi-related SAR202 cells were abundant throughout the mesopelagic zone. Community structural analysis of amplified 16S rRNA gene fragments supported SAR11 and SAR202 cell distributions and identified spatial and temporal variability among specific lineages and subgroups. Fragments attributed to SAR11 subgroup Ia increased during summer months, suggesting that members of this subgroup contain adaptations similar to phototrophic bacterioplankton, and fragments attributed to OCS116 increased following deep convective mixing, indicating a role in DOC dynamics at BATS.Non-metric multidimensional scaling (NMS) of bacterial 16S rDNA terminal restriction fragments collected at the BATS site between 1992 and 2002. Sample groupings indicate bacterioplankton variability in post-mixing (February to May), summer (June to September), and winter (October to January) time periods for complete, surface, and 200 m T-RFLP data sets. Larger symbol sizes correspond to increases in the relative abundance of SAR11 subgroup Ia and OCS116 fragments. February 200m (D92) exhibited strong increases in fragments contributing to post-mixing groupings and was selected for clone library analysis.