Riemann, L. Freshwater Biological Laboratory, University of Copenhagen, flabms@inet.uni-c.dk
Steward, G. Monterey Bay Aquarium Research Institute, gsteward@mbari.org
Azam, F. Marine Biology Research Division, Scripps Institution of Oceanography, University of California, fazam@ucsd.edu

We examined bacterial species succession, enzymatic activities, and carbon dynamics during a marine diatom bloom. The experiments were carried out in four, 200 liter laboratory mesocosms using water collected at Scripps Pier, La Jolla, California. Bacterial community genomic DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. Dominant bands from the gels were excised, cloned and sequenced. The majority of the 16 sequenced phylotypes were related to Alpha-Proteobacteria, Cytophagales or oxygenic phototrophs. The diatom bloom was dominated by Thalassiosira sp. As the bloom peaked after nine days, a pronounced decline in bacterial abundance (2.8 to 0.75 million per ml) and a disappearance of three dominant phylotypes was observed. This was presumably caused mainly by virus infection. At the same time new phylotypes appeared and bacterial production, abundance and enzyme activities shifted from being predominantly associated with the size-fraction <1.0 micrometer towards the >1.0 micrometer size-fraction. Size fractionation suggested that colonization of particles was mainly by specialized Alpha Proteobacteria and Cytophagales related species. The prevalence of members of Cytophagales during the different stages of the diatom bloom suggests that these bacteria have a flexible growth strategy and may thrive in both free-living and particle-associated communities.
Day: Tuesday, Feb. 2
Time: 11:45 - 12:00pm
Location: Hilton of Santa Fe
Code: SS40TU1145H