Population dynamics of Cytophaga-Flavobacteria during marine phytoplankton blooms analyzed by real-time quantitative PCR

We analyzed the dynamics of the Cytophaga-Flavobacterium (CF) cluster during a Thalassiosira sp.-dominated diatom bloom in a mesocosm and a coastal bloom of the dinoflagellate Lingulodinium polyedrum using quantitative (TaqMan) PCR. Particle colonization was tracked by quantifying CF small subunit (SSU) rDNA copies as a percentage of total bacterial SSU rDNA copies in operationally defined free-living (ca. 1.0 mu m) size fractions. During both blooms, the percentage of CF rDNA in the free-living fraction was greater than in the particle-associated fraction, yet ranged widely from almost undetectable to 10-40% of total SSU rDNA. The percentage of CF rDNA copies in the attached fraction was low overall (<= 3.2 % of total), except at the chl a peak of the dinoflagellate bloom when CF rDNA copies comprised > 50 % of the total bacterial SSU rDNAs in that fraction. In addition, the timing of peaks in attached CF differed between blooms, occurring at the peak in chlorophyll a for the dinoflagellate bloom, but during the detrital phase of the diatom bloom. Our data suggests that different bloom types may encourage different attachment responses by CF and indicate that high abundance of CF during a phytoplankton bloom is transient in nature, with shifts in abundance and group composition occurring on the order of 1 d to a few days.