Woods Hole Oceanographic Institution

Matthew First

»Environmental factors shaping microbial community structure in salt marsh sediments
»The model high molecular weight DOC compound, dextran, is ingested by the benthic ciliate, Uronema marinum, but does not supplement ciliate growth
»Microzooplankton growth and trophic interactions and their effects on herbivory in coastal and offshore environments
»Protistan bacterivory and benthic microbial biomass in an intertidal creek mudflat
»Microzooplankton growth patterns across natural and experimental trophic gradients: Implications for herbivory studies
»Growth and grazing rates of bacteria groups with different apparent DNA content in the Gulf of Mexico

Jochem, F.J., Lavrentyev, P.J. and M.R. First , Growth and grazing rates of bacteria groups with different apparent DNA content in the Gulf of Mexico , Marine Biology, 2004

Growth rates and grazing losses of bacterioplankton were assessed by serial dilution experiments in surface waters in the Mississippi River plume, the northern Gulf of Mexico, a Texas coastal lagoon (Laguna Madre), southeast Gulf of Mexico surface water, and the chlorophyll subsurface maximum layer in the southeast Gulf of Mexico. Bacteria were quantified by flow cytometry after DNA staining with SYBR Green, which allowed for discrimination of growth and grazing rates of four bacteria subpopulations distinguished by their apparent DNA content and cell size (light scatter signal). Total bacteria growth rates (0.2-0.9 day-1) were mostly balanced by grazing losses, resulting in net growth rates of -0.18 to 0.45 day-1. Growth rates of DNA subpopulations varied within experiments, sometimes substantially. In most, but not all, experiments, the largest bacteria with highest DNA content exhibited the highest growth rates, but a relationship between DNA content and growth rates or grazing losses was absent. Small bacteria with the lowest DNA content showed positive growth rates in most experiments, sometimes higher than growth rates of bacteria containing more DNA, and were grazed upon actively. Low-DNA bacteria were not inactive and were an integral part of the microbial food web.

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