Species-specific patterns in the vulnerability of carbon-starved bacteria to protist grazing

Many heterotrophic bacteria possess adaptations for prolonged survival under carbon and energy limitation, generally involving a reduction in cell size and an increased resistance to environmental stress factors. In order to reveal whether carbonstarved bacteria also become less vulnerable to protist grazing, we compared the growth of a bac-terivorous nanoflagellate, Cafeteria roenbergensis, on different physiological states of 3 bacterial strains with well-studied starvation responses (Vibrio vulnificus, Photobacterium angustum and Sphingopyxis alaskensis). Protists achieved high growth rates on all 3 bacterial strains when they were provided in a non-starved state. However, for carbon-starved bacteria, pronounced differences in the response of the flagellates were observed. P. angustum provided similar protist growth for an equal biomass of nonstarved and starved cultures, indicating no change in food quality or grazing resistance for carbon-starved cells, despite smaller cell size. In contrast, starved V. vulnificus did not support protist growth, even resulting in a strong decrease in flagellate numbers at most concentrations tested; and starved S. alaskensis provided only reduced growth rates. Our results demonstrate that (1) feeding on bacteria of smaller cell size does not necessarily impose energy constraints on a flagellate grazer, and (2) a pronounced species-specific variability exists in the susceptibility of carbon-starved bacteria to protist grazing. © 2011 Inter-Research