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

Abstract

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 environmen- tal stress factors. In order to reveal whether carbon- starved 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 vulnifi- cus, 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 bac- teria, pronounced differences in the re sponse of the flagellates were observed. P. angustum provided sim- ilar protist growth for an equal biomass of non- starved 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 result- ing 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 con- straints on a flagellate grazer, and (2) a pronounced species-specific variability exists in the susceptibility of carbon-starved bacteria to protist grazing.