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 environmental stress factors. In order to reveal whether carbonstarved bacteria also become less vulnerable to protist grazing, we compared the growth of a bacterivorous 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 re sponse 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. KEY WORDS:Grazing vulnerability · Carbon starvation · Growth rate · Protist · Bacteria

Quantitative Infection Dynamics of Cafeteria Roenbergensis Virus

“…Note, our errors here and throughout the rest of the paper refer to standard deviations after accounting for propagation of uncertainty [ 23 ]. The estimated host doubling time is h, which is consistent with the previous reported range of 3.3–8.3 h [ 24 ].…”

The mixotrophic protist Ochromonas danica is an indiscriminant predator whose fitness is influenced by prey type

“…The major predators of bacteria in aquatic systems are heterotrophic and mixotrophic nanoflagellates. Since the recognition of this important predator-prey interaction, many aquatic nutrient dynamics studies have focused on understanding factors that affect predation on bacteria, with particular attention given to the process of prey identi -fication and selection (Pernthaler 2005, Anderson et al 2011.…”

“…However, contrary to expectations, the non-growing bacteria were selectively cropped, while the rapidly growing bacteria were not significantly diminished. Anderson et al (2011) recently suggested that protists may have different responses to growth state of their prey and that these responses may depend on prey species.…”

Some Mixotrophic Flagellate Species Selectively Graze on Archaea

“…Indeed, if small size (i.e., Ͻ0.5 m) constitutes a refuge against grazing, Actinobacteria may be negatively selected only in appearance, either because the limiting size might be an evolved defense mechanism (and thus cells tend to be smaller than those in other groups) or, on the contrary, because preference by grazers is so high that the group is permanently confined to the small-size refuge. It has been suggested that cell miniaturization alone is not sufficient to explain grazing avoidance (48) and that other resistance mechanisms, such as wall structures present in Gram-positive Actinobacteria, are involved in determining a limited edibility (49). Research on prokaryotic grazing is still in its infancy, but our results indicate that random grazing cannot be the paradigm.…”