Rapid adaptation of predation resistance in bacteria isolated from a seawater microcosm

Abstract

Bacterial defense against protozoan grazing has been shown to occur in many different bacteria. Predation resistance traits may however be plastic, making bacterial com munities resilient or resistant to predation perturbations. We studied the adaptation of pre dation resistance traits in bacteria isolated from a microcosm experiment. In the initial microcosm ex periment the predation pressure on bacteria varied markedly, while changes in the bacterial community composition could not be verified. Seven bacteria were isolated from the microcosm (Micrococcus sp., Rhodobacter sp., Paracoccus sp., Shewanella sp., Rhizobium sp. and 2 un identified species) and these were repeatedly exposed to high predation by the ciliate Tetrahymena pyriformis. High variations in edibility and rate of adaptation of predation resistance traits were observed among the strains. The initial mortality rate of the different bacterial taxa and the change over time varied by a factor of 7 and 24, respectively. Rhodobacter sp. was already predation resistant at the start of the experiment and did not change much over time, while Micrococcus sp., Paracoccus sp. and Shewanella sp. initially were relatively edible and later developed predation resistance. In conclusion, we show that rapid adaptation of predation resistance traits is common among bacteria in an aquatic microbial community, and that a single test of a bacterium's edibility will in many cases not be enough to fully understand its ecological role, as it will not reveal the potential adaptive response. The results suggest the potential of rapid changes of predation resistance as a mechanism for bacterial communities to be resilient to variations in predation disturbances.