Direct and Indirect Effects of Protist Predation on Population Size Structure of a Bacterial Strain with High Phenotypic Plasticity

Open Access
Publisher Website
Google Scholar
Abstract
We studied the impact of grazing and substrate supply on the size structure of a freshwater bacterial strain (Flectobacillussp.) which showed pronounced morphological plasticity. The cell length varied from 2 to >40 μm and encompassed rods, curved cells, and long filaments. Without grazers and with a sufficient substrate supply, bacteria grew mainly in the form of medium-sized rods (4 to 7 μm), with a smaller proportion (Ochromonassp. showed that freely suspended cells of 80% filamentous cells. These attained a biomass comparable to that of populations in chemostats without grazers, which were composed of medium-sized rods and c-shaped cells. Carbon starvation resulted in a fast decrease in cell length and a shift towards small rods, which were highly vulnerable to grazing. Dialysis bag experiments in combination with continuous cultivation revealed that filament formation was significantly enhanced even without direct contact of bacteria with bacterivores and was thus probably stimulated by grazer excretory products.