Resistance to environmental stress by the mucoid and the non-mucoid variant phenotypes of the Comamonas testosteroni strain A20

The Comamonas testosteroni strain A20, isolated from activated sludge, displays a phase variation between a mucoid (exopolysaccharide producing) and a non-mucoid colony phenotype. It was found that a population of C. testosteroni cells, subjected to sublethal environmental stress (acute heat shock and reactive oxidative intermediates and visible light), became selectively enriched in non-mucoid colony forming cells (NMCF cells). This observation suggests that NMCF cells are more stress-resistant than MCF cells. The experiments did not allow us to establish whether stress acts as a trigger for phase conversion or as a selector for the more stress-resistant NMCF cells. NMCF cells are more hydrophobic than MCF cells as evidenced by a better attachment to gas bubbles and polystyrene. These observations suggest that the two phenotypic variants might have different ecophysiological functions.