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 produc ing) 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 li ght), 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 establi sh whether stress acts as a trigger for phase conversion or as a selec tor for the more stress-resistant NMCF cells. NMCF cells are more hydr ophobic than MCF cells as evidenced by a better attachment to gas bubb les and polystyrene. These observations suggest that the two phenotypi c variants might have different ecophysiological functions.