[Ecological-genetic mechanisms of the transition of Salmonella typhimurium to the dormant state in the environment]

The dynamics of vegetative and dormant (noncultivable) of S. typhimurium cells of two isogenic strains in association with microalgae Scenedesmus quadricauda and under the action of the exometabolites of the algae at different stages of their growth was studied using in parallel bacteriological method and PCR. The study revealed that at the stage of active growth green algae and their metabolic products maintain the survival of salmonellae (strain TR = 1) vegetative forms in water at an optimum temperature. Low temperatures induced their gradual (3 weeks) transition to the dormant state. The exometabolites of old dying algae induced the rapid (several hours) and complete transition of the bacterial population (TR = 1) to noncultivable state. In our experiments the insertional mutation in gene pqi (strain PhoA = 8), inducing the defect of transmembrane protein and disturbances in the transition of salmonellae to dormant state, led to stable existence (lasting 7 months, i.e. the whole term of observation) of vegetative cells. The natural inducers tried in our experiments did not lead to the formation of the dormant forms of salmonellae in this mutant strain.