ESCHERICHIA COLI MUTATIONS AFFECTING VIABILITY IN STATIONARY PHASE

DE CRISTÓBAL, RICARDO E.; VINCENT, PAULA A.; SALOMÓN, RAÚL A.

Mar del Plata

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular.; 2007

Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular.

Escherichia coli cultures show a biphasic death curve after entry into stationary phase, with viable counts dropping by one log unit in the first four days of incubation. Afterwards the remaining viable cells die much more slowly. The triggers for the transition from stationary phase to death phase and even the mechanism(s) of cell death are not well understood. We have found that for an E. coli sbmA mutant the death phase is dramatically exacerbated. In fact, after 4 days in stationary phase there is a loss of viability of at least three log units. To test whether the reduction in colony forming units (CFU) in the plating assays was due to a loss of viability and not simply to a viable but non culturable state, we employed the Live Dead Bac Light fluorescence-based assay. The results indicated that the reduction in colony counts indeed reflected death of the cels. When the sbmA mutation was complemented by a plasmid harboring the sbmA gene, the phenotype was not reversed. This suggested that there is probably another mutation in the strain used, MC4100, that, when combined with sbmA, led to the increased loss of viability. We are currently testing this hypothesis. This is the first time that a physiological phenotype is described for a sbmA mutant. Our results could throw light on the factor(s) that mark the transition between stationary and death phases.