Genetic and physiological studies of an Escherichia coli sbmA tolC double mutant

ARIAS, V. J.; LACHENICHT, J. A.; VALLEJOS, A. C.; SALOMÓN, R. A.

Mar del Plata

Congreso; 51 Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2015

SAIB

We have previously shown that the combined loss of the inner membrane protein SbmA and the outer membrane protein TolC in Escherichia coli K-12 results in an inability to form colonies at 42°C in LB medium. Each mutation alone does not exhibit heat sensitivity. To test whether this phenotype is strain-dependent, in the present study we introduced both mutations in another background and found that the newly constructed mutant displays the same phenotype. Interestingly, we found that E. coli K-12 strains produce a diffusible factor that restores the ability of the sbmA tolC mutant to form colonies at 42°C. This factor is secreted both in solid and liquid culture media. E. coli K-12 strains with mutations blocking the synthesis of the siderophore enterobactin (aroB and entE) do not produce the stimulating factor, suggesting that it could be enterobactin. Mutants in entS and tolC (in which enterobactin excretion is highly reduced) are also capable of promoting the growth of the double mutant at 42°C. This could be explained by assuming that the degradation products of enterobactin, whose excretion is not affected in entS and tolC mutant strains, also have factor activity. Our results suggested that the thermosensitive phenotype of the double mutant sbmA tolC may result from iron limitation. This is supported by the observation that addition of exogenous iron relieves the phenotype.