The thermosensitive phenotype of an Escherichia coli sbmA tolC double mutant results from a higher sensitivity to exogenous hydrogen peroxide

SALOMÓN, RA; ARIAS, VJ; LACHENICHT, JA; VALLEJOS, AC

Ciudad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedades de Biociencias

Microorganisms live in environments where they are sometimes exposed to different types of stress (high temperatures, oxidative damage, etc) which can be lethal. Therefore bacteria have evolved diverse mechanisms to overcome these adverse conditions. We have previously reported that an Escherichia coli sbmA tolC double mutant is unable to form colonies at 42°C in LB plates. The molecular bases of this phenotype remain unknown. In the present study we demonstrate that the growth defect may be corrected by the addition of either iron, enterobactin or its degradation products to the medium, suggesting that iron starvation is the cause of the phenotype. To test this possibility, we used a reporter plasmid carrying a transcriptional fusion between lacZ and the ryhB promoter, which is induced under iron deficiency. Results showed that the double mutant was not under iron starvation and it was capable of incorporating iron. We also found that the addition of exogenous catalase to the medium suppressed the thermosensitive phenotype. There is evidence indicating that hydrogen peroxide is generated abiotically in LB medium via autoxidation. Moreover, relieving of the phenotype by iron could be due to direct scavenging of hydrogen peroxide by the metal. Taken together, our results indicate that the thermosensitive phenotype of the double mutant sbmA tolC may result from an increased sensitivity to hydrogen peroxide when the cells grow at low densities.