Adaptation of Bacillus subtilis tat and S313 mutant cells to growth in Lysogeny Broth (LB) lacking NaCl

In B. subtilis, the Tat secretion system is essential for effective growth in media lacking iron or NaCl, which is related to the Tat-dependent export of the heme peroxidase EfeB. In Lysogeny Broth (LB) without NaCl, tat mutant bacteria undergo cell lysis in the early exponential growth phase. Part of the population of mutant bacteria then adapts to the salt-deprived condition and resumes growth. The absence of sRNA S313, which has a predicted role in modulating the expression of the efeUOB operon, also leads to a lysis-recovery phenotype. In this study, the transcriptomes of B. subtilis wild type, tat mutant and S313 mutant were analyzed during lysis and recovery phase in order to elucidate the reasons for lysis of mutant bacteria in the absence of NaCl and subsequent adaptation to this condition. It was, e.g., shown that tat mutant cells suffer from severe oxidative stress and starvation. B. subtilis 168 wild-type, Δtat and ΔS313 mutants were grown aerobically at 37 °C in Lysogeny Broth (1 % tryptone, 0.5 % yeast extract, without NaCl). Samples were taken at two time points. The first was when the lysis of the Δtat mutant started (OD at 600 nm of ~0.9) and the second was the recovery phase (OD at 600 nm of 2). Microarray hybridizations were performed with RNA from three biological replicates. The samples were labeled with Cy3.