Role of sigma(B) in heat, ethanol, acid, and oxidative stress resistance and during carbon starvation in Listeria monocytogenes

To determine the contribution of sigma B (sigma (B)) to survival of station ary-phase Listeria monocytogenes cells following exposure to environmental stresses, we compared the viability of strain 10403S with that of an isogen ic nonpolar sigB null mutant strain after exposure to heat (50 degreesC), e thanol (16.5%), or acid (pH 2.5). Strain viabilities were also determined u nder the same conditions in cultures that had been previously exposed to su blethal levels of the same stresses (45 degreesC, 5% ethanol, or pH 4.5). T he Delta sigR and wild-type strains had similar viabilities following expos ure to ethanol and heat, but the Delta sigB strain was almost 10,000-fold s nore susceptible to lethal acid stress than its parent strain. However, a 1 -h preexposure to pH 4.5 yielded a 1,000-fold improvement in viability for the Delta sigB strain. These results suggest the existence in L. monocytoge ns of both a ors-dependent mechanism and a pH-dependent mechanism for acid resistance in the stationary phase. as contributed to resistance to both ox idative stress and carbon starvation in L. monocytogenes. The Delta sigB st rain was 100-fold more sensitive to 13.8 mM cumene hydroperoxide than the w ild-type strain. Following glucose depletion, the Delta sigB strain lost vi ability more rapidly than the parent strain. sigma (B) contributions to via bility during carbon starvation and to acid resistance and oxidative stress resistance support the hypothesis that ors plays a role in protecting L. m onocytogenes against environmental adversities.