Altered stationary-phase response in a Borrelia burgdorferi ropS mutant

The homolog of the chromosomally encoded stationary-phase sigma factor RpoS in Borrelia burgdorferi was inactivated using gyrB(r) as a selectable mark er. Two-dimensional nonequilibrium pH gradient electrophoresis of stationar y-phase cell lysates identified at least 11 differences between the protein profiles of the rpoS mutant and wild-type organisms. Wild-type B. burgdorf eri had a growth phase-dependent resistance to 1 N NaCl, similar to the sta tionary-phase response reported for other bacteria. The B. burgdorferi rpoS mutant strain was less resistant to osmotic stress in stationary phase tha n the isogenic rpoS wild-type organism. The results indicate that the B. bu rgdorferi rpoS homolog influences protein composition and participates in s tationary-phase-dependent osmotic resistance. This rpoS mutant will be usef ul for studying regulation of gene expression in response to changing envir onmental conditions.