METABOLIC ROLES OF A RHODOBACTER-SPHAEROIDES MEMBER OF THE SIGMA(32) FAMILY

We report the role of a gene (rpoH) from the facultative phototroph Rh odobacter sphaeroides that encodes a protein (sigma(37)) similar to Es cherichia coli sigma(32) and other members of the heat shock family of eubacterial sigma factors, X. sphaeroides sigma(37) controls genes th at function during environmental stress, since an R. sphaeroides Delta RpoH mutant is similar to 30-fold more sensitive to the toxic oxyanio n tellurite than wild-type cells, However, the Delta RpoH mutant lacks several phenotypes characteristic of E. coli cells lacking sigma(32). For example, an R. sphaeroides Delta RpoH mutant is not generally def ective in phage morphogenesis, since it plates the lytic virus RSI, as well as its wild-type parent. In characterizing the response of R. sp haeroides to heat, we found that its growth temperature profile is dif ferent when cells generate energy by aerobic respiration, anaerobic re spiration, off photosynthesis. However, growth of the Delta RpoH mutan t is comparable to that of a wild-type strain under each of these cond itions. The Delta RpoH mutant mounted a heat shock response when aerob ically grown cells were shifted from 30 to 42 Alpha degrees C, but it exhibited altered induction kinetics of similar to 120-, 85-, 75-, and 65-kDa proteins, There was also reduced accumulation of several presu med heat shock transcripts (rpoD P-HS, groESL(1), etc,) when aerobical ly grown Delta RpoH cells were placed at 42 degrees C. Under aerobic c onditions, it appears that another sigma factor enables the Delta RpoH mutant to mount a heat shock response, since either RNA polymerase pr eparations from an Delta RpoH mutant, reconstituted E sigma(37), or a holoenzyme containing a 38-kDa protein (sigma(38)) each transcribed E. coli E sigma(38)-dependent promoters. The lower growth temperature pr ofile of photosynthetic cells is correlated with a difference in heat- inducible gene expression, since neither wild-type tells or the Delta RpoH mutant mount a typical heat shock response after such cultures we re shifted from 30 to 37 degrees C.