GROWTH, PIGMENTATION, AND EXPRESSION OF THE PUF AND PUC OPERONS IN A LIGHT-RESPONDING-REPRESSOR (SPB)-DISRUPTED RHODOBACTER-SPHAEROIDES

We previously cloned a trans-repressor, SPB, for the puf operon of Rho dobacter sphaeroides (Shimada et al. 1996) and revealed that SPB was a putative genetic counterpart to HvrA in Rhodobacter capsulatus, a tra ns-activator for the puf and puh operons (Mizoguchi et al, 1997), In t his study we constructed a spb-disrupted R. sphaeroides, strain L-7, t o elucidate the function of SPB, This disruption of the spb gene incre ased the photosynthetic growth rate and the cellular levels of photopi gments under low-intensity light conditions, The disruption also derep ressed the expression of the puf and puc operons under high-intensity light conditions. In strain L-7, however, strong illumination still re duced the cellular levels of photopigments as it did in the wild strai n, suggesting that SPB did not directly affect the formation of photop igments, These results support our previous suggestion that SPB functi ons as a high-light repressor for puf operon in R. sphaeroides in stri king contrast to HvrA, which is a low-light activator for puf and puh operons in R. capsulatus, even though SPB and HvrA are highly homologo us, Disruption of spb gene had no effect on the oxygen-mediated regula tion of the pigmentation or the expression of puf and puc operons.