Transcriptional and preliminary functional analysis of the six genes located in divergence of phoR/phoP in Streptomyces lividans

Streptomyces lividans senses and adjusts to a situation of Pi limitation via the expression of genes of the pho regulon controlled by the two-component system PhoR/PhoP. Interestingly, an in silico analysis of the proteins encoded by the six genes located in divergence of phoR/phoP revealed that the latter bear features often found in metalloproteins involved in the sensing/resistance to oxidative stress. We determined whether genes of this region were belonging to the pho regulon and whether the encoded proteins do play a role in the resistance to oxidative stress. For this purpose, a transcriptional analysis of these genes was carried out on the carbon and nitrogen rich medium R2YE and on a minimal medium (MM). On R2YE, the expression of the genes phoU to sco4225 was much higher than on MM and constant throughout growth. On this medium, the expression of phoU was totally PhoP-dependent whereas the expression of sco4227 and sco4226 was partially PhoP-dependent, taking place from the phoU promoter region. In contrast, on MM, the expression of sco4227 and sco4226 was PhoP-independent whereas that of phoU remained PhoP-dependent and showed, as phoR/phoP, a peak of expression at 48 h. sco4225, sco4224, and sco4223 were transcribed from their own promoter independently of PhoP in both media. The mutants of five out of six genes of the region (Delta sco4226 mutant could not be obtained) grew poorly in the presence of exogenous oxidants, suggesting a role of the encoded proteins in the resistance to oxidative stress, especially on the rich medium R2YE.