Regulatory interactions between the Pho and {sigma}B-dependent general stress regulons of Bacillus subtilis

Department of Microbiology and Immunology, The Medical School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4HH, UK 1 Author for correspondence: Colin R. Harwood. Tel: +44 191 222 7708. Fax: +44 191 222 7736. e-mail: Colin.Harwood{at}ncl.ac.uk When Bacillus subtilis is subjected to phosphate starvation, the Pho and B -dependent general stress regulons are activated to elicit, respectively, specific and non-specific responses to this nutrient-limitation stress. A set of isogenic mutants, with a ß-galactosidase reporter gene transcriptionally fused to the inactivated target gene, was used to identify genes of unknown function that are induced or repressed under phosphate limitation. Nine phosphate-starvation-induced ( psi ) genes were identified: yhaX , yhbH , ykoL and yttP were regulated by the PhoP–PhoR two-component system responsible for controlling the expression of genes in the Pho regulon, while ywmG (renamed csbD ), yheK , ykzA , ysnF and yvgO were dependent on the alternative sigma factor B , which controls the expression of the general stress genes. Genes yhaX and yhbH are unique members of the Pho regulon, since they are phosphate-starvation induced via PhoP–PhoR from a sporulation-specific E promoter or a promoter that requires the product of a E -dependent gene. Null mutations in key regulatory genes phoR and sigB showed that the Pho and B -dependent general stress regulons of Bacillus subtilis interact to modulate the levels at which each are activated. Keywords: stress response, psi genes, phosphate starvation, regulatory networks Abbreviations: APase, alkaline phosphatase; BFA, Bacillus subtilis functional analysis; HPM, high-phosphate medium; LPM, low-phosphate medium; B -GS, B -dependent general stress