Two Bacillus subtilis genes, designated resD and resE, encode proteins that are similar to those of twocomponent signal transduction systems and play a regulatory role in respiration. The overlapping resD-resE genes are transcribed during vegetative growth from a very weak promoter directly upstream of resD. They are also part of a larger operon that includes three upstream genes, resABC (formerly orfX14, -15, and -16), the expression of which is strongly induced postexponentially. ResD is required for the expression of the following genes: resA, ctaA (required for heme A synthesis), and the petCBD operon (encoding subunits of the cytochrome bf complex). The resABC genes are essential genes which encode products with similarity to cytochrome c biogenesis proteins. resD null mutations are more deleterious to the cell than those of resE. resD mutant phenotypes, directly related to respiratory function, include streptomycin resistance, lack of production of aa 3 or caa 3 terminal oxidases, acid accumulation when grown with glucose as a carbon source, and loss of ability to grow anaerobically on a medium containing nitrate. A resD mutation also affected sporulation, carbon source utilization, and Pho regulon regulation. The data presented here support an activation role for ResD, and to a lesser extent ResE, in global regulation of aerobic and anaerobic respiration in B. subtilis.

BaciUlus subtilis has an alkaline phosphatase (APase) gene

SummaryThe Bacillus subtilis ResD-ResE two-component system is responsible for the regulation of a number of genes involved in cytochrome c biogenesis and haem A biosynthesis, and it is required for anaerobic respiration in this organism. We reported previously that the operon encoding these regulatory proteins, the resABCDE operon, is induced under several conditions, one of which is phosphate starvation. We report here that this transcription requires the PhoP-PhoR two-component system, whereas other induction conditions do not. The PhoPϳP response regulator directly binds to and is essential for transcriptional activation of the resABCDE operon as well as being involved in repression of the internal resDE promoter during phosphate-limited growth. The concentration of ResD in various phoP mutant strains corroborates the role of PhoP in the production of ResD. These interactions result in a regulatory network that ties together the cellular functions of respiration/energy production and phosphate starvation. Significantly, this represents the first evidence for direct involvement of one two-component system in transcription of a second two-component system.

Alkaline phosphatase (APase) is induced as a culture enters stationary phase because of limiting phosphate.The results presented here show that expression of APase is regulated both negatively and positively. PhoP, a homolog of a family of bacterial transcription factors, and PhoR, a homolog of bacterial histidine protein kinases, are required for induction of APases when phosphate becomes limiting. The induction period lasts 2 to 3 h, after which the rate of APase accumulation is decreased. Mutant strains defective in the SpoOA transcription factor failed to decrease APase production. The consequent hyperinduction of APase in a spoOA strain was dependent on phoP and phoR. spoOB and spoOF strains also overexpressed APase, suggesting that phosphorylated SpoiA is required for repression of APase. An abrB mutant allele in the presence of the mutant spoOA allele in these strains did not significantly change the APase hyperinduction phenotype, demonstrating that SpoOA repression ofabrB expression is not the mechanism by which SpoOA-P regulates APase expression. Our previous report that spoOA mutants do not express APases is in conflict with the present data. We show here that the previously used mutants and a number of commonly used spo0 strains, all of which have an APase deficiency phenotype, contain a previously unrecognized mutation in phoR.

Monosporascus cannonballus is a soilborne fungal pathogen that causes vine-decline of muskmelon which results in reduced yield in many melon growing areas around the world. M. cannonballus isolates were collected from different provinces in Spain and experiments conducted to determine pigmentation, perithecial formation, and the presence of cellular dsRNA. Thirty-one isolates were grouped based on dsRNA fragment sizes using cluster analysis and Euclidean distances. Three distinct dsRNA groupings were observed. Group 2 isolates containing 2, 3, and 3.5 kb dsRNA appeared to exhibit a decrease in perithecia production compared to the other groups. Group 1 isolates exhibited yellow pigmentation only, while Group 3 isolates expressed grey (wild-type) and yellow (degenerate) pigmentation. Isolates that did not contain dsRNA (Group 4) exhibited wild-type pigmentation. Down-regulation and variation in phenotype are hypothesized to be due to dsRNA/iRNA interactions with the fungal transcription mechanisms. Future research will focus on elucidating the mechanisms of regulation by the dsRNA of M. cannonballus.