Summary: The master regulator for entry into sporulation in Bacillus subtilis is the DNA‐binding protein Spo0A, which has been found to influence, directly or indirectly, the expression of over 500 genes during the early stages of development. To search on a genome‐wide basis for genes under the direct control of Spo0A, we used chromatin immunoprecipitation in combination with gene microarray analysis to identify regions of the chromosome at which an activated form of Spo0A binds in vivo. This information in combination with transcriptional profiling using gene microarrays, gel electrophoretic mobility shift assays, using the DNA‐binding domain of Spo0A, and bioinformatics enabled us to assign 103 genes to the Spo0A regulon in addition to 18 previously known members. Thus, in total, 121 genes, which are organized as 30 single‐gene units and 24 operons, are likely to be under the direct control of Spo0A. Forty of these genes are under the positive control of Spo0A, and 81 are under its negative control. Among newly identified members of the regulon with transcription that was stimulated by Spo0A are genes for metabolic enzymes and genes for efflux pumps. Among members with transcription that was in‐hibited by Spo0A are genes encoding components of the DNA replication machinery and genes that govern flagellum biosynthesis and chemotaxis. Also in‐cluded in the regulon are many (25) genes with products that are direct or indirect regulators of gene transcription. Spo0A is a master regulator for sporulation, but many of its effects on the global pattern of gene transcription are likely to be mediated indirectly by regulatory genes under its control.

Staphylococcus aureus is a clinically important pathogen that causes a wide range of human infections, from minor skin infections to severe tissue infection and sepsis. S. aureus has a high level of antibiotic resistance and is a common cause of infections in hospitals and the community. The rising prevalence of community-acquired methicillin-resistant S. aureus (CA-MRSA), combined with the important severity of S. aureus infections in general, has resulted in the frequent use of anti-staphylococcal antibiotics, leading to increasing resistance rates. Antibiotic-resistant S. aureus continues to be a major health concern, necessitating the development of novel therapeutic strategies. S. aureus uses a wide range of virulence factors, such as toxins, to develop an infection in the host. Recently, anti-virulence treatments that directly or indirectly neutralize S. aureus toxins have showed promise. In this review, we provide an update on toxin pathogenic characteristics, as well as anti-toxin therapeutical strategies.

Additional targets of CodY, a GTP-activated repressor of early stationary-phase genes inBacillus subtilis, were identified by combining chromatin immunoprecipitation, DNA microarray hybridization, and gel mobility shift assays. The direct targets of CodY newly identified by this approach included regulatory genes for sporulation, genes that are likely to encode transporters for amino acids and sugars, and the genes for biosynthesis of branched-chain amino acids.

In the Gram‐positive, antibiotic‐producing bacterium Streptomyces coelicolor A3(2), the thiol‐disulphide status of the hyphae is controlled by a novel regulatory system consisting of a sigma factor, σ^R, and its cognate anti‐sigma factor, RsrA. Oxidative stress induces intramolecular disulphide bond formation in RsrA, which causes it to lose affinity for σ^R, thereby releasing σ^R to activate transcription of the thioredoxin operon, trxBA. Here, we exploit a preliminary consensus sequence for σ^R target promoters to identify 27 new σ^R target genes and operons, thereby defining the global response to disulphide stress in this organism. Target genes related to thiol metabolism encode a second thioredoxin (TrxC), a glutaredoxin‐like protein and enzymes involved in the biosynthesis of the low‐molecular‐weight thiol‐containing compounds cysteine and molybdopterin. In addition, the level of the major actinomycete thiol buffer, mycothiol, was fourfold lower in a sigR null mutant, although no candidate mycothiol biosynthetic genes were identified among the σ^R targets. Three σ^R target genes encode ribosome‐associated products (ribosomal subunit L31, ppGpp synthetase and tmRNA), suggesting that the translational machinery is modified by disulphide stress. The product of another σ^R target gene was found to be a novel RNA polymerase‐associated protein, RbpA, suggesting that the transcriptional machinery may also be modified in response to disulphide stress. We present DNA sequence evidence that many of the targets identified in S. coelicolor are also under the control of the σ^R homologue in the actinomycete pathogen Mycobacterium tuberculosis.

Summary: A complex programme of regulation governs gene expression during development of the morphologically and biochemically complex eubacterial genus Streptomyces. Earlier work has suggested a model in which ‘higher level’ pleiotropic regulators activate ‘pathway‐specific’ regulators located within chromosomal gene clusters encoding biosynthesis of individual antibiotics. We used mutational analysis and adventitious overexpression of key Streptomyces coelicolor regulators to investigate functional interactions among them. We report here that cluster‐situated regulators (CSRs) thought to be pathway‐specific can also control other antibiotic biosynthetic gene clusters, and thus have pleiotropic actions. Surprisingly, we also find that CSRs exhibit growth‐phase‐dependent control over afsR2/afsS, a ‘higher level’ pleiotropic regulatory locus not located within any of the chromosomal gene clusters it targets, and further demonstrate that cross‐regulation by CSRs is modulated globally and differentially during the S. coelicolor growth cycle by the RNaseIII homologue AbsB. Our results, which reveal a network of functional interactions among regulators that govern production of antibiotics and other secondary metabolites in S. coelicolor, suggest that revision of the currently prevalent view of higher‐level versus pathway‐specific regulation of secondary metabolism in Streptomyces species is warranted.