The ancestral Bacillus subtilis strain 3610 contains an 84-kb plasmid called pBS32 that was lost during domestication of commonly used laboratory derivatives. Here we demonstrate that pBS32, normally present at 1 or 2 copies per cell, increases in copy number nearly 100-fold when cells are treated with the DNA-damaging agent mitomycin C. Mitomycin C treatment also caused cell lysis dependent on pBS32-borne prophage genes. ZpdN, a sigma factor homolog encoded by pBS32, was required for the plasmid response to DNA damage, and artificial expression of ZpdN was sufficient to induce pBS32 hyperreplication and cell death. Plasmid DNA released by cell death was protected by the capsid protein ZpbH, suggesting that the plasmid was packaged into a phagelike particle. The putative particles were further indicated by CsCl sedimentation but were not observed by electron microscopy and were incapable of killing B. subtilis cells extracellularly. We hypothesize that pBS32-mediated cell death releases a phagelike particle that is defective and unstable. IMPORTANCEProphages are phage genomes stably integrated into the host bacterium's chromosome and less frequently are maintained as extrachromosomal plasmids. Here we report that the extrachromosomal plasmid pBS32 of Bacillus subtilis encodes a prophage that, when activated, kills the host. pBS32 also encodes both the sigma factor homolog ZpdN that is necessary and sufficient for prophage induction and the protein ComI, which is a potent inhibitor of DNA uptake by natural transformation. We provide evidence that the entire pBS32 sequence may be part of the prophage and thus that competence inhibition may be linked to lysogeny.

Actinomycetes are a gram-positive, filamentous subgroup of bacteria most known for antibiotic production. In fact, most of the antibiotics available today have originated from actinomycetes, namely from the genus Streptomyces. Novel bacteria with antimicrobial activities have been discovered from bacterial screen studies for decades and there is still much more yet to be unearthed. One hundred seventy five strains of actinomycetes were isolated from 38 different soil samples from different locations in Patna, India. Potential antibiotic producers were screened against four test microorganisms (Escherichia coli MTCC 739, Staphylococcus aureus MTCC 96, Streptomyces lividans TK23 MTCC 4 and Candida albicans MTCC 227). The bioassay revealed that about 26% of actinomycetes isolates were active against at least one of the test microorganism. Characterization of a selected isolate has led to identification of a unique strain of actinomycetes (MP 525) showing broad-spectrum antibacterial and antifungal properties. The strain MP 525 has been morphologically characterized as Streptomyces sp. and deposited at MTCC, Chandigarh, India with accession number 8723. The 16S rRNA gene of the strain Streptomyces sp. US7 MTCC 8723 was sequenced and the DNA sequence was deposited at NCBI, Bethesda (GenBank accession. No. HQ659005). On the basis of λmax values of culture filtrates, it has been suggested that the strain might be producing LL-E19085-like antibacterial and a flavone glycoside-like antifungal antibiotics, which can be further exploited for industrial and biological applications.

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Rhodobacter sphaeroides 2.4.1 belongs to theα-3 subdivision of the Proteobacteria. It possesses a multipartite genome structure consisting of two circular chromosomes, andit displays a wide range of metabolic diversity.Approximately 40 flagellar proteins are required for structure, assembly, and regulation of the flagellum formation in most bacterial species. R. sphaeroidescontains two flagellar gene clusters (fla1 and fla2),which encode 38 and 21 proteins, respectively. Thirty-six of these genes exist in duplicate gene-pairs.A combination of genome analysis, phylogenetic analysis and mRNA expression analysis were employed to examine the conservation of structure, function and evolution of fla1 and fla2 in R. sphaeroides. The results demonstrated that fla2, which was shared among members of α-Proteobacteria, is native toR. sphaeroides, while fla1 was horizontally transferred from a member of γ-Proteobacteria.In addition, genes located in fla1 are expressed over several growth conditions, but those in fla2 are barely expressed.