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PspG, a New Member of the Yersinia enterocolitica Phage Shock Protein Regulon. Rebecca C. Green, 2004.The Yersinia enterocolitica phage shock protein (Psp) system is induced when the Ysc type III secretion system is produced or when only the YscC secretin component is synthesized . Some psp null mutants have a growth defect when YscC is produced and a severe virulence defect in animals . The Y . enterocolitica psp locus is made up of two divergently transcribed cistrons, pspF and pspABCDycjXF . pspA operon expression is dependent on RpoN (  54)
and the enhancer-binding protein PspF . Previous data indicated that
PspF also controls at least one gene that is not part of the psp
locus . In this study we describe the identification of pspG, a
new member of the PspF regulon . Predicted RpoN-binding sites upstream
of the pspA genes from different bacteria have a common
divergence from the consensus sequence, which may be a signature of
PspF-dependent promoters . The Y . enterocolitica pspG gene was
identified because its promoter also has this signature . Like the
pspA operon, pspG is positively regulated by PspF,
negatively regulated by PspA, and induced in response to the
production of secretins . Purified His6-PspF protein specifically
interacts with the pspA and pspG control regions . A pspA
operon deletion mutant has a growth defect when the YscC secretin is
produced and a virulence defect in a mouse model of infection .
These phenotypes were exacerbated by a pspG null mutation . Therefore,
PspG is the missing component of the Y . enterocolitica Psp regulon
that was previously predicted to exist .
ATP-Binding Cassette Transport System Involved in Regulation of Morphological Differentiation in Response to Glucose in Streptomyces griseus. Jeong-Woo Seo, 2002.Streptomyces griseus NP4, which was derived by UV mutagenesis from strain IFO13350, showed a bald and wrinkled colony morphology in response to glucose . Mutant NP4 formed ectopic septa at intervals along substrate hyphae, and each of the compartments developed into a spore which was indistinguishable from an aerial spore in size, shape, and thickness of the spore wall and in susceptibility to lysozyme and heat . The ectopic spores of NP4 formed in liquid medium differed from "submerged spores" in lysozyme sensitivity . Shotgun cloning experiments with a library of the chromosomal DNA of the parental strain and mutant NP4 as the host gave rise to DNA fragments giving two different phenotypes; one complementing the bald phenotype of the host, and the other causing much severe wrinkled morphology in the host . Subcloning identified a gene (dasR) encoding a transcriptional repressor belonging to the GntR family that was responsible for the reversal of the bald phenotype and a gene (dasA) encoding a lipoprotein probably serving as a substrate-binding protein in an ATP-binding cassette (ABC) transport system that was responsible for the severe wrinkled morphology . These genes were adjacent but divergently encoded . Two genes, named dasB and dasC, encoding a membrane-spanning protein were present downstream of dasA, which suggested that dasRABC comprises a gene cluster for an ABC transporter, probably for sugar import . dasR was transcribed actively during vegetative growth, and dasA was transcribed just after commencement of aerial hypha formation and during sporulation, indicating that both were developmentally regulated . Transcriptional analysis and direct sequencing of dasRA in mutant NP4 suggested a defect of this mutant in the regulatory system to control the expression of these genes . Introduction of multicopies of dasA into the wild-type strain caused ectopic septation in very young substrate hyphae after only 1 day of growth and subsequent sporulation in response to glucose . The ectopic spores of the wild type had a thinner wall than those of mutant NP4, in agreement with the observation that the former was sensitive to lysozyme and heat . Disruption of the chromosomal dasA or dasR in the wild-type strain resulted in growth as substrate mycelium, suggesting an additional role of these genes in aerial mycelium formation . The ectopic septation and sporulation in mutant NP4 and the wild-type strain carrying multicopies of dasA were independent of a microbial hormone, A-factor (2-isocapryloyl-3R-hydroxymethyl-  -butyrolactone), that acts as a master switch of aerial mycelium formation and secondary metabolism .
For the Insect Pathogen Photorhabdus luminescens, Which End of a Nematode Is Out?. Todd A. Ciche, 2003.The nematode Heterorhabditis bacteriophora is the vector for transmitting the entomopathogenic bacterium Photorhabdus luminescens between insect larvae . The dauer juvenile (DJ) stage nematode selectively retains P . luminescens in its intestine until it releases the bacteria into the hemocoel of an insect host . We report the results of studying the transmission of the bacteria by its nematode vector . Cells of P . luminescens labeled with green fluorescent protein preferentially colonized a region of the DJ intestine immediately behind the basal bulb, extending for various distances toward the anus . Incubation of DJ nematodes in vitro in insect hemolymph induced regurgitation of the bacteria . Following a 30-min lag, the bacteria migrated in a gradual and staggered movement toward and ultimately exited the mouth . This regurgitation reaction was induced by a low-molecular-weight, heat- and protease-stable, anionic component present in arthropod hemolymph and in supernatants from insect cell cultures . Nematodes anesthetized with levamisole or treated with the antihelmenthic agent ivermectin did not release their bacteria into hemolymph . The ability to visualize P . luminescens in the DJ nematode intestine provides the first clues to the mechanism of release of the bacteria during infection of insect larvae . This and the partial characterization of a component of hemolymph triggering release of the bacteria render this fascinating example of both a mutualistic symbiosis and disease transmission amenable to future genetic and molecular study .
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