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Penetration of Membrane-Containing Double-Stranded-DNA Bacteriophage PM2 into Pseudoalteromonas Hosts. Hanna M. Kivelä, 2004.The icosahedral bacteriophage PM2 has a circular double-stranded DNA (dsDNA) genome and an internal lipid membrane . It is the only representative of the Corticoviridae family . How the circular supercoiled genome residing inside the viral membrane is translocated into the gram-negative marine Pseudoalteromonas host has been an intriguing question . Here we demonstrate that after binding of the virus to an abundant cell surface receptor, the protein coat is most probably dissociated . During the infection process, the host cell outer membrane becomes transiently permeable to lipophilic gramicidin D molecules proposing fusion with the viral membrane . One of the components of the internal viral lipid core particle is the integral membrane protein P7, with muralytic activity that apparently aids the process of peptidoglycan penetration . Entry of the virion also causes a limited depolarization of the cytoplasmic membrane . These phenomena differ considerably from those observed in the entry process of bacteriophage PRD1, a dsDNA virus, which uses its internal membrane to make a cell envelope-penetrating tubular structure . Heads or Tails: Host-Parasite Interactions in the Drosophila-Wolbachia System. Zoe Veneti, 2004.Wolbachia strains are endosymbiotic bacteria typically found in the reproductive tracts of arthropods . These bacteria manipulate host reproduction to ensure maternal transmission . They are usually transmitted vertically, so it has been predicted that they have evolved a mechanism to target the host's germ cells during development . Through cytological analysis we found that Wolbachia strains display various affinities for the germ line of Drosophila . Different Wolbachia strains show posterior, anterior, or cortical localization in Drosophila embryos, and this localization is congruent with the classification of the organisms based on the wsp (Wolbachia surface protein) gene sequence . This embryonic distribution pattern is established during early oogenesis and does not change until late stages of embryogenesis . The posterior and anterior localization of Wolbachia resembles that of oskar and bicoid mRNAs, respectively, which define the anterior-posterior axis in the Drosophila oocyte . By comparing the properties of a single Wolbachia strain in different host backgrounds and the properties of different Wolbachia strains in the same host background, we concluded that bacterial factors determine distribution, while bacterial density seems to be limited by the host . Possible implications concerning cytoplasmic incompatibility and evolution of strains are discussed . Bacterial Population Changes in a Membrane Bioreactor for Graywater Treatment Monitored by Denaturing Gradient Gel Electrophoretic Analysis of 16S rRNA Gene Fragments. David M. Stamper, 2003.The bacterial population of a graywater treatment system was monitored over the course of 100 days, along with several wastewater biochemical parameters . The graywater treatment system employed an 1,800-liter membrane bioreactor (MBR) to process the waste, with essentially 100% recycling of the biomass . Graywater feed consisting of 10% galley water and 90% laundry water, selected to approximate the graywater composition on board U.S . Navy ships, was collected offsite . Five-day biological oxygen demand (BOD5), oils and greases (O/G), nitrogen, and phosphorus were monitored in the feed and were found to vary greatly day to day . Changes in the bacterial population were monitored by PCR amplification of region 332 to 518 (Escherichia coli numbering) of the 16S rRNA gene and denaturing gradient gel electrophoresis (DGGE) analysis of the resultant PCR products . DGGE analysis indicated a diverse and unstable bacterial population throughout the 100-day period, with spikes in feed strength causing significant changes in community structure . Long-term similarity between the communities was 0 to 25%, depending on the method of analysis . In spite of the unstable bacterial population, the MBR system was able to meet effluent quality parameters approximately 90% of the time . Plasmid Introduction in Metal-Stressed, Subsurface-Derived Microcosms: Plasmid Fate and Community Response. Barth F. Smets, 2003.The nonconjugal IncQ plasmids pMOL187 and pMOL222, which contain the metal resistance-encoding genes czc and ncc, were introduced by using Escherichia coli as a transitory delivery strain into microcosms containing subsurface-derived parent materials . The microcosms were semicontinuously dosed with an artificial groundwater to set a low-carbon flux and a target metal stress (0, 10, 100, and 1,000 µM CdCl2), permitting long-term community monitoring . The broad-host-range IncP  plasmid RP4 was also transitorily introduced into a subset of microcosms . No novel community phenotype was detected after plasmid delivery, due to the high background resistances to Cd and Ni . At fixed Cd doses, however, small but consistent increases in Cdr or Nir density were measured due to the introduction of a single pMOL plasmid, and this effect was enhanced by the joint introduction of RP4; the effects were most significant at the highest Cd doses . The pMOL plasmids introduced could, however, be monitored via czc- and ncc-targeted infinite-dilution PCR (ID-PCR) methods, because these genes were absent from the indigenous community: long-term presence of czc (after 14 or 27 weeks) was contingent on the joint introduction of RP4, although RP4 cointroduction was not yet required to ensure retention of ncc after 8 weeks . Plasmids isolated from Nir transconjugants further confirmed the presence and retention of a pMOL222-sized plasmid . ID-PCR targeting the RP4-specific trafA gene revealed retention of RP4 for at least 8 weeks . Our findings confirm plasmid transfer and long-term retention in low-carbon-flux, metal-stressed subsurface communities but indicate that the subsurface community examined has limited mobilization potential for the IncQ plasmids employed .
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