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A Novel Alpha-Proteobacterium Resides in the Mitochondria of Ovarian Cells of the Tick Ixodes ricinus. Tiziana Beninati, 2004.An intracellular bacterium from Ixodes ricinus ticks collected in Italy was characterized by electron microscopy (EM), PCR sequencing of the 16S rRNA gene, molecular phylogenetic analysis, and in situ hybridization (ISH) . This bacterium was shown by EM to be present in the cytoplasm, as well as in the mitochondria of ovarian cells . When universal 16S rRNA bacterial primers were used, PCR amplification of ovarian DNA followed by cloning and sequencing resulted in the same sequence being found in each sample . Phylogenetic analysis of this sequence showed that the bacterium from which it was derived, tentatively designated IricES1, is part of a novel clade in the alpha subdivision of the Proteobacteria . ISH and PCR assays of various tissues performed with oligonucleotides specific for the IricES1 16S rRNA showed that IricES1 is restricted to ovarian cells . Based on the results obtained, we inferred that the bacteria seen by EM in ovarian cells are a single type of bacteria, corresponding to IricES1 . PCR screening of 166 ticks from various parts of Italy and one site in England showed that IricES1 was present in 96% of adult females and 44% of nymphs (unsexed) . No adult males were found to be infected . Despite the apparent parasitism of host mitochondria by IricES1, the available information suggests that the bacterium has an obligate relationship with its host, although this must be confirmed . New Class of IMP Cyclohydrolases in Methanococcus jannaschii. Marion Graupner, 2002.The enzyme responsible for observed IMP cyclohydrolase activity in Methanococcus jannaschii was purified and sequenced: its genetic locus was found to correspond to gene MJ0626 . The MJ0626 gene was cloned, and its protein product was expressed in Escherichia coli and shown to catalyze the cyclization of 5-formylamidoimidazole-4-carboxamide ribonucleotide to IMP . The enzyme has no sequence similarity to known enzymes, and its catalytic properties appear distinct from any characterized IMP cyclohydrolase . The purO gene for the enzyme is currently found only in the domain Archaea . Characterization of Dominantly Negative Mutant ClyA Cytotoxin Proteins in Escherichia coli. Sun Nyunt Wai, 2003.We report studies of the subcellular localization of the ClyA cytotoxic protein and of mutations causing defective translocation to the periplasm in Escherichia coli . The ability of ClyA to translocate to the periplasm was abolished in deletion mutants lacking the last 23 or 11 amino acid residues of the C-terminal region . A naturally occurring ClyA variant lacking four residues (183 to 186) in a hydrophobic subdomain was retained mainly in the cytosolic fraction . These mutant proteins displayed an inhibiting effect on the expression of the hemolytic phenotype of wild-type ClyA . Studies in vitro with purified mutant ClyA proteins revealed that they were defective in formation of pore assemblies and that their activity in hemolysis assays and in single-channel conductance tests was at least 10-fold lower than that of the wild-type ClyA . Tests with combinations of the purified proteins indicated that mutant and wild-type ClyA interacted and that formation of heteromeric assemblies affected the pore-forming activity of the wild-type protein . The observed protein-protein interactions were consistent with, and provided a molecular explanation for, the dominant negative feature of the mutant ClyA variants . Temperature-Regulated Bleaching and Lysis of the Coral Pocillopora damicornis by the Novel Pathogen Vibrio coralliilyticus. Yael Ben-Haim, 2003.Coral bleaching is the disruption of symbioses between coral animals and their photosynthetic microalgal endosymbionts (zooxanthellae) . It has been suggested that large-scale bleaching episodes are linked to global warming . The data presented here demonstrate that Vibrio coralliilyticus is an etiological agent of bleaching of the coral Pocillopora damicornis . This bacterium was present at high levels in bleached P . damicornis but absent from healthy corals . The bacterium was isolated in pure culture, characterized microbiologically, and shown to cause bleaching when it was inoculated onto healthy corals at 25°C . The pathogen was reisolated from the diseased tissues of the infected corals . The zooxanthella concentration in the bacterium-bleached corals was less than 12% of the zooxanthella concentration in healthy corals . When P . damicornis was infected with V . coralliilyticus at higher temperatures (27 and 29°C), the corals lysed within 2 weeks, indicating that the seawater temperature is a critical environmental parameter in determining the outcome of infection . A large increase in the level of the extracellular protease activity of V . coralliilyticus occurred at the same temperature range (24 to 28°C) as the transition from bleaching to lysis of the corals . We suggest that bleaching of P . damicornis results from an attack on the algae, whereas bacterium-induced lysis and death are promoted by bacterial extracellular proteases . The data presented here support the bacterial hypothesis of coral bleaching .
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