- pVC, a Small Cryptic Plasmid from the Environmental Isolate of Vibrio cholerae MP-1
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Ruifu Zhang , Yanling Wang , Pak Chow Leung , Ji-Dong Gu
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J. Microbiol. 2007;45(3):193-198.
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DOI: https://doi.org/2543 [pii]
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A marine bacterium was isolated from Mai Po Nature Reserve of Hong Kong and identified as Vibrio cholerae MP-1. It contains a small plasmid designated as pVC of 3.8 kb. Four open reading frames (ORFs) are identified on the plasmid, but none of them shows homology to any known protein. Database search indicated that a 440 bp fragment is 96% identical to a fragment found in a small plasmid of another V. cholerae. Further experiments demonstrated that a 2.3 kb EcoRI fragment containing the complete ORF1, partial ORF4 and their intergenic region could self-replicate. Additional analyses revealed that sequence upstream of ORF1 showed the features characteristic of theta type replicons. Protein encoded by ORF1 has two characteristic motifs existed in most replication initiator proteins (Rep): the leucine zipper (LZ) motif located at the N-terminal region and the alpha helix-turn-alpha helix motif (HTH) located at the C-terminal end. The results suggest that pVC replicates via the theta type mechanism and is likely a novel type of theta replicon.
- Bacterial Color Response to Hexavalent Chromium, Cr^6+
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Ka Hong Cheung , Ji-Dong Gu
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J. Microbiol. 2002;40(3):234-236.
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A blue pigment-producing bacterium, Vogesella indigofera, was isolated and quantified for the relationship between its synthesis of a blue pigment and exposure concentrations of Cr^6+ . The concentration of Cr^6+ and the percentage of blue colonies on agar plates was negatively correlated (r^2 = -0.8683). Critical concentrations inhibiting bacterial pigment production were found to be between 100-150 ug Cr^6+ /ml on agar plates and 200-300 ug Cr^6+ /ml in liquid culture. As the blue color is characteristic and easily observable, the bacterium Vogesella indigofera may have potential applications in the detection and monitoring of environmental pollution.
- Antagonism of Bacterial Extracellular Metabolites to Freshwater-Fouling Invertebrate Zebra Mussels, Dreissena polymorpha
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Ji-Dong Gu , Ralph Mitchell
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J. Microbiol. 2001;39(2):133-138.
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We investigated the antagonism of indigenous bacteria isolated from stressed mussels and their extra-cellular metabolites on the adult zebra mussel, Dreissena polymorpha. Selective bacterial isolates including Aeromonas media, A. salmonicida, A. veronii, and Shewanella putrefaciens, showed strong lethality against adult mussels and 100% mortality was observed within 5 days of incubation. Bacterial metabolites, fractionated and concentrated from stationary-phase culture supernatants of these bacterial isolates, displayed varying degrees of antagonistic effects on zebra mussels. Among the three size fractions examined, <5, 5-10, and >10 kDa, the most lethal fraction seems to be >10 kDa for three of the four isolates tested. Further chemical analyses of these size fractions revealed that the predominant constituents were polysaccharides and proteins. No 2-keto-3-deoxyoctanoic acid (2-KDO), deoxyri-bonucleic acids (DNA) or uronic acid were detectable. Extraction of supernatants of two antagonistic isolates with polar solvent suggested that polar molecules are present in the active fraction. Our data suggest that extracellular metabolites produced by antagonistic bacteria are also involved in disease development in zebra mussels and elucidation of the mechanisms involved may offer a novel strategy for control of biofouling invertebrates.
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