Although the antimicrobial effects of silver salts were noticed long ago, the molecular mechanism of the bactericidal action of Ag ؉ in low concentrations has not been elucidated. Here, we show that low concentrations of Ag ؉ induce a massive proton leakage through the Vibrio cholerae membrane, which results in complete deenergization and, with a high degree of probability, cell death.

The production of several virulence factors in Vibrio cholerae O1, including cholera toxin and the pilus colonization factor TCP (toxin-coregulated pilus), is strongly influenced by environmental conditions. To specifically identify membrane proteins involved in these signal transduction events, we examined a transposon library of V. cholerae generated by Tnbla mutagenesis for cells that produce TCP when grown under various nonpermissive conditions. To select for TCP-producing cells we used the recently described bacteriophage CTX⌽-Kan, which uses TCP as its receptor and carries a gene encoding resistance to kanamycin. Among the isolated mutants was a transposon insertion in a gene homologous to nqrB from Vibrio alginolyticus, which encodes a subunit of a Na ؉ -translocating NADH:ubiquinone oxidoreductase, and tcpI, encoding a chemoreceptor previously implicated in the negative regulation of TCP production. A third transposon mutant had an insertion in tcpP, which is in an operon with tcpH, a known positive regulator of TCP production. However, TcpP was shown to be essential for TCP production in V. cholerae, as a tcpP-deletion strain was deficient in pili production. The amino-terminal region of TcpP shows sequence homology to the DNA-binding domains of several regulatory proteins, including ToxR from V. cholerae and PsaE from Yersinia pestis. Like ToxR, TcpP activates transcription of the toxT gene, an essential activator of tcp operon transcription. Furthermore, TcpH, with its large periplasmic domain and inner membrane anchor, has a structure similar to that of ToxS and was shown to enhance the activity of TcpP. We propose that TcpP͞TcpH constitute a pair of regulatory proteins functionally similar to ToxR͞ToxS and PsaE͞PsaF that are required for toxT transcription in V. cholerae.Vibrio cholerae is a Gram-negative bacterium that causes the diarrheal disease cholera. To establish infection and cause disease, V. cholerae must express a variety of virulence factors, including cholera toxin (CT) and colonization factors such as the toxin-coregulated pilus (TCP). Expression of CT and TCP is strongly influenced by environmental stimuli, including temperature, pH, osmolarity, and composition of the growth medium (1-3). The mechanisms by which environmental conditions affect the coordinate expression of virulence factors by V. cholerae remain poorly understood but certainly involve transcriptional regulation mediated by several regulatory proteins (4, 5). The current model for virulence regulation is that of a cascade in which ToxR controls expression of ToxT, which itself is a transcriptional activator and directly controls expression of several virulence genes (5). ToxR is an inner membrane protein that contains a cytoplasmic DNA-binding domain with homology to the OmpR subfamily of the regulator proteins of the twocomponent signal transduction family (6). The periplasmic domain of ToxR is thought to interact with another transmembrane regulatory protein, ToxS, that stimulates its activity (7). ToxR, in co...

An outbreak of stony coral tissue loss disease (SCTLD), emerged on reefs off the coast of southeast Florida in 2014 and continues to spread throughout Florida's Reef Tract. SCTLD is causing extensive mortality of multiple coral species and disease signs vary among affected coral species with differences in rates of tissue loss (acute and subacute), lesion morphology (adjacent bleached zone or not) and lesion occurrence (focal and multi-focal). We examined the virulence, transmission dynamics and response to antibiotic treatment of coral species exhibiting different types of tissue loss lesions from two regions in Florida. Montastraea cavernosa with subacute tissue loss lesions in the southeast Florida region near Fort Lauderdale was compared to corals (multiple species) with acute tissue loss lesions in the Middle Keys. Corals from both regions showed progressive tissue loss but the in situ rate of mortality was significantly higher in tagged colonies in the Keys. Aquaria studies showed disease transmission occurred through direct contact and through the water column for corals from both regions. However, transmission success was higher for corals with acute vs. subacute lesions. There was 100% transmission for both test species, M. cavernosa and Meandrina meandrites, touching acute lesions. Among the three species touching subacute lesions, the disease transmitted readily to Orbicella faveolata (100%) followed by M. cavernosa (30%) with no transmission occurring with Porites astreoides. Diseased fragments of all species tested responded to antibiotic treatment with a cessation or slowing of the disease lesions suggesting that bacteria are involved in disease progression. Mortality was higher for in situ corals with acute lesions and transmission was higher in M. cavernosa exposed to acute lesions compared to subacute lesions, suggesting that different microbes may be involved with the two lesion types. However, since in situ mortality of M. cavernosa was not measured in the Middle Keys, we cannot completely rule out that a common pathogen is involved but is less virulent within M. cavernosa.

No abstract

The large mechanosensitive ion channel (MscL) of Escherichia coli was expressed on a plasmid encoding MscL as a fusion protein with glutathione S-transferase in an Escherichia coli strain containing a disruption in the chromosomal mscL gene. After purification of the fusion protein using glutathione-coated beads, thrombin cleavage allowed recovery of the MscL protein. The purified protein was reconstituted into artificial liposomes and found to be fully functional when examined with the patch-clamp technique. The reconstituted recombinant MscL protein formed ion channels that exhibited characteristic conductance and pressure sensitivity and were blocked by the mechanosensitive ion channel inhibitor gadolinium. The recombinant MscL protein was also used to raise specific anti-MscL polyclonal antibodies which abolished channel activity when preincubated with the MscL protein.

During 2006 and 2007, we documented the re-emergence of severe episodes of vibriosis caused by Vibrio tubiashii in shellfish hatcheries on the west coast of North America. Lost larval and juvenile production included 3 previously undescribed hosts, Pacific (Crassostrea gigas) and Kumamoto (C. sikamea) oysters and geoduck clams Panope abrupta, with a 2007 decline in larval oyster production of ~59% in one hatchery. Losses of larval and juvenile bivalves were linked to V. tubiashii blooms in the coastal environment, which were associated with the apparent mixing of unusually warm surface seawater and intermittently upwelled cooler, nutrient-and Vibrio spp.-enriched seawater. The ocean temperature elevation anomaly in 2007 was not clearly linked to an El Niño event, as was a similar episode in 1998. Concentrations of the dominant shellfish-pathogenic vibrios were as high as 1.6 × 10 5 cfu ml -1 in the cold, upwelled water. The bacteria possessed the genes coding for a protease and hemolysin described for V. tubiashii, and pathogenic isolates secreted these peptides. Lesions resulting from a classic invasive disease and a toxigenic noninvasive disease occurred in oyster and geoduck clam larvae. Management and prevention require reduction of incoming concentrations of the bacteria, reduction of contamination in water and air supplies and in stock chemical solutions, removal of bacterial toxins, and interruption of the cycle of bacterial amplification in the hatchery and in microalgal food supplies.

Analysis of the bacterial genome sequences shows that many human and animal pathogens encode primary membrane Na+ pumps, Na+-transporting dicarboxylate decarboxylases or Na+-translocating NADH:ubiquinone oxidoreductase, and a number of Na+-dependent permeases. This indicates that these bacteria can utilize Na+ as a coupling ion instead of or in addition to the H+ cycle. This capability to use a Na+ cycle might be an important virulence factor for such pathogens as Vibrio cholerae, Neisseria meningitidis, Salmonella enterica serovar Typhi, and Yersinia pestis. In Treponema pallidum, Chlamydia trachomatis, and Chlamydia pneumoniae, the Na+ gradient may well be the only energy source for secondary transport. A survey of preliminary genome sequences of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Treponema denticola indicates that these oral pathogens also rely on the Na+ cycle for at least part of their energy metabolism. The possible roles of the Na+ cycling in the energy metabolism and pathogenicity of these organisms are reviewed. The recent discovery of an effective natural antibiotic, korormicin, targeted against the Na+-translocating NADH:ubiquinone oxidoreductase, suggests a potential use of Na+ pumps as drug targets and/or vaccine candidates. The antimicrobial potential of other inhibitors of the Na+ cycle, such as monensin, Li+ and Ag+ ions, and amiloride derivatives, is discussed

As many as 22 of the 45 coral species on the Florida Reef Tract are currently affected by stony coral tissue loss disease (SCTLD). The ongoing disease outbreak was first observed in 2014 in Southeast Florida near Miami and as of early 2019 has been documented from the northernmost reaches of the reef tract in Martin County down to Key West. We examined the microbiota associated with disease lesions and apparently healthy tissue on diseased colonies of Montastraea cavernosa, Orbicella faveolata, Diploria labyrinthiformis, and Dichocoenia stokesii. Analysis of differentially abundant taxa between disease lesions and apparently healthy tissue identified five unique amplicon sequence variants enriched in the diseased tissue in three of the coral species (all except O. faveolata), namely an unclassified genus of Flavobacteriales and sequences identified as Fusibacter (Clostridiales), Planktotalea (Rhodobacterales), Algicola (Alteromonadales), and Vibrio (Vibrionales). In addition, several groups of likely opportunistic or saprophytic colonizers such as Epsilonbacteraeota, Patescibacteria, Clostridiales, Bacteroidetes, and Rhodobacterales were also enriched in SCTLD disease lesions. This work represents the first microbiological characterization of SCTLD, as an initial step toward identifying the potential pathogen(s) responsible for SCTLD.