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.