The phosphate-starvation response in Vibrio cholerae O1 and phoB mutant under proteomic analysis: disclosing functions involved in adaptation, survival and virulence

A proteomic analysis of a wild-type and of a phoB mutant showed that Vibrio cholerae expresses genes of two major regulons in response to phosphate starvation. The Pho regulon, expressed by the wild-type, allowed the cells to adapt to the new environment. Induction of the general stress regulon was mainly observed in the phoB mutant as a strategy to resist stress and survive. Some functions of the adaptative and survival responses play roles in the pathogenicity of the bacteria. Among the members of the Pho regulon, we found a porin described as an important factor for the intestinal colonisation. Other functions not obviously related to phosphate metabolism, expressed preferentially by the wild-type cells, have also been implicated in virulence. These findings might explain the lack of virulence of the phoB mutant. The Pho regulon picture of V. cholerae, however, will not be complete until minor members and membrane proteins are identified. Among the phosphate-starvation induced genes we have found 13 hypothetical ones and for some of them functions have been assigned. The majority of the genes identified here have not been described before, thus they could be used to expand the proteomic reference map of V. cholerae El Tor.     

The cell biology of Listeria monocytogenes infection: the intersection of bacterial pathogenesis and cell-mediated immunity

Listeria monocytogenes has emerged as a remarkably tractable pathogen to dissect basic aspects of cell biology, intracellular pathogenesis, and innate and acquired immunity. In order to maintain its intracellular lifestyle, L. monocytogenes has evolved a number of mechanisms to exploit host processes to grow and spread cell to cell without damaging the host cell. The pore-forming protein listeriolysin O mediates escape from host vacuoles and utilizes multiple fail-safe mechanisms to avoid causing toxicity to infected cells. Once in the cytosol, the L. monocytogenes ActA protein recruits host cell Arp2/3 complexes and enabled/vasodilator-stimulated phosphoprotein family members to mediate efficient actin-based motility, thereby propelling the bacteria into neighboring cells. Alteration in any of these processes dramatically reduces the ability of the bacteria to establish a productive infection in vivo.     

Two-component signal transduction systems and regulation of virulence factors in <Emphasis Type=Italic>Xanthomonas</Emphasis>: a perspective

Two-component signal transduction systems (TCSTSs), consisting of a histidine kinase and a response regulator, play a critical role in regulating virulence gene expression in Gram-negative phytopathogenic bacteria Xanthomonas spp.. To date, 12 TCSTS genes have been identified, accounting for approximately 10% of the TCSTS genes in each genome that have been experimentally identified to be related to pathogenesis. These TCSTSs modulate the expression of a number of virulence factors through diverse molecular mechanisms such as interacting with DNA, protein-binding and involvement in second messenger metabolism, which generates a high level of regulatory versatility. Here we summarize the current knowledge in this field and discuss the emerging themes and remaining questions that are important in deciphering the signaling network of TCSTSs in Xanthomonas.     

Quorum sensing and fungal–bacterial interactions in Candida albicans: a communicative network regulating microbial coexistence and virulence

Microorganisms have evolved a complex signature of communication termed quorum sensing (QS), which is based on the exchange and sensing of low-molecular-weight signal compounds. The ability to communicate within the microbial population gives the advantage to coordinate a groups behaviour leading to a higher fitness in the environment. The polymorphic fungus Candida albicans is an opportunistic human pathogen able to regulate virulence traits through the production of at least two QS signal molecules: farnesol and tyrosol. The ability to adopt multiple morphotypes and form biofilms on infected surfaces are the most important pathogenic characteristics regulated by QS and are of clinical relevance. In fact, traditional antimicrobial approaches are often ineffective towards these characteristics. Moreover, the intimate association between C. albicans and other pathogens, such as Pseudomonas aeruginosa , increases the complexity of the infection system. This review outlines the current knowledge on fungal QS and fungal–bacterial interactions emphasizing on C. albicans . Further investigations need to concentrate on the molecular mechanisms and the genetic regulation of these phenomena in order to identify putative novel therapeutic options.     

Molecular cloning and nucleotide sequencing of oxyR, the positive regulatory gene of a regulon for an adaptive response to oxidative stress in Escherichia coli: homologies between OxyR protein and a family of bacterial activator proteins

Summary Treatment of Escherichia coli and Salmonella typhimurium cells with a low dose of hydrogen peroxide induces expression of a large number of genes, and confers resistance to oxidative stresses. The oxyR gene encodes a positive regulatory protein for a subset of these genes involved in the defense against oxidative damage. We cloned a DNA fragment that contains the E. coli oxyR region on a plasmid vector, and analyzed the nucleotide sequence of the gene. The amino acid sequence of OxyR protein, deduced from the nucleotide sequence, shows a high degree of homology to the sequences of a number of bacterial activator proteins including LysR, cysB, IlvY, MetR and NodD. The product of the oxyR gene identified by the maxicell procedure was a 34 kDa protein, which agrees with the size predicted from the nucleotide sequence of the gene.     

The application of the herbicide bromoxynil to a model soil-derived bacterial community: impact on degradation and community structure

AIMS: Bromoxynil degradation by soil micro-organisms has been shown to be co-oxidative in character. In this study, we investigate both the impact of the application of increasing bromoxynil concentrations on soil-derived bacterial communities and how these changes are reflected in the degradation of the compound. Our aim was to test the hypothesis that the addition of bromoxynil to a soil-derived bacterial community, and the availability of a readily utilizable carbon source would have an impact on bromoxynil degradation, and that would be reflected in the bacteria present in the soil community. METHODS AND RESULTS: Degradation of bromoxynil was observed in soil-derived communities containing 15 mg l(-1), but not 50 mg l(-1) of the compound, unless glucose was added. This suggests that the addition of carbon stimulates co-oxidative bromoxynil degradation by the members of the bacterial community. Measurable changes in the bacterial community indicated that the addition of bromoxynil led to deterministic selection on the bacterial population, i.e. the communities observed arise through the selection of specific micro-organisms that are best adapted to the conditions in the soil. The addition of bromoxynil was also shown to have a negative impact on the presence of alpha and gamma-proteobacteria in the soil community. CONCLUSION: Bromoxynil degradation is significantly inhibited in bacterial soil communities in the absence of readily accessible carbon. The application of bromoxynil appears to exert deterministic selection on the bacterial community. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the effects of increasing bromoxynil concentrations on a model bacterial population derived from soil. Soil communities show qualitative and quantitative differences to bromoxynil application depending on the availability of organic carbon. These findings might have implications for the persistence of bromoxynil in agricultural soils.