Previous work from our laboratory showed that the Gram-negative aquatic pathogen Vibrio cholerae can take up a much wider repertoire of fatty acids than other Gram-negative organisms. The current work elaborated on the ability of V. cholerae to exploit an even more diverse pool of lipid nutrients from its environment. We have demonstrated that the bacterium can use lysophosphatidylcholine as a metabolite for growth. Using a combination of thin-layer chromatography and mass spectrometry, we also showed that lysophosphatidylcholine-derived fatty acid moieties can be used for remodeling the V. cholerae membrane architecture. Furthermore, we have identified a lysophospholipase, VolA (Vibrio outer membrane lysophospholipase A), required for these activities. The enzyme is well conserved in Vibrio species, is coexpressed with the outer membrane fatty acid transporter FadL, is one of very few surface-exposed lipoprotein enzymes to be identified in Gram-negative bacteria and the first instance of a surface lipoprotein phospholipase. We propose a model whereby the bacterium efficiently couples the liberation of fatty acid from lysophosphatidylcholine to its subsequent metabolic uptake. An expanded ability to scavenge diverse environmental lipids at the bacterial surface increases overall bacterial fitness and promotes homeoviscous adaptation through membrane remodeling.
(First paragraph) The virulence of Vibrio harveyi, which is a serious pathogen of penaeids (Karunasagar, Pai, Malathi & Karunasagar 1994; Pizzuto & Hirst 1995; Alvarez, Austin, Alvarez & Reyes 1998) and finfish (Kraxberger-Beatty, McGarey, Grier & Lim 1990; Ishimaru & Muroga 1997), has been associated with possession of double haemolysin genes (Zhang, Meaden & Austin 2001). The study seeks to investigate a possible relationship between virulence and the previously described bacteriophage of V. harveyi (Oakey & Owens 2000). The bacteriophage, which has been determined to have an icosahedral head and rigid tail and to contain double stranded linear DNA, has been presumptively assigned to the genus Myovirus (Oakey & Owens 2000)
Immune evasion through membrane remodeling is a hallmark of Yersinia pestis pathogenesis. Yersinia remodels its membrane during its life cycle as it alternates between mammalian hosts (37 °C) and ambient (21 °C to 26 °C) temperatures of the arthropod transmission vector or external environment. This shift in growth temperature induces changes in number and length of acyl groups on the lipid A portion of lipopolysaccharide (LPS) for the enteric pathogens Yersinia pseudotuberculosis (Ypt) and Yersinia enterocolitica (Ye), as well as the causative agent of plague, Yersinia pestis (Yp). Addition of a C16 fatty acid (palmitate) to lipid A by the outer membrane acyltransferase enzyme PagP occurs in immunostimulatory Ypt and Ye strains, but not in immune-evasive Yp. Analysis of Yp pagP gene sequences identified a single-nucleotide polymorphism that results in a premature stop in translation, yielding a truncated, nonfunctional enzyme. Upon repair of this polymorphism to the sequence present in Ypt and Ye, lipid A isolated from a Yp pagP+ strain synthesized two structures with the C16 fatty acids located in acyloxyacyl linkage at the 2′ and 3′ positions of the diglucosamine backbone. Structural modifications were confirmed by mass spectrometry and gas chromatography. With the genotypic restoration of PagP enzymatic activity in Yp, a significant increase in lipid A endotoxicity mediated through the MyD88 and TRIF/TRAM arms of the TLR4-signaling pathway was observed. Discovery and repair of an evolutionarily lost lipid A modifying enzyme provides evidence of lipid A as a crucial determinant in Yp infectivity, pathogenesis, and host innate immune evasion.
Requests for permission to reproduce or translate WHO publications -whether for sale or for non-commercial distribution -should be addressed to WHO Press through the WHO website (www.who.int/about/licensing/copyright_form/en/index.html).The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted and dashed lines on maps represent approximate border lines for which there may not yet be full agreement.The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters.All reasonable precautions have been taken by the World Health Organization to verify the information contained in this publication. However, the published material is being distributed without warranty of any kind, either expressed or implied. The responsibility for the interpretation and use of the material lies with the reader. In no event shall the World Health Organization be liable for damages arising from its use. The report team is grateful to various internal and external reviewers for their useful comments and suggestions on advanced drafts of the main chapters of the report. Particular thanks are due to Michel Beusenberg, Theresa Babovic and Jesus Maria Garcia Calleja from the HIV department in WHO and colleagues from UNAIDS for their careful review of Chapter 6; and to Daniella Cirillo and Tom Shinnick (new TB diagnostics), Cherise Scott and Mel Spigelman (new TB drugs) and Jonathan Daniels, Jennifer Woolley and Tom Evans (new TB vaccines) for their reviews of and input to Chapter 8. Designed by minimum graphicsAnnex 1, which explains how to use the online global TB database, was written by Hazim Timimi. The country profiles that appear in Annex 2, the regional profiles that appear in Annex 3 and the detailed tables showing data for key indicators for all countries in the latest year for which information is available (Annex 4) were also prepared by Hazim Timimi. The online technical appendix that explains the methods used to estimate the burden of disease caused by TB (incidence, prevalence, mortality) was prepared by Philippe Glaziou, with input from Anna Dean, Carel Pretorius, Charalambos Sismanidis and Matteo Zignol. We thank Colin Mathers of the WHO Mortality and Burden of Disease team for his careful review.We thank Pamela Baillie in the Global TB Programme's monitoring and evaluation unit for impeccable administravi n GLOBAL TUBERCULOSIS REPORT 2015 tive support, Doris Ma Fat from the WHO Mortality and Burden of Disease team for providing TB mortality data extracted from the WHO Mortality Da...
bBacterial lipases play important roles in bacterial metabolism and environmental response. Our laboratory recently discovered that a novel lipoprotein lysophospholipase, VolA, localizes on the surface of the Gram-negative aquatic pathogen Vibrio cholerae. VolA functions to cleave exogenous lysophosphatidylcholine, freeing the fatty acid moiety for use by V. cholerae. This fatty acid is transported into the cell and can be used as a nutrient and, more importantly, as a way to alter the membrane architecture via incorporation into the phospholipid biosynthesis pathway. There are few examples of Gram-negative, surface-exposed lipoproteins, and VolA is unique, as it has a previously undercharacterized function in V. cholerae membrane remodeling. Herein, we report the biochemical characterization of VolA. We show that VolA is a canonical lipoprotein via mass spectrometry analysis and demonstrate the in vitro activity of VolA under a variety of conditions. Additionally, we show that VolA contains a conserved Gly-Xaa-Ser-Xaa-Gly motif typical of lipases. Interestingly, we report the observation of VolA homologs in other aquatic pathogens. An Aeromonas hydrophila VolA homolog complements a V. cholerae VolA mutant in growth on lysophosphatidylcholine as the sole carbon source and in enzymatic assays. These results support the idea that the lipase activity of surface-exposed VolA likely contributes to the success of V. cholerae, improving the overall adaptation and survival of the organism in different environments. R ecent work from our laboratory revealed the presence of a unique membrane-anchored lipase, VolA, localized on the surface of Vibrio cholerae cells (1). We demonstrated that VolA is required for growth when lysophosphatidylcholine (LPC) (Fig. 1) serves as the sole carbon source. We hypothesized that VolA could cleave exogenous lysophosphatidylcholine into long-chain fatty acid (LCFA) derivatives (Fig. 1), allowing them to be brought into the cell via a coexpressed fatty acid transporter, FadL. These data, taken together with the presence of a conserved lipase domain identified in V. cholerae (2) and the inability of wild-type V. cholerae to grow on phosphatidylcholine as a sole carbon source, suggest that VolA acts as a lysophospholipase in vivo.Phospholipases are members of the acylhydrolase family of enzymes, acting on ester bonds in phospholipid targets (3). The structure and function of such acylhydrolases are conserved and have been well studied. All contain a characteristic fold (4, 5), sharing a conserved lipase motif (2). In our previous work (1), we noted that VolA contains this conserved motif, which strongly implicates it as a lipase. Phospholipases vary in terms of their site of action on the phospholipid. Some target phosphate bonds, while others hydrolyze bonds between the glycerol moiety and the acyl chains. Most microbial lysophospholipases hydrolyze the ester bond between the acyl chain and the polar head group, releasing a free fatty acid (6). It is likely that VolA functions similarly to e...
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