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The fish pathogen Aliivibrio salmonicida LFI1238 can degrade and utilize chitin as a nutrient source despite major gene loss in the chitinolytic pathway

ABSTRACT: The marine bacterium Aliivibriosalmonicida (formerly Vibrio salmonicida) is the causative agent of cold water vibriosis, a disease that led to severe losses in Norwegian aquaculture during the 1980s. Genes encoding a glycoside hydrolase family 18 (GH18) chitinase and two lytic polysaccharide monooxygenases (LPMOs) containing chitin binding domains are encoded in the genome of this bacterium, indicating a chitin degrading capability. However, due to extensive gene decay, some parts of the chitinolytic pathways are believed to be dysfunctional. To investigate the chitinolytic abilities of the bacterium, we combined microbiological and biochemical experiments with proteomic analysis. The family GH18 chitinase was able to depolymerize - and -chitin, but its activity was up to 50-fold lower compared to other well-studied chitinases from Serratia marcescens and Cellvibrio japonicus. The two LPMOs showed activity on chitin, cleaving the substrate chains by oxidation. Cultivation experiments showed that Al. salmonicida was able to grow on and utilize the soluble building blocks of chitin; N-acetyl-D-glucosamine (GlcNAc) and chitobiose (GlcNAc2). Furthermore, cultivation and gene deletion studies revealed that the bacterium was able to degrade insoluble chitin, albeit at a slow rate, and that growth on this substrate was dependent on the GH18 chitinase, but to a lesser extent the LPMOs. Finally, expression of the GH18 chitinase and both LPMOs was detected by proteomic analysis of Al. salmonicida cultivated on chitin as the sole carbon source. In conclusion, our results show that Al. salmonicida LFI1238 can utilize chitin as source of nutrients and its ability depends on the GH18 chitinase.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Aliivibrio Salmonicida Lfi1238

SUBMITTER: Magnus Arntzen

LAB HEAD: Gustav Vaaje-Kolstad

PROVIDER: PXD021397 | Pride | 2021-07-26

REPOSITORIES: Pride

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Project description:Background Aeromonas salmonicida subsp. salmonicida, the etiologic agent of furunculosis, is a major pathogen of fisheries worldwide. Despite the identification of several virulence factors the pathogenesis is still poorly understood. We have used high-throughput proteomics to display the differences between in vitro secretome of A. salmonicida wild-type (wt, hypervirulent, JF5054) and T3SS-deficient (isogenic DeltaascV, extremely low-virulent, JF2747) strains in exponential (GP) and stationary (SP) phases of growth. Results Among the different experimental conditions we obtained semi-quantitative values for a total of 2136 A. salmonicida proteins. Proteins of specific A. salmonicida species were proportionally less detected than proteins common to the Aeromonas genus or those shared with other Aeromonas species, suggesting that in vitro growth did not induce the expression of these genes. Four detected proteins which are unidentified in the genome of reference strains of A. salmonicida were homologous to components of the conjugative T4SS of A. hydrophila pRA1 plasmid. Polypeptides of three proteins which are specific to the 01-B526 strain were also discovered. In supernatants (SNs), the number of detected proteins was higher in SP (326 for wt vs 329 for mutant) than in GP (275 for wt vs 263 for mutant). In pellets, the number of identified proteins (a total of 1536) was approximately the same between GP and SP. Numerous highly conserved cytoplasmic proteins were present in A. salmonicida SNs (mainly EF-Tu, EF-G, EF-P, EF-Ts, TypA, AlaS, ribosomal proteins, HtpG, DnaK, peptidyl-prolyl cis-trans isomerases, GAPDH, Enolase, FbaA, TpiA, Pgk, TktA, AckA, AcnB, Mdh, AhpC, Tpx, SodB and PNPase), and several evidences support the theory that their extracellular localization was not the result of cell lysis. According to the Cluster of Orthologous Groups classification, 29% of excreted proteins in A. salmonicida SNs were currently poorly characterized. Conclusions In this part of our work we elucidated the whole in vitro exoproteome of hypervirulent A. salmonicida subsp. salmonicida and showed the secretion of several highly conserved cytoplasmic proteins with putative moonlighting functions and roles in virulence. All together, our results offer new information about the pathogenesis of furunculosis and point out potential candidates for vaccine development.

Project description:Aeromonas salmonicida is a fish pathogen that causes furunculosis. Virulent strains of this bacterium are able to infect salmonid macrophages and survive within them, although mechanisms favouring intracellular survival are not completely understood. It is known that A. salmonicida cultured in vivo in the peritoneal cavity of the host undergoes changes in gene expression and surface architecture compared with cultures grown in vitro in broth. Therefore, in this study, the macrophage responses to A. salmonicida grown in vivo and in vitro were compared. Enriched macrophages isolated from head kidney of Atlantic salmon (Salmo salar) were infected in vitro in 96-well microtitre dishes and changes in gene expression during the infection process were monitored using a custom Atlantic salmon cDNA microarray. A. salmonicida cultures grown in tryptic soy broth and in peritoneal implants were used to infect the macrophages. The macrophages were harvested at 0.5, 1.0 and 2.0 h after addition of the bacteria to the medium. Significant changes in gene expression were evident by microarray analysis at 2.0 h post-infection in macrophages infected with broth-grown and implant-grown bacteria; however, qPCR analysis revealed earlier up-regulation of JunB and TNF-alpha in macrophages exposed to the implant-grown bacteria. Up-regulation of those genes and others is consistent with the effects of extracellular products of aeromonad bacteria on macrophages and also suggests initiation of the innate immune response. Keywords: time course Enriched macrophages from 24 responder fish that showed positive respiratory burst in response to phorbol myristate acetate were plated in individual wells of 96-well flat-bottom polystyrene tissue culture plates. A. salmonicida were added to the macrophages, and incubated for 0.5, 1.0 or 2.0 h. Control wells received 10 ul of HBSS. Three replicate infections were performed for each type of bacteria. Hybridizations were carried out in duplicate, reversing the fluors for each sample on the second chip.

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The fish pathogen Aliivibrio salmonicida LFI1238 can degrade and utilize chitin as a nutrient source despite major gene loss in the chitinolytic pathway

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