The type III protein secretion system contributes to Xanthomonas citri subsp. citri biofilm formation
Sgro, Germán G
Garofalo, Cecilia G
Ficarra, Florencia A
Gehring, Christoph A
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AbstractBackground: Several bacterial plant pathogens colonize their hosts through the secretion of effector proteins by a Type III protein secretion system (T3SS). The role of T3SS in bacterial pathogenesis is well established but whether this system is involved in multicellular processes, such as bacterial biofilm formation has not been elucidated. Here, the phytopathogen Xanthomonas citri subsp. citri (X. citri) was used as a model to gain further insights about the role of the T3SS in biofilm formation. Results: The capacity of biofilm formation of different X. citri T3SS mutants was compared to the wild type strain and it was observed that this secretion system was necessary for this process. Moreover, the T3SS mutants adhered proficiently to leaf surfaces but were impaired in leaf-associated growth. A proteomic study of biofilm cells showed that the lack of the T3SS causes changes in the expression of proteins involved in metabolic processes, energy generation, exopolysaccharide (EPS) production and bacterial motility as well as outer membrane proteins. Furthermore, EPS production and bacterial motility were also altered in the T3SS mutants. Conclusions: Our results indicate a novel role for T3SS in X. citri in the modulation of biofilm formation. Since this process increases X. citri virulence, this study reveals new functions of T3SS in pathogenesis. 2014 Zimaro et al.; licensee BioMed Central Ltd.
CitationZimaro T, Thomas L, Marondedze C, Sgro GG, Garofalo CG, et al. (2014) The type III protein secretion system contributes to Xanthomonas citri subsp. citri biofilm formation. BMC Microbiology 14: 96. doi:10.1186/1471-2180-14-96.
PubMed Central IDPMC4021560
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Insights into xanthomonas axonopodis pv. Citri biofilm through proteomicsZimaro, Tamara; Thomas, Ludivine; Marondedze, Claudius; Garavaglia, Betiana S; Gehring, Christoph A; Ottado, Jorgelina; Gottig, Natalia (Springer Nature, 2013-08-07)Background: Xanthomonas axonopodis pv. Citri (X. a. pv. Citri) causes citrus canker that can result in defoliation and premature fruit drop with significant production losses worldwide. Biofilm formation is an important process in bacterial pathogens and several lines of evidence suggest that in X. a. pv. Citri this process is a requirement to achieve maximal virulence since it has a major role in host interactions. In this study, proteomics was used to gain further insights into the functions of biofilms. Results: In order to identify differentially expressed proteins, a comparative proteomic study using 2D difference gel electrophoresis was carried out on X. a. pv. Citri mature biofilm and planktonic cells. The biofilm proteome showed major variations in the composition of outer membrane proteins and receptor or transport proteins. Among them, several porins and TonB-dependent receptor were differentially regulated in the biofilm compared to the planktonic cells, indicating that these proteins may serve in maintaining specific membrane-associated functions including signaling and cellular homeostasis. In biofilms, UDP-glucose dehydrogenase with a major role in exopolysaccharide production and the non-fimbrial adhesin YapH involved in adherence were over-expressed, while a polynucleotide phosphorylase that was demonstrated to negatively control biofilm formation in E. coli was down-regulated. In addition, several proteins involved in protein synthesis, folding and stabilization were up-regulated in biofilms. Interestingly, some proteins related to energy production, such as ATP-synthase were down-regulated in biofilms. Moreover, a number of enzymes of the tricarboxylic acid cycle were differentially expressed. In addition, X. a. pv. Citri biofilms also showed down-regulation of several antioxidant enzymes. The respective gene expression patterns of several identified proteins in both X. a. pv. Citri mature biofilm and planktonic cells were evaluated by quantitative real-time PCR and shown to consistently correlate with those deduced from the proteomic study. Conclusions: Differentially expressed proteins are enriched in functional categories. Firstly, proteins that are down-regulated in X. a. pv. Citri biofilms are enriched for the gene ontology (GO) terms 'generation of precursor metabolites and energy' and secondly, the biofilm proteome mainly changes in 'outer membrane and receptor or transport'. We argue that the differentially expressed proteins have a critical role in maintaining a functional external structure as well as enabling appropriate flow of nutrients and signals specific to the biofilm lifestyle. 2013 Zimaro et al.; licensee BioMed Central Ltd.
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