Xanthan Pyruvilation Is Essential for the Virulence of Xanthomonas campestris pv. campestris

Abstract

Xanthan, the main exopolysaccharide (EPS) synthesized by Xanthomonas spp., contributes to bacterial stress tolerance and enhances attachment to plant surfaces by helping in biofilm formation. Therefore, xanthan is essential for successful colonization and growth in planta and has also been proposed to be involved in the promotion of pathogenesis by calcium ion chelation and, hence, in the suppression of the plant defense responses in which this cation acts as a signal. The aim of this work was to study the relationship between xanthan structure and its role as a virulence factor. We analyzed four Xanthomonas campestris pv. campestris mutants that synthesize structural variants of xanthan. We found that the lack of acetyl groups that decorate the internal mannose residues, ketal-pyruvate groups, and external mannose residues affects bacterial adhesion and biofilm architecture. In addition, the mutants that synthesized EPS without pyruvilation or without the external mannose residues did not develop disease symptoms in Arabidopsis thaliana. We also observed that the presence of the external mannose residues and, hence, pyruvilation is required for xanthan to suppress callose deposition as well as to interfere with stomatal defense. In conclusion, pyruvilation of xanthan seems to be essential for Xanthomonas campestris pv. campestris virulence.

Xanthomonas vesicatoria virulence factors involved in early stages of bacterial spot development in tomato

“…During their epiphytic life many plant pathogenic bacteria form biofilms, a strategy that allows them to cope with harsh environments and establish pathogenic interactions with their hosts (Castiblanco & Sundin, ). In other Xanthomonas species, biofilm establishment requires, among other factors, the production of xanthan (Rigano et al ., ; Bianco et al ., ), and the presence of flagella (Malamud et al ., ) and T4P (Dunger et al ., ). In this study, the most aggressive strain, BNM 208, developed a biofilm with mature characteristics, with defined cell clusters, a homogeneous and compact structure, high biomass and substratum coverage.…”

“…Bacterial tolerance to these stressful conditions is often associated with the formation of biofilms. These structures have been related to virulence in different Xanthomonas species (Yaryura et al ., ; Bianco et al ., ).…”

“…EPSs are needed to form an intricate and complex three‐dimensional matrix, which provides structural support for bacterial biofilms. This contributes to epiphytic survival before colonization of the host plant and is essential for bacterial virulence and disease progression (Yun et al ., ; Aslam et al ., ; Bianco et al ., ).…”

“…The ability to form biofilms has been related to virulence in other Xanthomonas species (Darsonval et al ., ; Yaryura et al ., ; Bianco et al ., ). Biofilm formation and motility are well described for many plant pathogenic bacteria, but these virulence factors are understudied in Xv.…”

Systems and synthetic biology perspective of the versatile plant-pathogenic and polysaccharide-producing bacterium Xanthomonas campestris

“…General functions attributed to exopolysaccharides like xanthan are protection against external stress factors such as radiation [55], varying pH values, high salt concentrations and drought [56,57]. Xanthan pyruvylation is essential for the virulence of Xcc [58]. Xanthan is not essential for the infection of citrus plants but it contributes to the epiphytic survival of the pathogen [59].…”