Detection and Visualization of an Exopolysaccharide Produced byXylella fastidiosaIn Vitro and In Planta

Abstract

Many phytopathogenic bacteria, such asRalstonia solanacearum,Pantoea stewartii, andXanthomonas campestris, produce exopolysaccharides (EPSs) that aid in virulence, colonization, and survival. EPS can also contribute to host xylem vessel blockage. The genome ofXylella fastidiosa, the causal agent of Pierce's disease (PD) of grapevine, contains an operon that is strikingly similar to theX. campestris gumoperon, which is responsible for the production of xanthan gum. Based on this information, it has been hypothesized thatX. fastidiosais capable of producing an EPS similar in structure and composition to xanthan gum but lacking the terminal mannose residue. In this study, we raised polyclonal antibodies against a modified xanthan gum polymer similar to the predictedX. fastidiosaEPS polymer. We used enzyme-linked immunosorbent assay to quantify production of EPS fromX. fastidiosacells grown in vitro and immunolocalization microscopy to examine the distribution ofX. fastidiosaEPS in biofilms formed in vitro and in planta and assessed the contribution ofX. fastidiosaEPS to the vascular occlusions seen in PD-infected grapevines.