Detection and visualization of an exopolysaccharide produced by Xylella fastidiosa in vitro and in planta.

Department of Plant Pathology, University of California, Davis, Davis, CA 95616, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 12/2007; 73(22):7252-8. DOI: 10.1128/AEM.00895-07
Source: PubMed

ABSTRACT Many phytopathogenic bacteria, such as Ralstonia solanacearum, Pantoea stewartii, and Xanthomonas campestris, produce exopolysaccharides (EPSs) that aid in virulence, colonization, and survival. EPS can also contribute to host xylem vessel blockage. The genome of Xylella fastidiosa, the causal agent of Pierce's disease (PD) of grapevine, contains an operon that is strikingly similar to the X. campestris gum operon, which is responsible for the production of xanthan gum. Based on this information, it has been hypothesized that X. fastidiosa is 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 predicted X. fastidiosa EPS polymer. We used enzyme-linked immunosorbent assay to quantify production of EPS from X. fastidiosa cells grown in vitro and immunolocalization microscopy to examine the distribution of X. fastidiosa EPS in biofilms formed in vitro and in planta and assessed the contribution of X. fastidiosa EPS to the vascular occlusions seen in PD-infected grapevines.

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    ABSTRACT: This project focuses on the lipopolysaccharide (LPS) component of the outer membrane of Xylella fastidiosa (Xf). In particular, we are investigating if the O-antigen portion of this molecule contributes to Xf surface attachment and biofilm formation. More importantly, by targeting genes involved in O-antigen biosynthesis, we will determine if LPS is an important virulence factor for Xf infection of grape. Additionally, we will determine if LPS contributes to the high level of host specificity observed for this pathogen. LAYPERSON SUMMARY Xylella fastidiosa (Xf) is a bacterium that has the ability to infect many different plant species. In some plants, this bacterium can cause serious disease. In grapevine, this disease is known as Pierce's disease (PD) and has caused millions of dollars of damage to the California grape industry alone. Xf species also infect other economically important crops such as almond, oleander and citrus. Interestingly, while all Xf isolates belong to the same group or species, some isolates can cause disease in one host but not another. For example, oleander strains cannot cause disease in grapevine and vice versa. One major goal of this project is to understand the bacterial mechanisms that dictate this high level of host specificity. We are focusing on a key component of the bacterial cell membrane, called lipopolysaccharide (LPS), and how certain parts of this molecule may be important in dictating host specificity. We are also investigating how the LPS molecule is related to bacterial virulence and other key aspects of the disease process, like attachment to the plant cell wall. This molecule makes up more than 70% of the bacterial membrane and if LPS does prove to be an important factor during Xf plant infection, its abundance in the bacterial cell membrane makes it a logical target for disease control. Furthermore, antimicrobial compounds that weaken the LPS molecule generally make the bacterium more sensitive to other stresses. Therefore, compounds targeted towards LPS synthesis could increase the efficacy of other anti-Xylella compounds currently being developed when both are used in conjunction.
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    ABSTRACT: Diseases caused by Xylella fastidiosa have attained great importance worldwide as the pathogen and its insect vectors have been disseminated. Since this is the first plant pathogenic bacterium for which a complete genome sequence was determined, much progress has been made in understanding the process by which it spreads within the xylem vessels of susceptible plants as well as the traits that contribute to its acquisition and transmission by sharpshooter vectors. Although this pathogen shares many similarities with Xanthomonas species, such as its use of a small fatty acid signal molecule to coordinate virulence gene expression, the traits that it utilizes to cause disease and the manner in which they are regulated differ substantially from those of related plant pathogens. Its complex lifestyle as both a plant and insect colonist involves traits that are in conflict with these stages, thus apparently necessitating the use of a gene regulatory scheme that allows cells expressing different traits to co-occur in the plant.
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