|RAPICAVOLI, JEANNETTE - University Of California
|KINSINGER, NICHOLA - University Of California
|PERRING, THOMAS - University Of California
|SHUGART, HOLLY - University Of Florida
|JOHNSTON, CRYSTAL - University Of California
|WALKER, SHARON - University Of California
|ROPER, CAROLINE - University Of California
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2015
Publication Date: 9/18/2015
Citation: Rapicavoli, J.N., Kinsinger, N., Perring, T., Backus, E.A., Shugart, H., Johnston, C.M., Walker, S., Roper, C. 2015. Lipopolysaccharide modulates the vector-pathogen interface of the xylem-limited phytopathogen, Xylella fastidiosa, the causal agent of Pierce’s disease of grapevine. Applied and Environmental Microbiology. 81:8145-8154.
Interpretive Summary: Pierce’s disease, caused by the bacterium Xylella fastidiosa, is one of the most economically important diseases of grape in California and other parts of the U.S. The bacteria are spread by feeding of sharpshooter vectors and other piercing-sucking insects. Bacteria are acquired from infected plants during feeding; bacteria adhere to surfaces of the foregut, multiply, and then are expelled outward during later feeding. Development of new disease management methods is difficult, in part because the mechanisms of acquisition and inoculation of X. fastiosa by sharpshooters are not well understood. Present research focuses on the role of lipopolysaccharide (LPS) in early stages of X. fastidiosa acquisition by insect vectors. LPS is an abundant molecule on the cell surface of X. fastidiosa that is thought to play a role in bacterial interactions with the environment, insect vectors, and host plants. Wild type versus mutated bacteria producing altered LPS were included in artificial diets fed to an efficient insect vector, the blue-green sharpshooter. Results showed that changes in LPS structure caused a change in physiochemical properties of the cell surface, which in turn significantly affected attachment of X. fastidiosa to vector foreguts. Scanning electron microscopy confirmed that this defect in initial attachment prevents biofilm formation within vector foreguts, impairing pathogen acquisition. Thus, the present results demonstrate that LPS impacts the pathogen-vector interaction during in the transmission process. Information from this research could be exploited for development of a new disease management tactic.
Technical Abstract: Xylella fastidiosa Wells et al. is a gram-negative, insect-transmitted bacterium that causes a lethal disease of grapevine called Pierce’s disease. Lipopolysaccharide (LPS) is the most dominant macromolecule displayed on the cell surface of gram-negative bacteria. Bacterial interactions with the environment and potential hosts are mediated by LPS. LPS is comprised of a highly conserved Lipid A-Core Oligosaccharide component, and a variable O-antigen of polysaccharide chains. In this study, artificial diets for insects were used to determine the contribution of LPS to early steps of X. fastidiosa acquisition by an efficient insect vector, the blue-green sharpshooter (Graphocephala atropunctata) (Signoret). Utilizing an O-antigen mutant, which produces a truncated LPS molecule, results showed that structural alterations to the O-antigen cause a change in the physiochemical properties of the cell surface. Moreover, these alterations significantly affect attachment of X. fastidiosa to an insect cuticular substrate and to insect foreguts. Scanning electron microscopy confirmed that this defect in initial attachment prevents biofilm formation within vector foreguts, impairing pathogen acquisition. These results demonstrate that, in addition to reported protein adhesin-ligand interactions, LPS contributes to the pathogen-vector interaction during transmission of this destructive agricultural pathogen.