Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2008
Publication Date: 11/20/2008
Citation: Cheng, D.W., Lin, H., Walker, A., Stenger, D.C., Civerolo, E.L. 2008. Effects of Grape Xylem Sap and Cell-Wall Constituents on In Vitro Growth, Biofilm Formation and Cellular Aggregation of Xylella fastidiosa. Proceedings of the CDFA Pierce's Disease Control Program Research Symposium, December 15-17, 2008, San Diego, California. pp.118-122. Interpretive Summary: Effects of xylem sap from grapes or purified cell wall constituents on in vitro growth, biofilm formation, cell aggregation, and gene expression of Xylella fastidiosa (causal agent of Pierce’s disease [PD]) were determined. Media containing xylem sap from PD-susceptible grapevines provided better support for bacterial growth and biofilm formation than the media supplemented with xylem sap from PD-resistant plants. Culturing X. fastidiosa on media containing various purified cell-wall constituents demonstrated that some cell wall constituents enhanced bacterial growth whereas others strongly suppressed growth. These compounds also affected bacterial cell aggregation under in vitro culture conditions. Expression of X. fastidiosa genes encoding cell wall digestion enzymes (endoglucanase, endo-1,4-beta-glucanase, and periplasm protease) was differentially regulated in response to amendment of medium with xylem sap from PD-resistant and PD-susceptible grapevines. Differential effects on X. fastidiosa growth, biofilm formation, cellular aggregation, and gene expression suggests that xylem sap composition and cell wall properties among PD-resistant and PD-susceptible grapes may influence disease development of grapevines infected with X. fastidosa.
Technical Abstract: Purified cell-wall constituents or grape xylem sap added to media affected in vitro growth, biofilm formation, cell aggregation and gene expression of Xylella fastidiosa. Media containing xylem sap from Pierce’s disease (PD)-susceptible plants provided better support for bacterial growth and biofilm formation than media supplemented with xylem sap from PD-resistant plants. Culturing X. fastidiosa on media containing various purified cell-wall constituents demonstrated that CM-cellulose, xylan, ß-D-glucan, k-carrageenan, cello-oligosaccharide and laminarin promoted bacterial growth whereas lichenan strongly suppressed growth. However, only laminarin, xylan, and k-carrageenan promoted biofilm formation in vitro. Lichenan, oligosaccharide, k-carrageenan, laminarin, xylan and ß-D-glucan all significantly decreased bacterial cell aggregation in vitro. Quantitative real-time PCR assays revealed that expression of genes encoding extracellular endoglucanase, endo-1,4-beta-glucanase, and periplasm protease were differentially regulated in response to amendment of media with xylem sap from PD- resistant and PD- susceptible grapevines. This study indicates that composition of xylem sap and cell walls influence basic parameters of X. fastidiosa biology which may, in turn, account for differences in pathogenesis of X. fastidiosa on PD-resistant and –susceptible grapevines.