Abstracts Biological Sciences

Novel Virulent Phages for Xylella fastidiosa and Other Members of the Xanthomonadaceae

by Stephen J Ahern

The xylem-limited bacterium, Xylella fastidiosa, is the causal agent of several plant diseases, most notably Pierce?s Disease of grapes and citrus variegated chlorosis. We report on the isolation and characterization of the first virulent phages for X. fastidiosa, Xfas103, Xfas106, Xfas303, Xfas304, with host ranges extending to Xanthomonas. Efficiency of plating on X. fastidiosa strain Temecula or Xanthomonas strain EC-12 ranged from 1.41 x 10^(-1) to 2.29 x 10^(-3) , depending on propagating and plating host. Phages propagated on homologous hosts had an observed adsorption rate constant of (4.33 ? 0.28) x 10^(-12) ml cell^(-1) min^(-1) for strain Temecula, and ranged from (4.58 ? 0.30) x 10^(-10) to (7.26 ? 0.42) x 10^(-10) ml cell^(-1) min^(-1) for strain EC-12. Siphophages Xfas103 and Xfas106 exhibit over 80% nucleotide identity to each other and are syntenic to phage BcepNazgul. Here it is proposed that phage BcepNazgul is the founding member of a novel phage type, to which Xfas103 and Xfas106 belong. Podophages Xfas303 and Xfas304 show no significant DNA homology, both encode for a single subunit RNA polymerase at the right end of the class II gene cluster, and are new members of the phiKMV-like phage type. The four phages utilize Type IV pili as receptors to infect strains Temecula and EC-12. The phages may be useful as agents for an effective and environmentally friendly strategy for the control of diseases caused by X. fastidiosa.