Role of type IV pili in biofilm formation and virulence of Xylophilus ampelinus
Yolanda Petersen: Agricultural Research Council
<div>Grapevine bacterial blight and necrosis caused by the bacterium<em> Xylophilus ampelinus</em>, has been a problem in South African vineyards for many decades. The disease reduces productivity and shortens the lifespan of infected vines. Although type IV pili (T4P) have been shown to be important in attachment, motility and biofilm formation for several plant and animal pathogens, this has not yet been explored for <em>X. ampelinus</em>. Therefore, we undertook a preliminary study to evaluate the importance of <em>X. ampelinus</em> T4P in virulence on grapevine. The study was conducted utilizing two mutants from a transposon mutant library with insertions in the genes, <em>pilY1</em> and <em>pilQ</em>. The presence of a single <em>pilY1</em> homolog in the <em>X. ampelinus</em> genome was confirmed. <em>In vitro </em>biofilm formation on glass surfaces as well as twitching motility on 1% agar plates was impaired in both mutants. Assessment of virulence susceptible grapevine cultivar, Redglobe, showed that although the rate of symptom development and disease severity for the <em>pilQ</em> mutant was comparable to the wild type, plants inoculated with the <em>pilY1</em> mutant developed symptoms faster than the wild type. However, symptom expression three months post-inoculation was comparable to the wild type. Both mutants were able to migrate up- and downstream from the point of inoculation on the shoots. Results from the <em>in vitro</em> assays confirmed the role of T4P in biofilm formation on abiotic surfaces and twitching motility. The <em>in planta</em> results, however, are contrary to those for vascular plant pathogens <em>Xylella fastidiosa</em> and <em>Acidovorax citrulli</em>. Further examination of the role of T4P in the <em>in planta</em> biofilm formation is currently under way.</div>
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