Understanding control of Xf cell aggregation: Importance in colonization and biofilm development in grapevine and sharpshooter foregut

PIs: Thomas Burr, Harvey Hoch

• Progress report submitted on March 10, 2008

Research Papers

• Mutations in type I and type IV pilus biosynthetic genes affect twitching motility rates in Xylella fastidiosa
  Xylellafastidiosa possesses both type I and type IV pilli at the same cell pole. By use of a microfluidic device, the speed of twitching movement by wild-type cells on a glass surface against the How direction of media was measured as 0.86 (standard error [SE1, 0.04) mu m min(-1). A type I pilus mutant (fimA) moved six times faster (4.85 [SE, 0.27] mu m min(-1)) and a pilY1 mutant moved three times slower (0.28 [SE, 0.031 mu m min(-1)) than wild-type cells. Type I pili slow the rate movement, while the putative type IV pilus protein PilY1 is likely important for attachment to surfaces.
  Oct. 1, 2007
  
• Assessing adhesion forces of type I and type IV pili of Xylella fastidiosa bacteria by use of a microfluidic flow chamber
  Xylella fastidiosa, a bacterium responsible for Pierce's disease in grapevines, possesses both type I and type IV pili at the same cell pole. Type IV pili facilitate twitching motility, and type I pili are involved in biofilm development. The adhesiveness of the bacteria and the roles of the two pili types in attachment to a glass substratum were evaluated using a microfluidic flow chamber in conjunction with pilus-defective mutants. The average adhesion force necessary to detach wild-type X. fastidiosa cells was 147 +/- 11 pN. Mutant cells possessing only type I pili required a force of 204 +/- 22 pN for removal, whereas cells possessing only type IV pili required 119 +/- 8 pN to dislodge these cells. The experimental results demonstrate that microfluidic flow chambers are useful and convenient tools for assessing the drag forces necessary for detaching bacterial cells and that with specific pilus mutants, the role of the pilus type can be further assessed.
  April 1, 2007
  
• Twitching motility among pathogenic Xylella fastidiosa isolates and the influence of bovine serum albumin on twitching-dependent colony fringe morphology
  Fourteen Xylella fastidiosa isolates from grapevines exhibiting Pierce's disease symptoms in California, Texas, and South Carolina were examined for type IV pilus-mediated twitching motility, a phenotype previously observed in a Temecula isolate from California. All isolates except one from South Carolina (SC 19A97) exhibited colonies with a peripheral fringe on PW agar, a feature indicative of twitching motility; however, when individual cells of SC 19A97 were examined at higher magnifications twitching motility was observed. The presence and width of colony peripheral fringes were related to the amount of bovine serum albumin (BSA) present in the medium; no or low levels of BSA (0-1.8 g L-1) permitted development of the widest fringe, whereas higher levels (3.5-6.0 g L-1) severely limited, and in many instances prevented, peripheral fringe development. The growth rate of the wild-type Temecula isolate in PW broth with different concentrations of BSA was similar for all tested concentrations of BSA; however, growth was significantly reduced in medium without BSA.
  March 1, 2007
  

Funding sources:

• Funded by: UC PD Fund
• Budget: $218,850.00
• Start date: July 15, 2006
• Stop date: July 14, 2008
• Status: APPROVED