Upstream Migration ofXylella fastidiosavia Pilus-Driven Twitching Motility

Abstract

Xylella fastidiosa is a xylem-limited nonflagellated bacterium that causes economically important diseases of plants by developing biofilms that block xylem sap flow. How the bacterium is translocated downward in the host plant's vascular system against the direction of the transpiration stream has long been a puzzling phenomenon. Using microfabricated chambers designed to mimic some of the features of xylem vessels, we discovered that X. fastidiosa migrates via type IV-pilus-mediated twitching motility at speeds up to 5 m min ؊1 against a rapidly flowing medium (20,000 m min ؊1 ). Electron microscopy revealed that there are two length classes of pili, long type IV pili (1.0 to 5.8 m) and short type I pili (0.4 to 1.0 m). We further demonstrated that two knockout mutants (pilB and pilQ mutants) that are deficient in type IV pili do not twitch and are inhibited from colonizing upstream vascular regions in planta. In addition, mutants with insertions in pilB or pilQ (possessing type I pili only) express enhanced biofilm formation, whereas a mutant with an insertion in fimA (possessing only type IV pili) is biofilm deficient.

Biological and genetic factors regulating natural competence in a bacterial plant pathogen

“…Thus, DNA transport from the extracellular environment into the cytoplasm in X. fastidiosa likely occurs in a similar fashion to what has been observed in other bacteria, requiring a type IV pilus or like structure and a series of Com proteins (Busch et al, 1999;Chen & Dubnau, 2004;Hamilton & Dillard, 2006;Meibom et al, 2005;Meier et al, 2002). While many of the pil genes in X. fastidiosa are grouped together in several operons (Li et al, 2007;Meng et al, 2005), the com genes tested here do not appear to be in operons with other competence-related genes.…”

“…0.35 % of wildtype for the pilB mutant) or transformation was undetectable (pilO and pilQ mutants). Previous work has shown that these three pil mutants do not produce any type IV pili (Li et al, 2007;Meng et al, 2005). As the PilB, PilO and PilQ proteins in X. fastidiosa are likely required for pilus assembly and retraction, a mutation in any of the genes encoding these proteins is much more likely to lead to non-functional pili compared to a mutation in pilY1.…”

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…While X. fastidiosa is a non-flagellating bacterium, it harbors several genes that encode proteins involved in production and function of type IV pili (Simpson et al 2000;van Sluys et al 2003). These long, polar located pili have been shown to be involved in twitching motility in X. fastidiosa (Meng et al 2005). Intriguingly, such twitching motility was demonstrated to enable the movement of X. fastidiosa not only along abiotic surfaces, but also along xylem vessels.…”

“…Intriguingly, such twitching motility was demonstrated to enable the movement of X. fastidiosa not only along abiotic surfaces, but also along xylem vessels. Importantly, X. fastidiosa exhibits the ability to actively move against the flow of xylem fluids in vessels by twitching motility (Meng et al 2005). The apparently high efficiency with which cells of X. fastidiosa move through the orifices of pits (Newman et al 2004), which are apparently enlarged due to the action of extracellular enzymes secreted by this pathogen (Perez-Donoso et al 2010), may be due at least in part to its ability to move along surfaces by retraction of the type IV pili.…”

Bacterial rheotaxis

“…Responses to shear are also observed in copepods and dinoflagellates, which rely on shear detection to attack prey or escape predators (5,(17)(18)(19), orient in flow (20), and retain a preferential depth (21). Evidence of shear-driven motility in prokaryotes is limited to the upstream motion of mycoplasma (22), E. coli (23), and Xylella fastidiosa (24), all of which require the presence of a solid surface. In contrast, little is known about the effect of shear on bacteria freely swimming in the bulk fluid.…”