Ralstonia solanacearum requires type 4 pili to adhere to multiple surfaces and for natural transformation and virulence

Abstract

SummaryAs reported previously for Ralstonia solanacearum strain GMI1000, wild-type strains AW1 and K60 were shown to produce Hrp pili. AW1 and K60 mutants lacking Hrp pili still exhibited twitching motility, which requires type 4 pili (Tfp), and electron microscopy revealed that they still made flexuous polar pili. Twitching-positive cells had an extracellular 17 kDa protein that was associated with piliation, and an internal 43-amino-acid sequence of this protein was typical of type 4 pilins. This amino acid sequence is encoded by an open reading frame, designated pilA , in the genomic sequence of GMI1000. PilA is 46% identical to a Pseudomonas aeruginosa type 4 pilin over its entire length and has all the conserved residues and motifs characteristic of type 4 group A pilins. pilA mutants did not make the 17 kDa PilA protein and did not exhibit twitching motility. When compared with its parent, an AW1 pilA mutant was reduced in virulence on tomato plants and in autoaggregation and biofilm formation in broth culture. Unlike AW1, a pilA mutant did not exhibit polar attachment to tobacco suspension culture cells or to tomato roots; it was also not naturally competent for transformation. We reported previously that twitching motility ceases in maturing AW1 colonies and that inactivation of PhcA, a global transcriptional regulator, results in colonies that continue to exhibit twitching motility. Similarly, in broth culture, expression of a pilA :: lacZ fusion in AW1 decreased 10-fold at high cell density, but expression remained high in a phcA mutant. In addition, pilA :: lacZ expression was positively regulated 10-fold by PehR, a response regulator that is known to be repressed by PhcA. This signal cascade is sufficient to explain why pilA expression, and thus twitching motility, decreases at high cell densities.

Ralstonia solanacearum RSc0411 (lptC) is a determinant for full virulence and has a strain-specific novel function in the T3SS activity

“…S3b) implies that lowered LPS level does not affect the mutant's survival inside host plants at the initial stage. In addition, the reduced biofilm formation and root attachment are expected to cause reduced bacterial sustainability outside and inside the plants (Kang et al, 2002), and the impaired swimming activity would affect bacterial virulence (TansKersten et al, 2001(TansKersten et al, , 2004. All of the defects taken together lead to reduced suitability of R. solanacearum mutants during systemic infection and thus attenuated virulence on host plants.…”

Characterization of Xylella fastidiosa popP Gene Required for Pathogenicitya

“…Biofilms are complex structures involving X. fastidiosa cells and an extracellular matrix. X. fastidiosa produces abundant multiple putative afimbrial adhesins, such as exopolysaccharide (EPS), lipopolysaccharide (LPS), and surface proteins, which contribute to the virulence of X. fastidiosa by attaching to the xylem wall in the plant and enhancing biofilm formation [33,[40][41][42][43]. Previously study showed that X. fastidiosa EPS was coded by a cluster of nine gum genes closely related to the xanthan gum operon of Xanthomonas campestris pv.…”

Tomato as a model plant for plant-pathogen interactions

“…From AAL, a cluster of the genes responsible for biosynthesis of AALtoxin has been identified (Yamagishi et al 2006). R. solanacearum has as many as 35 genes homologous to type IV pili genes, which may be involved in cell-to-cell aggregation (Kang et al 2002).…”