Twitching motility of Ralstonia solanacearum requires a type IV pilus system

Abstract

Twitching motility is a form of bacterial translocation over firm surfaces that requires retractile type IV pili. Microscopic colonies of Ralstonia solanacearum strains AW1, K60 and GMI1000 growing on the surface of a rich medium solidified with 16 % agar appeared to exhibit twitching motility, because early on they divided into motile ' rafts ' of cells and later developed protruding ' spearheads ' at their margins. Individual motile bacteria were observed only when they were embedded within masses of other cells. Varying degrees of motility were observed for 33 of 35 strains of R. solanacearum in a selected, diverse collection. Timing was more important than culture conditions for observing motility, because by the time wild-type colonies were easily visible by eye (about 48 h) this activity ceased and the spearheads were obscured by continued bacterial multiplication. In contrast, inactivation of PhcA, a transcriptional regulator that is essential for R. solanacearum to cause plant disease, resulted in colonies that continued to expand for at least several additional days. Multiple strains with mutations in regulatory genes important for virulence were tested, but all exhibited wild-type motility. Many of the genes required for production of functional type IV pili, and hence for twitching motility, are conserved among unrelated bacteria, and pilD, pilQ and pilT orthologues were identified in R. solanacearum. Colonies of R. solanacearum pilQ and pilT mutants did not develop spearheads or rafts, confirming that the movement of cells that had been observed was due to twitching motility. Compared to the wild-type parents, both pilQ and pilT mutants caused slower and less severe wilting on susceptible tomato plants. This is the first report of twitching motility by a phytopathogenic bacterium, and the first example where type IV pili appear to contribute significantly to plant pathogenesis.

Coupling Factors in Macromolecular Type-IV Secretion Machineries

“…They bear Walker A (motif I) and B (motif II or DExx box) NTP-binding sequences [88] and may use the energy of Rhizobium etli bacterium; N2-fixation [154] Sinorhizobium meliloti bacterium; N2-fixation [14,15,17] Shigella flexneri plasmid ColIb P9 bacterium; diarrhoea / dysentery [155] Bartonella henselae and tribocorum bacterium; cat scratch disease, bacteremia [156][157][158][159][160] Campylobacter jejuni bacterium; bacterial diarrhoea [161,162] Toxoplasma gondii protozoon; toxoplasmosis (encephalitis) [54] Leishmania donovani protozoon; leishmaniasis [54] Mycobacterium tuberculosis bacterium; tuberculosis [54] Bordetella bronchiseptica bacterium; bronchitis [14,15,17] Enterobacter aerogenes bacterium; nosocomial infections [11] Actinobacillus actinomycetemcomitans bacterium; periodontitis [14,15,17,163,164] Escherichia coli bacterium; diarrhea [11] Caulobacter crescentus bacterium; non-pathogenic [14,15,17] Coxiella burnetii bacterium; acute febrile disease, endocarditis, pneumonitis [165,166] Thiobacillus ferroxidans bacterium; iron oxidation [14,15,17] Wolbachia intracellular symbiont of arthropods; sexual alterations in host [167,168] Ralstonia eutrophantus bacterium; heavy-metal resistance [11,169] Salmonella typhi, typhimurium and enteriditis bacterium; typhus, salmonellosis …”

Type I and type IV pili of Xylella fastidiosa affect twitching motility, biofilm formation and cell–cell aggregation

“…It has been observed mostly in saprophytic bacteria and mammalian pathogens. Such motility in plant-associated bacteria has been observed in Ralstonia solanacearum (Kang et al, 2002;Liu et al, 2001) and X. fastidiosa (Meng et al, 2005). To date, approximately 40 genes have been identified that are involved in the biogenesis and function of type IV pili in Pseudomonas aeruginosa (Mattick, 2002), including the genes that encode the major structural protein (PilA), and those that encode the minor proteins involved in formation of the base and/or tip of the pilus, e.g.…”

Elucidation of the Regulon and cis -Acting Regulatory Element of HrpB, the AraC-Type Regulator of a Plant Pathogen-Like Type III Secretion System in Burkholderia pseudomallei

“…However, soaking plantlets in suspensions of nonphytopathogenic P. putida ATCC 12633 or media alone also caused wilting. Moreover, we found that after 36 A hallmark of nearly all plant-pathogenic bacteria is the ability to produce a hypersensitive response in tobacco (13,23,79). Tobacco leaves infiltrated with 10 9 cells ml Ϫ1 of B. thailandensis or P. putida did not elicit a hypersensitive response after 7 days, while those infiltrated with the same amount of R. solanacearum developed a hypersensitive response after 2 days.…”

“…Escherichia coli, B. pseudomallei, and B. thailandensis were grown at 37°C in Luria-Bertani medium (LB) (42), LB supplemented with 2% glycerol (LBG), or M9 medium (57) with 20 mM glutamate instead of glucose. R. solanacearum and Pseudomonas putida were grown at 30°C in 1% Bacto peptone, 0.1% Casamino Acids, 0.1% yeast extract, and 0.5% glucose (BG) (36). When necessary, antibiotics were used at the following concentrations: kanamycin at 50 g/ml (Km 50 ) for Burkholderia spp.…”