Biofilm dispersal inXanthomonas campestrisis controlled by cell–cell signaling and is required for full virulence to plants

Abstract

The rpf gene cluster of Xanthomonas campestris pathovar campestris (Xcc) is required for the pathogenesis of this bacterium to plants. Several rpf genes are involved in the coordinate positive regulation of the production of virulence factors mediated by the small diffusible molecule DSF (for diffusible signal factor). RpfF directs the synthesis of DSF, and a two-component sensory transduction system comprising RpfC and RpfG has been implicated in the perception of the DSF signal and signal transduction. In L medium, rpfF, rpfG, rpfC, and rpfGHC mutants grew as matrixenclosed aggregates, whereas the wild type grew in a dispersed planktonic fashion. Synthesis of the extracellular polysaccharide xanthan was required for aggregate formation. Addition of DSF triggered dispersion of the aggregates formed by the rpfF strain, but not those of rpf strains defective in DSF signal transduction. An extracellular enzyme from Xcc whose synthesis was positively controlled by the DSF͞rpf system could disperse the aggregates produced by all rpf strains. The enzyme was identified as the single endo-␤-1,4-mannanase encoded by the Xcc genome. This enzyme had no detectable activity against soluble xanthan. The endo-␤-1,4-mannanase was required for the full virulence of Xcc to plants. On the basis of this model system, we propose that one role of the ␤-mannanase during disease is to promote transitions from an aggregated or biofilm lifestyle to a planktonic lifestyle in response to the DSF signal.

Sticky Situations: Key Components That Control Bacterial Surface Attachment

“…The fatty acid messenger cis-2-decenoic acid (CDA) has recently been described to play a role in self-induced dispersion by P. aeruginosa biofilms (34). This molecule is functionally and structurally related to the class of short-chain fatty acid signaling molecules that includes the diffusible signal factor DSF, which acts as a cell-to-cell communication molecule in Xanthomonas campestris (41). Active at nanomolar concentrations, CDA was demonstrated to also induce dispersion of biofilms formed by a variety of Gram-negative and -positive bacteria as well as by Candida albicans.…”

Genomic Insights into Xylella fastidiosa Interactions with Plant and Insect Hosts

“…In Xanthomonas ssp. and X. fastidiosa, rpf controls synthesis and detection of DSF, a medium-chain fatty acid that functions as a signaling molecule (Colnaghi Simionato et al 2007;Dow et al 2003). The rpf cluster in Xanthomonas ssp.…”

“…While rpfC is not impaired in attachment to vector foreguts, transmission is reduced due to increased adhesin expression and lower rates of cell detachment (Chatterjee et al 2008b). In X. campestris, DSF regulates the production of an enzyme that controls cell dispersal from a biofilm (Dow et al 2003). The inability of rpfC to detach from the biofilm in the insect foregut implicates DSF signaling as an important but uncharacterized regulator of expression controlling cell detachment from biofilm bound cells in the insect foregut.…”

Glyceraldehyde-3-phosphate dehydrogenase of Xanthomonas campestris pv. campestris is required for extracellular polysaccharide production and full virulence

“…The virulence of Xcc to the host plant Chinese radish (Raphanus sativus) was tested by the leaf-clipping method (Dow et al, 2003). Lesion length was measured 10 days after inoculation and data were analysed by t-test.…”

“…To determine whether GAPDH is involved in the pathogenicity of Xcc, the virulence of the GAPDH-deficient mutant 0972nk was tested on the host plant Chinese radish by the leaf-clipping method (Dow et al, 2003). Ten days after inoculation, the mutant caused black-rot symptoms with a mean lesion length of 5.5 mm, whereas the wildtype produced a mean lesion length of about 12 mm (Fig.…”