Genome scale analysis of diffusible signal factor regulon in Xanthomonas campestris pv. campestris: identification of novel cell–cell communication‐dependent genes and functions

Abstract

SummaryThe bacterial pathogen Xanthomonas campestris pv. campestris ( Xcc ) recruits a diffusible signal factor (DSF), which has recently been structurally characterized as cis -11-methyl-2-dodecenoic acid, as a cellcell communication signal to synchronize virulence gene expression and biofilm dispersal. In this study, we showed that despite the existance of phenotype variations in different Xcc isolates, the DSF-mediated functions were in general conserved. To investigate the genomic profiles of DSF regulation, we designed and conducted oligomicroarray analysis by comparison of the gene expression patterns of wild-type strain XC1 and its DSF-deficient mutant XC1dF, as well as those of XC1dF in the presence or absence of DSF signals. The analyses led to identification of 165 genes, whose expression was significantly influenced by DSF signals. These genes encode proteins and enzymes belonging to at least 12 functional groups. In addition to those previously known DSF-dependent activities such as production of extracellular enzymes and extracellular polysaccharides, microarray analyses also revealed new functions mediated by DSF, such as flagellum synthesis, resistance to toxins and oxidative stress, and aerobic respiration. Phenotype analyses confirmed that DSF signalling contributed to resistance to toxin acriflavin and hydrogen peroxide, and to the survival of bacterial cells at different temperatures. We conclude that DSF cell-cell signalling is not only essential for co-ordinating the expression of virulence genes but also plays a vital role in keeping up the general competence of the pathogen in ecosystems.

Cell–cell signal-dependent dynamic interactions between HD-GYP and GGDEF domain proteins mediate virulence in Xanthomonas campestris

“…It is interesting in this context that DSF signaling has been shown to activate transcription of the gene encoding the cyclic-AMP receptor-like protein Clp (22), although the mechanism remains obscure. In Xcc, Clp regulates many functions, including the expression of genes encoding extracellular enzymes, but apparently is not involved in the regulation of biofilm dynamics (22,23). Intriguingly, recent findings have indicated that the promoter-binding activity of Clp is influenced negatively by cyclic di-GMP (24).…”

Regulation of the pehA gene encoding the major polygalacturonase of Xanthomonas campestris by Clp and RpfF

“…So far, only two extracellular enzyme genes (engA and prt1) have been demonstrated to be affected by a rpfA mutation (Wilson et al, 1998). Although details of regulatory circuits remain to be elucidated, recent microarray analyses have identified 165 Xcc genes that are regulated by RpfF/DSF (He et al, 2006).…”

“…These extracellular products have long been considered important virulence determinants (Chan & Goodwin, 1999;Chang et al, 2001;Chou et al, 1997;Dow et al, 1987;Dums et al, 1991;Soby & Daniels, 1996;Yang & Tseng, 1988). Production of these determinants is regulated by the global transcription factor Clp (cAMP receptor protein-like protein) and the rpf (regulator of pathogenicity factors) gene cluster (Barber et al, 1997;de Crecy-Lagard et al, 1990;Dow et al, 2000;He et al, 2006He et al, , 2007Tang et al, 1991;Tseng et al, 1999;Wilson et al, 1998).…”

Mutation of the gene encoding a major outer-membrane protein in Xanthomonas campestris pv. campestris causes pleiotropic effects, including loss of pathogenicity

“…As the cell surface is greatly deformed, the mopB mutation may have drastically changed the topology of GumB; without proper positioning of this important protein, the xanthan export machinery will malfunction. It is known that xanthan production is upregulated by DSF and Clp (He et al, 2006(He et al, , 2007Slater et al, 2000), but little is known about the roles of other possible regulators. In E. coli K1, expression of type 1 fimbriae, controlled by phase variation, is decreased upon deletion of ompA (Teng et al, 2006).…”