Quorum sensing and virulence regulation inXanthomonas campestris

Abstract

It is now clear that cell-cell communication, often referred to as quorum sensing (QS), is the norm in the prokaryotic kingdom and this community-wide genetic regulatory mechanism has been adopted for regulation of many important biological functions. Since the 1980s, several types of QS signals have been identified, which are associated commonly with different types of QS mechanisms. Among them, the diffusible signal factor (DSF)-dependent QS system, originally discovered from bacterial pathogen Xanthomonas campestris pv. campestris, is a relatively new regulatory mechanism. The rapid research progress over the last few years has identified the chemical structure of the QS signal DSF, established the DSF regulon, and unveiled the general signaling pathways and mechanisms. Particular noteworthy are that DSF biosynthesis is modulated by a novel posttranslational autoinduction mechanism involving protein-protein interaction between the DSF synthase RpfF and the sensor RpfC, and that QS signal sensing is coupled to intracellular regulatory networks through a second messenger cyclic-di-GMP and a global regulator Clp. Genomic and genetic analyses show that the DSF QS-signaling pathway regulates diverse biological functions including virulence, biofilm dispersal, and ecological competence. Moreover, evidence is emerging that the DSF QS system is conserved in a range of plant and human bacterial pathogens.

Biosynthesis of the immunosuppressants FK506, FK520, and rapamycin involves a previously undescribed family of enzymes acting on chorismate

“…Deletion of the gene for the FkbO/RapK-like protein abolishes both pigment production and extracellular polysaccharide production dependent on a diffusible factor (47). Because these authors had relied on early annotation of FkbO/RapK-like proteins as pteridine-dependent dioxygenases, the recognition of these proteins as potential 3HBA synthases should lead to a useful reevaluation of their role in Xanthomonas and related phytopathogenic bacteria (48).…”

The RpfCG two-component system negatively regulates the colonization of sugar cane stalks by Xanthomonas albilineans

“…Phenotypes due to mutation in different rpf genes vary according to the bacterial pathogen, from deficiency in virulence to hypervirulence, thus suggesting that members of the Xanthomonadaceae family have adapted their signalling system to fit specific needs for colonization of different hosts (Dow, 2008). In Xanthomonas species, mutation of rpfF or rpfC results in reduction of virulence (Dow et al, 2003;He & Zhang, 2008;Siciliano et al, 2006;Thowthampitak et al, 2008). In contrast, in Xylella fastidiosa, rpfF mutants are more virulent than the wildtype strain when mechanically inoculated into plants (Newman et al, 2004).…”

“…In Xanthomonas species and Xylella fastidiosa, biofilm formation is essential for virulence and is controlled by DSF (Chatterjee et al, 2010;Dow, 2008;Dow et al, 2003;He & Zhang, 2008;Ryan & Dow, 2011;Torres et al, 2007). However, microscopic observations of rpf mutants of Xanthomonas albilineans in inoculated plants showed that these mutants were still able to form bacterial aggregates in xylem vessels (I. Mensi, unpublished data), suggesting that DSF does not control biofilm formation in this pathogen.…”

“…The rpfF gene has been shown to be required for production of DSF (Barber et al, 1997;Newman et al, 2004), which is a cis-unsaturated fatty acid (Wang et al, 2004). Perception of DSF and signal transduction depends on a two-component signal transduction system that comprises the sensor kinase RpfC and the regulator RpfG (He & Zhang, 2008;Ryan & Dow, 2011;Ryan et al, 2012). The sensor RpfC is known to negatively regulate the synthesis of DSF, and mutation of rpfC results in overproduction of DSF.…”

“…This cluster of genes encodes a quorum sensing (also called cell-cell signalling) system that controls several cellular and biological processes in Xylella fastidiosa, Stenotrophomonas maltophilia and several species of Xanthomonas (Barber et al, 1997;Chatterjee et al, 2008b;Dow, 2008;Fouhy et al, 2007;He & Zhang, 2008;Tang et al, 1991). The rpf gene cluster is especially used by these pathogenic bacteria to regulate the expression of factors contributing to virulence, such as extracellular polysaccharides, extracellular enzymes and flagellum synthesis (Dow et al, 2003;Guo et al, 2012;He et al, 2006;Ryan & Dow, 2011;Wang et al, 2012).…”