Decoding the genetic and functional diversity of the DSF quorum-sensing system in Stenotrophomonas maltophilia

Abstract

Stenotrophomonas maltophilia uses the Diffusible Signal Factor (DSF) quorum sensing (QS) system to mediate intra- and inter-specific signaling and regulate virulence-related processes. The components of this system are encoded by the rpf cluster, with genes rpfF and rpfC encoding for the DSF synthase RpfF and sensor RpfC, respectively. Recently, we have shown that there exist two variants of the rpf cluster (rpf-1 and rpf-2), distinguishing two groups of S. maltophilia strains. Surprisingly, only rpf-1 strains produce detectable DSF, correlating with their ability to control biofilm formation, swarming motility and virulence. The evolutive advantage of acquiring two different rpf clusters, the phylogenetic time point and mechanism of this acquisition and the conditions that activate DSF production in rpf-2 strains, are however not known. Examination of this cluster in various species suggests that its variability originated most probably by genetic exchange between rhizosphere bacteria. We propose that rpf-2 variant strains make use of a strategy recently termed as “social cheating.” Analysis of cellular and extracellular fatty acids (FAs) of strains E77 (rpf-1) and M30 (rpf-2) suggests that their RpfFs have also a thioesterase activity that facilitates the release of unspecific FAs to the medium in addition to DSF. Production of DSF in rpf-1 strains appears in fact to be modulated by some of these extracellular FAs in addition to other factors such as temperature and nutrients, while in rpf-2 strains DSF biosynthesis is derepressed only upon detection of DSF itself, suggesting that they require cohabitation with DSF-producer bacteria to activate their DSF regulatory machinery. Finally, we show that the mixed rpf-1/rpf-2 population presents synergism in DSF production and virulence capacity in an in vivo infection model. Recovery and quantification of DSF from co-infected animals correlates with the observed mortality rate.

Diffusible Signal Factor signaling regulates multiple functions in the opportunistic pathogen Stenotrophomonas maltophilia

“…These findings suggest that DSF signaling contributes to the virulence of S. maltophilia . The pleiotropic effects of loss by mutation rpfF are consistent with previous observations in different strains of S. maltophilia and species of Stentotrophomonas such as S. rhizophila , where rpfF mutants have altered biofilm formation, extracellular polysaccharide synthesis and virulence (Alvai et al, 2013; Huedo et al, 2015).…”

“…Our findings thus add to a body of work that indicates a role for cell-cell signaling in the virulence of diverse bacterial pathogens. Furthermore, the work is consistent with recent studies that identify the importance of RpfF proteins and DSF signaling in regulation in other environmental strains of S. maltophilia (Alvai et al, 2013; Huedo et al, 2015). Interference with such signaling processes affords a rational approach to aid the treatment of bacterial infections (Ryan et al, 2015).…”

“…Isolates are resistant to the majority of clinically useful antibiotics making the treatment of S. maltophilia infections problematic (Crossman et al, 2008). A number of laboratories have been addressing the molecular bases for virulence and antibiotic resistance in S. maltophilia (Ryan et al, 2009; Alvai et al, 2013; Huedo et al, 2015; Berg and Martinez, 2015; An and Berg, 2018).…”

Stenotrophomonas maltophilia Phenotypic and Genotypic Diversity during a 10-year Colonization in the Lungs of a Cystic Fibrosis Patient

“…These determinants are unique in context of this pathogen's limited virulence that limits its invasive potential in comparison to other evolved pathogens like P. aeruginosa . However, S. maltophilia is increasingly known to employ multifactorial determinants like extracellular proteases (Karaba et al, 2013 ), host cell actin modifiers (MacDonald et al, 2016 ), quorum signaling molecules (Huedo et al, 2015 ), and highly evolved efflux-pumps (Chang et al, 2015 ), which independently or together offer formidable recalcitrance and pathogenic fitness.…”

Systematic Mutational Analysis of Histidine Kinase Genes in the Nosocomial Pathogen Stenotrophomonas maltophilia Identifies BfmAK System Control of Biofilm Development

“…However, TCS regulation, one of the central molecular mechanisms potentially targetable by novel antibacterial agents, lacks proper investigation in S. maltophilia. Indeed, only HK RpfC, which is responsible for regulating cell-cell communication and virulence factor expression in the close-relative bacteria Xanthomonas spp., has been shown to control diffusible signaling factor (DSF)-triggered modulation in S. maltophilia (14)(15)(16). Our previous study identified FsnR, an orphan RR that controls transcription of flagellar genes and biofilm formation (17), but the cognate HK for FsnR remains unclear.…”