Draft Genome Sequence of Stenotrophomonas maltophilia Strain M30, Isolated from a Chronic Pressure Ulcer in an Elderly Patient

Quorum Sensing Signaling and Quenching in the Multidrug-Resistant Pathogen Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic Gram-negative pathogen with increasing incidence in clinical settings. The most critical aspect of S. maltophilia is its frequent resistance to a majority of the antibiotics of clinical use. Quorum Sensing (QS) systems coordinate bacterial populations and act as major regulatory mechanisms of pathogenesis in both pure cultures and poly-microbial communities. Disruption of QS systems, a phenomenon known as Quorum Quenching (QQ), represents a new promising paradigm for the design of novel antimicrobial strategies. In this context, we review the main advances in the field of QS in S. maltophilia by paying special attention to Diffusible Signal Factor (DSF) signaling, Acyl Homoserine Lactone (AHL) responses and the controversial Ax21 system. Advances in the DSF system include regulatory aspects of DSF synthesis and perception by both rpf-1 and rpf-2 variant systems, as well as their reciprocal communication. Interaction via DSF of S. maltophilia with unrelated organisms including bacteria, yeast and plants is also considered. Finally, an overview of the different QQ mechanisms involving S. maltophilia as quencher and as object of quenching is presented, revealing the potential of this species for use in QQ applications. This review provides a comprehensive snapshot of the interconnected QS network that S. maltophilia uses to sense and respond to its surrounding biotic or abiotic environment. Understanding such cooperative and competitive communication mechanisms is essential for the design of effective anti QS strategies.

Proteomic analysis of outer membrane proteins and vesicles of a clinical isolate and a collection strain of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a Gram-negative pathogen with emerging nosocomial incidence that displays a high genomic diversity, complicating the study of its pathogenicity, virulence and resistance factors. The interaction of bacterial pathogens with host cells is largely mediated by outer membrane proteins (OMPs). Indeed, several OMPs of Gram-negative bacteria have been recognized as important virulence factors and targets for host immune recognition or to be involved in mechanisms of resistance to antimicrobials. OMPs are also present in outer membrane vesicles (OMVs), which bacteria constitutively secrete to the extracellular milieu and are essential for bacterial survival and pathogenesis. Here, we report the characterization of the OMP and native OMV subproteomes of a clinical isolate (M30) and a collection strain (ATCC13637) of S. maltophilia. We had previously shown that the ATCC13637 strain has an attenuated phenotype in a zebrafish model of infection, as well as a distinct susceptibility profile against a panel of antimicrobials. The protein profiles of the OMP and OMV subproteomes of these two strains and their differences consequently point at pathogenesis, virulence or resistance proteins, such as two variants of the quorum-sensing factor Ax21 that are found to be highly abundant in the OMP fraction and exported to OMVs.

BIOLOGICAL SIGNIFICANCE

Stenotrophomonas maltophilia is rapidly climbing positions in the ranking of multidrug-resistant pathogens that are frequently isolated in hospital environments. Being an emerging human pathogen, the knowledge on the factors determining the pathogenicity, virulence and resistance traits of this microorganism is still scarce. Outer membrane proteins (OMPs) and vesicles (OMVs) are key elements for the interaction of Gram-negative bacteria with their environment -including the host-and have fundamental roles in both infection and resistance processes. The present study sets a first basis for a phenotype-dependent characterisation of the OMP subproteome of S. maltophilia and complements very recent work on the OMV subproteome of this species. The variability found among even two strains demonstrates once more that the analysis of genotypically and phenotypically distinct isolates under various conditions will be required before we can draw a significant picture of the OMP and OMV subproteomes of S. maltophilia.

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

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.

Draft Genome Sequence of Stenotrophomonas maltophilia Strain UV74 Reveals Extensive Variability within Its Genomic Group

We report the draft genome sequence of Stenotrophomonas maltophilia UV74, isolated from a vascular ulcer. This draft genome sequence shall contribute to the understanding of the evolution and pathogenicity of this species, particularly regarding isolates of clinical origin.