The symbiosis regulator RscS controls the syp gene locus, biofilm formation and symbiotic aggregation by Vibrio fischeri

Abstract

SummarySuccessful colonization of a eukaryotic host by a microbe involves complex microbe-microbe and microbe-host interactions. Previously, we identified in Vibrio fischeri a putative sensor kinase, RscS, required for initiating symbiotic colonization of its squid host Euprymna scolopes. Here, we analysed the role of rscS by isolating an allele, rscS1, with increased activity. Multicopy rscS1 activated transcription of genes within the recently identified symbiosis polysaccharide (syp) cluster. Wild-type cells carrying rscS1 induced aggregation phenotypes in culture, including the formation of pellicles and wrinkled colonies, in a syp-dependent manner. Colonies formed by rscS1-expressing cells produced a matrix not found in control colonies and largely lost in an rscS1-expressing sypN mutant. Finally, multicopy rscS1 provided a colonization advantage over control cells and substantially enhanced the ability of wildtype cells to aggregate on the surface of the symbiotic organ of E. scolopes; this latter phenotype similarly depended upon an intact syp locus. These results suggest that transcription induced by RscSmediated signal transduction plays a key role in colonization at the aggregation stage by modifying the cell surface and increasing the ability of the cells to adhere to one another and/or to squid-secreted mucus.

RscS Functions Upstream of SypG To Control the syp Locus and Biofilm Formation in Vibrio fischeri

“…1). Because this phenotype is similar to the loss of RscS-induced biofilm formation that occurs upon the disruption of structural genes such as sypN, which encodes a putative glycosyltransferase (42,43), we repeated our experiments using an in-frame deletion strain, ⌬sypG. We found that the ⌬sypG mutation also eliminated RscS-mediated attachment (Fig.…”

“…Like RscS, multicopy expression of sypG results in enhanced syp transcription and biofilm formation, as measured by glass attachment and pellicle formation (43); however, the pellicles are not as robust as those formed by RscS-overexpressing cells. In addition, the overexpression of SypG does not induce wrinkled-colony formation, another hallmark of RscS overexpression (42). Furthermore, the sypG gene is adjacent to two genes, sypE and sypF, that encode putative SK and RR proteins, respectively; thus, it is not clear whether SypG functions directly downstream of SypF or whether a more complicated regulatory scheme exists.…”

“…Recently, however, we established that RscS activates the expression of the symbiosis polysaccharide (syp) cluster of genes (42). This cluster is composed of 18 genes organized into at least five putative operons (A to E, F to H, I to L, M to O, and P to R) (43; E. A. Hussa, K. Geszvain, and K. L. Visick, unpublished data).…”

“…The syp gene products are predicted to function in polysaccharide synthesis and transport, and most are required for the initiation of symbiotic colonization (43). The overexpression of rscS results in the induction of syp transcription and syp-dependent biofilm formation (42).…”

Draft Genome Sequence of Vibrio fischeri SR5, a Strain Isolated from the Light Organ of the Mediterranean Squid Sepiola robusta

“…The islets often encode members of phosphotransferase systems (PTS) and other metabolic genes, suggesting that this strain may encode novel and/or enhanced metabolic capacities that enable the expanded host range relative to MJ11. Absent from SR5 are the ES114-specific biofilm regulator rscS (9,11) and the putative siderophore biosynthesis and receptor genes conserved between MJ11 and ES114 (VF_A0156 to VF_A0165). These observations suggest a number of intriguing issues for future studies as to what biological activities are required for squid colonization and how SR5 is able to efficiently colonize its natural host and the heterologous E. scolopes when MJ11 cannot.…”