The current work in our laboratory probes the mechanism of biofilm formation in the context of an animal host. Biofilms are multi-cellular communities of microorganisms, in which individual cells are protected from the environment by virtue of being (1) encased in a protective matrix comprised of polysaccharides and other macromolecules and (2) physiologically distinct from free-living, planktonic cells. Due to their resistance to antimicrobials such as antibiotics, biofilms play important roles in human health. To understand biofilm formation in the context of an animal host, we study the marine bioluminescent marine bacterium Vibrio fischeri and its symbiotic host, the small Hawaiian squid Euprymna scolopes.
Our investigation of the genetic requirements for symbiotic colonization led to the identification of the sensor kinase gene rscS and the 18-gene symbiosis polysaccharide (syp) locus, which encodes proteins involved in producing the polysaccharide component of the biofilm matrix. Mutations in either rscS or syp result in a profound colonization defect, likely due to their defect in forming symbiotic aggregates. Furthermore, overexpression of rscS from a multi-copy plasmid induced the production of syp-dependent biofilms in culture, including the formation of wrinkled colonies (instead of the smooth colonies of the wild-type strain) and strong pellicles (that are never produced by the wild-type strain). Importantly, overexpression of rscS also resulted in an enhanced ability of V. fischeri to form symbiotic aggregates and an increased ability to compete for colonization. The robust correlation of the ability to form biofilms in laboratory culture with formation of aggregates in the host and with colonization competence makes the V. fischeri-squid symbiosis a prime model for understanding the development of a biofilm in the context of an animal host.
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Loyola University Chicago Stritch School of Medicine.