| Vibrio fischeri uses two sequential quorum-sensing systems, AinSR and LuxIR, to coordinate the colonization of the squid Euprymna scolopes. The low-cell density AinSR system is required for both the initiation and persistence of the symbiosis, while the high-density LuxIR system is required for persistence. This thesis examines the role of AinSR quorum sensing in vitro and in vivo.;A previously reported growth-yield defect of ainS cultures was found to be due to the suppression of the acetate switch. The AinS-controlled induction of acs, the acetyl-CoA synthetase gene, is LuxIR-independent. An acs strain is at a competitive disadvantage when co-colonized with its wild-type parent, indicating that acs does contribute to V. fischeri colonization of E. scolopes.;The effect of synthetic autoinducers on quorum sensing provided an approach to test the distinct roles of these quorum-sensing systems during colonization. The data confirmed a LuxIR-independent effect of AinS on persistence in the light organ, and provided evidence of a factor, suppressed by the analogue 3-nitro phenylacetanoyl homoserine lactone, that is required for colonization in the absence of LitR.;Investigation of the AinS-regulated putative sigma factor, rpoQ , showed that RpoQ controls a portion of the AinS regulon that is dispensable for at least the early stages of host colonization. Microarray analysis identified RpoQ-independent AinS-controlled expression of genes, including those encoding iron uptake, a Type IV secretion system locus and exopolysaccharide production. |
