Control of the AinS/AinR pheromone-signaling system in Vibrio fischeri ES114

Abstract

Many bacteria use small pheromone molecules to regulate group behaviors. The marine bacterium Vibrio fischeri uses two distinct but integrated acyl-homoserine lactone (AHL) pheromone-signaling systems (PSS) to regulate behaviors during colonization of its host squid Euprymna scolopes, including induction of symbiotic bioluminescence. One V. fischeri PSS, consisting of LuxI and LuxR, was the first AHL-based system discovered and remains the archetype for similar AHL signaling found broadly throughout the phylum Proteobacteria. However, LuxI/LuxR itself is regulated along with several other genes by a second structurally unrelated AHL-based PSS that is specific to the Vibrionaceae family. This PSS, which is underpinned by AinS and AinR, is responsible for regulating behaviors associated with initiating the symbiosis with E. scolopes, and it represents part of a conserved “core” PSS within the Vibrionaceae. Despite its importance in V. fischeri, many aspects of AinS function are not well-understood. In this dissertation, I describe aspects of AinS regulation, AinR’s role in signal perception, and previously unknown mechanisms of cross-talk between AinS/AinR and LuxI/LuxR. I provide evidence that AinR has high sensitivity and low selectivity for a range of AHL pheromones. Additionally, I show that the presence of ainR in cis affects regulation of ainS, which appears related to a large inverted repeat in ainR. I also describe how spontaneous mutations affecting a PSS regulator downstream of AinS/AinR, LuxO, result in decreased ainSR expression and increased survivability when V. fischeri is grown in static culture. Finally, I explore additional levels of cross-talk between the Ain and Lux PSSs. Together, these results show how previously unknown connections between AinS/AinR, LuxI/LuxR, and the core Vibrio PSS finely tune regulation of symbiotic factors in response to changing environmental conditions. This work extends our knowledge of bacterial communication and its role in host-microbe and microbe-microbe interactions.