Chemical Processes That Govern the Natural Attenuation of Microbial Signals: Environments That Simulate Photosynthetic Biofilms

Microbial quorum sensing is a form of chemical communication that is dependent on transmission of molecular signals through the environment. Complex molecular structures, including molecules used in microbial communication, are degraded in the environment through a manifold of reactions collectively referred to as \u27natural attenuation.\u27 Mechanisms of natural attenuation include oxidation, substitution, photolysis, etc, largely as function of the local conditions. This implies that natural attenuation can inhibit microbial self-detection mechanisms such as those used in the formation of microbial biofilms. This thesis focuses on the natural attenuation of two groups of chemicals used in microbial communication, the acylhomoserine lactones (AHLs) and a family of 4,5-dihydroxy-2,3-pentanedione (DPD) derivatives functionally classified as autoinducer-2 (AI2). Oxidative attenuation of the acylhomoserine lactones (AHLs) by hydroxyl radicals results in the formation of keto- and hydroxo AHLs, some of which are more potent signals (per mole) than the original AHLs. In contrast, parallel oxidation and hydrolysis of the AHLs results in the formation of inactive products under environmentally relevant conditions. Chemical communication based on the AI2 family is also subject to disruption through hydrolysis. DPD is a weak signal, but under marine conditions rapidly reacts with native boronate to yield (3aS,6S,6aR)-2,2,6,6a-tetrahydroxy-3a-methyltetrahydrofuro[2,3-d][1,3,2]dioxaborol-2-uide (commonly referred to as AI2). The equilibrium constant and boron self-exchange rates for this complex were measured under a variety of solution conditions relevant to a geographical range corresponding from fresh surface water to photosynthetic marine biofilms. The equilibrium for AI2 deesterification is rapid on the timescale of pH fluctuation in natural waters (i.e. in the intercellular fluid of photosynthetic biofilms), suggesting diel sensitivity for AI2 based quorum sensing in surface waters and photosynthetic films. Implications of these findings for chemical communication in dynamic environments such as tide marshes and water distribution pipes are discussed