Genetic Mechanisms and Community Dynamics of Bacterial Social Behaviors in Roseobacter member Rhodobacterales strain. Y4I

Quorum sensing (QS) allows bacterial populations to coordinate gene expression, typically in a cell density-dependent manner. Through the production and recognition of small diffusible signaling molecules, called autoinducers, bacteria can elicit group-level behaviors. Prevalent classes of autoinducers in Proteobacteria are N-acyl-homoserine lactones (AHL). Exchanges of AHLs in bacterial social engagements allow the regulation of cooperative and competitive interactions contributing to biofilm formation. Biofilms have both clinical and ecological relevance. In marine ecosystems, microbial biofilms contribute to biofouling of equipment, bioremediation of pollutants and transform organic matter which influences global biogeochemical cycles. Early microbial colonizers, such as representatives of the marine Roseobacter Clade, are hypothesized to ‘set the stage’ for biofilm structure, function, and dynamics via AHL-mediated QS. A necessary first step in understanding how bacterial social behaviors, such as cooperation and competition, influence interactions within biofilms are performing genetic analysis on primary surface colonizers. In Chapter 2, the QS systems of a competitive primary surface colonizer within the Roseobacter Clade, Rhodobacterales strain Y4I, are characterized. The work presented in this chapter demonstrates QS in Y4I is hierarchical. The findings provide a mechanistic understanding of physiological processes important in revealing genetic mechanisms facilitating competitiveness in Roseobacters. Chapter 3 highlights how QS within a microbial biofilm influences community structure and dynamics. The findings within suggests that inactivation of QS in a dominant community member, Y4I, result in increased community cooperation. These data support the hypothesis that primary surface colonizers ‘set the stage’ for community structure and dynamics in marine ecosystems. In Chapter 4, a model of the DNA regulatory binding site for QS was built to probe Roseobacter genomes for QS-regulated genes. The results presented in this chapter illuminate the genetic diversity within the Phaeobacter-Leisingera subclade of Roseobacters. Together, the works presented in this dissertation provide the necessary framework for espousing genetic understanding of QS to culture-based studies using multispecies biofilms. Furthermore, this dissertation provides a rudimentary motif model for probing QS-regulated genes within genomes.