The emergence of social evolution theories has been a game changer for the field of microbiology. We now know that bacteria, like many other gregarious organisms, display a wide array of social traits. In this sense, social evolution theories have been indispensable for understanding how bacteria function as multicellular communities where both coordinated and uncoordinated group behaviors can transpire that ultimately affect their fitness. Recently, the significance of these bacterial social interactions during infections has come to light, spurring a new wave of questions and research interests within microbiology. However, in understanding these complex interactions, a majority of the studies fail to recreate the environment encountered by bacteria in clinical settings. Therefore, we placed a particular emphasis on using experimental models that reflect physiological conditions. The first part of this thesis explores the role of two hemostasis factors of Staphylococcus aureus, staphylocoagualse (Coa) and von Willebrand factor binding protein (vWbp), in a social evolution context, and how they function as ‘public goods’. It demonstrates how S. aureus-induced clotting is a cooperative trait that can be exploited during infection. It establishes the virulence consequences and mixed community benefits associated with coagulases during hematogenous spread of S. aureus. In addition, the work incorporates murine models of infection where the defining pathophysiological events of staphylococcal abscesses and polymicrobial chronic wounds are taken into account in relation to the social dynamics associated with coagulases. A key finding of this study was the depth of clinical significance in relation to mixed communities being able to access the aforementioned public goods.
The secondary part of this thesis focuses on how Pseudomonas aeruginosa is able to maximize its fitness in two opposing niches by employing the strategy of responsive switching through its secondary messenger system c-di-GMP. The experimental conditions simulate the concepts of migration and resettlement of microbes to shed light on how global versus local competition affects the evolution of an ancestral lineage and the fitness consequences associated with responsive switching.