Elucidating the pathogenic repertoire of a bacterium

Abstract

Nosocomial infections, or those associated with clinical settings, present a major health and financial problem for healthcare infrastructure. In order to successfully prevent or treat these infections, we have to effectively identify pathogens as they arise and characterize the factors required for them to carry out their pathogenicity. While many higher priority pathogens have been able to be studied due to conventional detection methods, environmentally-derived or “rare” pathogens are often overlooked that may provide greater insight into shared mechanisms of virulence. Caulobacter, an aqueous- and soil-associated genus, has historically been thought to be non-pathogenic despite several clinical reports of Caulobacter-associated infections. Understanding the mechanism by which Caulobacter can persist in hospital settings and thrive within a human host to cause disease is critical, as this bacterium has been proposed as a tool both for environmental bioremediation and a clinical therapeutic. This work brings to light the potential pathogenicity of Caulobacter and seeks to holistically understand aspects of Caulobacter physiology facilitate pathogenesis or virulence. First, I use comparative genomics to describe a novel species of Caulobacter isolated from a patient. Furthermore, I use the in vivo infection model Galleria mellonella to describe a mechanism for virulence used by both clinical and environmental isolates in this model. Next, in order to holistically characterize Caulobacter in genetic screens, I created the first ordered transposon library in Caulobacter crescentus, the most widely studied species of the Caulobacters. This ordered library was used to screen for novel components that contribute to Caulobacter pathogenicity. Lastly, using the ordered library, I was able to both validate known aspects of Caulobacter physiology as well as identify novel determinants related to cell growth, surface attachment, motility, biofilm formation, and cell shape. Taken together, this work redefines our classical thinking of Caulobacter as “nonpathogen” while generating a tool for the community to better understand this bacterium.