Sulfur Acquisition by the Marine Bacterium Vibrio fischeri Promotes the Establishment of a Mutualistic Symbiosis
Open Access
- Author:
- Wasilko, Nathan
- Graduate Program:
- Biochemistry, Microbiology, and Molecular Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 03, 2020
- Committee Members:
- Timothy Iwao Miyashiro, Dissertation Advisor/Co-Advisor
Timothy Iwao Miyashiro, Committee Chair/Co-Chair
Ken Keiler, Committee Member
Kathleen Postle, Committee Member
Todd C Lajeunesse, Outside Member
James Gregory Ferry, Committee Member
Wendy Hanna-Rose, Program Head/Chair - Keywords:
- Vibrionaceae
sulfate assimilation
squid-vibrio
sulfur
symbiosis - Abstract:
- Bacteria that positively impact the fitness of their host are described as bacterial symbionts. Bacterial growth is required for the establishment and maintenance of symbiotic populations within a host. The acquisition of environmental nutrients represents a linchpin for bacterial growth. Identifying the molecular mechanisms that contribute to bacterial growth within a host is significant for understanding how bacteria have evolved to fill specific ecological habitats. All bacteria require sulfur for growth. Bacteria maintain an intracellular pool of cysteine that serves as the sulfur source for many anabolic processes. Identifying how bacteria maintain their cysteine pools is significant for understanding the molecular mechanisms that promote bacterial growth within a host. A host-microbe relationship that is amendable for identifying factors that contribute to bacterial growth in vivo is the symbiosis established between the marine bacterium, Vibrio fischeri, and the Hawaiian bobtail squid, Euprymna scolopes. Shortly after hatching, a structure within the squid called the ‘light organ’, is exposed to V. fischeri cells within the surrounding seawater. V. fischeri cells that colonize the light organ rapidly grow on host-derived proteins and amino acids. Currently, the sulfur sources that are accessed by V. fischeri in the light organ for cellular growth are unknown. The transcription factor, CysB, is shown to be necessary for V. fischeri both to grow on several sulfur sources in vitro and to establish symbiosis with juvenile squid. Induction of a cystine importer is sufficient for V. fischeri to grow in vivo. Furthermore, genes involved in sulfate assimilation are shown to contribute to the growth of V. fischeri during symbiosis. We show the V. fischeri protein, YfbS, functions as a sulfate importer that contributes to symbiont growth within the light organ. Finally, CysB-regulated genes are shown to be differentially expressed among V. fischeri populations occupying the various colonization sites found within the light organ, suggesting the location of each V. fischeri population within the squid light organ impacts the physiology of this symbiotic bacterium. Together, these results reveal several mechanisms and sulfur sources that contribute to the growth of V. fischeri during symbiosis establishment.