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Eavesdropping and Mannitol Sensitivity in Bacteria

Schwieters, Andrew M
http://orcid.org/0000-0003-3594-8128
http://rave.ohiolink.edu/etdc/view?acc_num=osu1732033625005434

Abstract Details

2024, Doctor of Philosophy, Ohio State University, Microbiology.
Bacteria can communicate with each other through the production, release, and detection of small molecules called N-acyl homoserine lactones (AHLs). In a subset of the family Enterobacteriaceae, including the well-known genera Salmonella and Escherichia, AHLs are not produced but these bacteria retain the ability to detect them through the LuxR-type protein SdiA. This strategy is referred to as eavesdropping: where one species may listen in on the communication of another. The role of SdiA-mediated eavesdropping in the lifecycle of these bacteria is unknown. To determine the function of eavesdropping, we first reviewed the available literature on SdiA. Since the initial discovery of SdiA, many studies have attempted to gain insight into its role by looking for mutant defects in various host systems, elucidating the SdiA regulon, or finding in vitro phenotypes. The literature on each topic is complex and interpretation must be measured and considerate of the methodology used. We next examined the role of Salmonella SdiA in several host systems, including house flies, mice, and plants. We also determined the SdiA regulons of Salmonella, E. coli, and Enterobacter cloacae. The house fly is a known mechanical vector of Salmonella with some evidence of a more dynamic interaction between host and bacteria. Based on the abundance of AHL synthase homologs in insect metagenomes, we hypothesized that SdiA played a role in the survival of Salmonella within house flies. After a series of experimental infections, the evidence suggests that sdiA mutants are highly advantaged over their wild-type competitor and that SdiA may have a negative effect on survival within house flies. Using a randomly barcoded transposon library (Barseq), we examined Salmonella fitness in mice that were co-infected with the AHL producing pathogen Yersinia enterocolitica. Consistent with previous reporting, sdiA and its regulon suffered no fitness defects during gastroenteritis. Finally, an experimental infection of plants indicated that SdiA is not active in either Angiosperms or soybeans. The regulon of SdiA is poorly understood. We sought to elucidate the SdiA regulons of two clinically relevant Salmonella serovars, Typhimurium and Typhi, using RNA-seq. Although more than two-hundred genes were suggested to be sdiA regulated by expressing sdiA from a plasmid, only 13-20 genes across 5-6 loci are sdiA regulated when expressed from its native position on the chromosome. Most sdiA regulated genes are hypothetical or have no known function or phenotype. We also determined that sdiA regulons in other species, specifically E. coli and E. cloacae, have some overlap with each other. The partial overlap of regulons suggests a common response to foreign AHLs. It remains to be determined what phenotype or phenotypes when these sdiA regulated genes are activated. Antibiotic resistance is a growing threat to the welfare of mankind. One of many approaches to tackling this great challenge is the identification of novel antimicrobial targets. One currently unexplored strategy is to attenuate bacteria by inducing sugar-phosphate toxicity. Bacterial metabolism uses many phosphorylated intermediates that are quickly interconverted in the cell. Inhibiting enzymes in the cell essential for the processing of certain intermediates leads to their accumulation and subsequent growth defects: the phenomenon of sugar-phosphate toxicity. We evaluated the therapeutic potential of mannitol-1-phosphate (Mtl-1P) toxicity, which is induced by inactivation of Mannitol-1-phosphate 5-dehydrogenase (MtlD) and the exogeneous introduction of mannitol. We found that mtlD mutants in the genera Cronobacter, Escherichia, Salmonella, and Pseudomonas are all inhibited in vitro by mannitol at micromolar concentrations. In vivo, we observed that both gastrointestinal and systemic infections of Salmonella mtlD mutants could be attenuated by providing mannitol to mice in their drinking water, suggesting a hypothetical MtlD inhibitor would be effective in treating infections. While investigating the mtlD mutant in vitro, we discovered a previously unreported phenotype in mtlD mutants, termed recovery. Recovery is the resumption of growth following intoxication and the delay between intoxication and recovery is dependent on the initial quantity of mannitol in the solution. Overall, the work in this thesis provides new insights into SdiA-mediated eavesdropping by identifying new regulon members in Salmonella, E. coli, and E. cloacae and investigating the role of SdiA in different host systems. In addition, we investigate the scope and therapeutic potential of mannitol sensitivity as a therapeutic target in bacteria, finding that all tested mtlD mutants are attenuated by the presence of mannitol and mtlD mutants are attenuated in multiple mouse models of infection.
Brian Ahmer (Advisor)
Chad Rappleye (Committee Member)
Sarah Short (Committee Member)
John Gunn (Committee Member)
288 p.
Microbiology
Salmonella, quorum sensing, eavesdropping, mannitol, sugar-phosphate toxicity

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Citations

  • Schwieters, A. M. (2024). Eavesdropping and Mannitol Sensitivity in Bacteria [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1732033625005434

    APA Style (7th edition)

  • Schwieters, Andrew. Eavesdropping and Mannitol Sensitivity in Bacteria. 2024. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1732033625005434.

    MLA Style (8th edition)

  • Schwieters, Andrew. "Eavesdropping and Mannitol Sensitivity in Bacteria." Doctoral dissertation, Ohio State University, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=osu1732033625005434

    Chicago Manual of Style (17th edition)

osu1732033625005434
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