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Title:Understanding the intrinsic antibiotic resistance in Lysobacter enzymogenes, a ubiquitous environmental bacterium
Author(s):Yu, Menghao
Director of Research:Zhao, Youfu
Doctoral Committee Chair(s):Zhao, Youfu
Doctoral Committee Member(s):Schroeder, Nathan; Mideros, Santiago; Hind, Sarah Refi
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Lysobacter
Intrinsic resistance
Ampicillin
Spectinomycin
CsrA
Abstract:Antibiotics are one of the most important tools in modern medicine. Unfortunately, due to frequent use of antibiotics in clinical and agricultural areas, more bacterial strains in diverse environmental settings have been found to be resistant to many antibiotics, resulting in multidrug resistance (MDR). Increased understanding of antibiotic resistance in environmental bacteria provides new targets for discovery of novel therapeutics. However, little is known about the antibiotic resistance of the vast majority of environmental bacteria. The ubiquitous Gram-negative Lysobacter bacteria, as promising biocontrol agents, confer intrinsic antibiotic resistance and could be used as a model in understanding antibiotic resistance in non-clinical environments. First, to fill a critical knowledge gap in the prevalence and diversity of MDR in Lysobacter, we compared two strains of Lysobacter species, i.e., LeC3 and LaATCC29479, and determined their resistance to 12 common antibiotics. Our results revealed that both strains exhibited high level of MDR, and in comparison to LaATCC29479, LeC3 exhibited even higher levels of resistance against most antibiotics tested compared to LaATCC29479. Comparative resistomic analyses identified the core resistome of Lysobacter and also revealed potential genes related to the antibiotic resistance profiles in LeC3 and LaATCC29479. Second, screening two Tn5 transposon mutant libraries of LeC3 recovered 12 and 19 mutants with decreased ampicillin and spectinomycin resistance, respectively. Further characterization of selected mutants showed that cell permeability, β-lactamase activity and transport contributed to high level of resistance to ampicillin in LeC3; whereas high level of resistance to spectinomycin in LeC3 was mostly due to its ribosomal RNA target as well as related to cell-wall recycling and purine biosynthesis. Third, we demonstrated that the post-transcriptional regulator CsrA not only conferred MDR, but also contributed to biocontrol activity in LeC3. Furthermore, two putative small regulatory RNAs (sRNAs), referred to as csrB and csrC, were identified in the genome of LeC3. Double mutation of csrB and csrC in LeC3 led to increased resistance to nalidixic acid, rifampicin, and kanamycin. Collectively, this project paves the way for further MDR studies using Lysobacter bacteria.
Issue Date:2020-07-10
Type:Thesis
URI:http://hdl.handle.net/2142/108670
Rights Information:Copyright 2020 Menghao Yu
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08


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