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Title:How Escherichia coli uses environmental cysteine
Author(s):Zhou, Yidan
Director of Research:Imlay, James
Doctoral Committee Chair(s):Imlay, James
Doctoral Committee Member(s):Kuzminov, Andrei; Vanderpool, Cari; Kehl-Fie, Thomas
Department / Program:Microbiology
Discipline:Microbiology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Cysteine, utilization
Abstract:Sulfur is an essential element for all forms of life. Bacteria have dedicated importers for a range of sulfur containing molecules (cystine, sulfate, taurine, glutathione). These importers are induced when bacteria are sulfur limited. Once imported, these sulfur compounds are first converted into usable cysteine and then are incorporated into biomolecules; thus, one would expect that cysteine import would be the most economical route for cells to acquire sulfur. However, uniquely among the amino acid transporters, cysteine importers are poorly characterized in the microbial world. We have demonstrated that wild-type E. coli cannot assimilate cysteine as sulfur source in the presence of other amino acids. Four transporters have adventitious cysteine import activity, but they do not import cysteine when their natural substrates are around. If these four transporters are deleted, E. coli can no longer scavenge trace cysteine. The surprising lack of an effective route to assimilate sulfur from cysteine may be due to the problems that rapid cysteine import can cause. Does this mean that cysteine is of no use for E. coli? The story doesn’t end like this. E. coli possesses a cysteine-specific importer, called YhaO, that is induced only when external cysteine is abundant. Downstream of yhaO sits yhaM, encoding a cysteine desulfidase that degrades cysteine to pyruvate, ammonia, and hydrogen sulfide. We found that this process is fast enough to allow cells to use cysteine as sole carbon or nitrogen source. YhaM is the primary sulfide producer when cells are exposed to abundant cysteine. Expression data showed that yhaO was most strongly induced when E. coli grows on poor carbon sources. The strong induction did not occur when Crp was deleted, indicating that Crp may regulate YhaOM. Indeed, Crp null mutants could not grow on cysteine as sole carbon source. We conclude that extracellular cysteine is utilized as a carbon or nitrogen source rather than as a cysteine source for protein biosynthesis.
Issue Date:2021-12-01
Type:Thesis
URI:http://hdl.handle.net/2142/113970
Rights Information:Copyright 2021 Yidan Zhou
Date Available in IDEALS:2022-04-29
Date Deposited:2021-12


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