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- All Subjects: Escherichia coli
- Creators: Misra, Rajeev
Description
The study of bacterial resistance to antimicrobial peptides (AMPs) is a significant area of interest as these peptides have the potential to be developed into alternative drug therapies to combat microbial pathogens. AMPs represent a class of host-mediated factors that function to prevent microbial infection of their host and serve as a first line of defense. To date, over 1,000 AMPs of various natures have been predicted or experimentally characterized. Their potent bactericidal activities and broad-based target repertoire make them a promising next-generation pharmaceutical therapy to combat bacterial pathogens. It is important to understand the molecular mechanisms, both genetic and physiological, that bacteria employ to circumvent the bactericidal activities of AMPs. These understandings will allow researchers to overcome challenges posed with the development of new drug therapies; as well as identify, at a fundamental level, how bacteria are able to adapt and survive within varied host environments. Here, results are presented from the first reported large scale, systematic screen in which the Keio collection of ~4,000 Escherichia coli deletion mutants were challenged against physiologically significant AMPs to identify genes required for resistance. Less than 3% of the total number of genes on the E. coli chromosome was determined to contribute to bacterial resistance to at least one AMP analyzed in the screen. Further, the screen implicated a single cellular component (enterobacterial common antigen, ECA) and a single transporter system (twin-arginine transporter, Tat) as being required for resistance to each AMP class. Using antimicrobial resistance as a tool to identify novel genetic mechanisms, subsequent analyses were able to identify a two-component system, CpxR/CpxA, as a global regulator in bacterial resistance to AMPs. Multiple previously characterized CpxR/A members, as well as members found in this study, were identified in the screen. Notably, CpxR/A was found to transcriptionally regulate the gene cluster responsible for the biosynthesis of the ECA. Thus, a novel genetic mechanism was uncovered that directly correlates with a physiologically significant cellular component that appears to globally contribute to bacterial resistance to AMPs.
ContributorsWeatherspoon-Griffin, Natasha (Author) / Shi, Yixin (Thesis advisor) / Clark-Curtiss, Josephine (Committee member) / Misra, Rajeev (Committee member) / Nickerson, Cheryl (Committee member) / Stout, Valerie (Committee member) / Arizona State University (Publisher)
Created2013
Description
Protein folding is essential in all cells, and misfolded proteins cause many diseases. In the Gram-negative bacterium Escherichia coli, protein folding must be carefully controlled during envelope biogenesis to maintain an effective permeability barrier between the cell and its environment. This study explores the relationship between envelope biogenesis and cell stress, and the return to homeostasis during envelope stress. A major player in envelope biogenesis and stress response is the periplasmic protease DegP. Work presented here explores the growth phenotypes of cells lacking degP, including temperature sensitivity and lowered cell viability. Intriguingly, these cells also accumulate novel cytosolic proteins in their envelope not present in wild-type. Association of novel proteins was found to be growth time- and temperature-dependent, and was reversible, suggesting a dynamic nature of the envelope stress response. Two-dimensional gel electrophoresis of envelopes followed by mass spectrometry identified numerous cytoplasmic proteins, including the elongation factor/chaperone TufA, illuminating a novel cytoplasmic response to envelope stress. A suppressor of temperature sensitivity was characterized which corrects the defect caused by the lack of degP. Through random Tn10 insertion analysis, aribitrarily-primed polymerase chain reaction and three-factor cross, the suppressor was identified as a novel duplication-truncation of rpoE, here called rpoE'. rpoE' serves to subtly increase RpoE levels in the cell, resulting in a slight elevation of the SigmaE stress response. It does so without significantly affecting steady-state levels of outer membrane proteins, but rather by increasing proteolysis in the envelope independently of DegP. A multicopy suppressor of temperature sensitivity in strains lacking degP and expressing mutant OmpC proteins, yfgC, was characterized. Bioinformatics suggests that YfgC is a metalloprotease, and mutation of conserved domains resulted in mislocalization of the protein. yfgC-null mutants displayed additive antibiotic sensitivity and growth defects when combined with null mutation in another periplasmic chaperone, surA, suggesting that the two act in separate pathways during envelope biogenesis. Overexpression of YfgC6his altered steady-state levels of mutant OmpC in the envelope, showing a direct relationship between it and a major constituent of the envelope. Curiously, purified YfgC6his showed an increased propensity for crosslinking in mutant, but not in a wild-type, OmpC background.
ContributorsLeiser, Owen Paul (Author) / Misra, Rajeev (Thesis advisor) / Jacobs, Bertram (Committee member) / Chang, Yung (Committee member) / Stout, Valerie (Committee member) / Arizona State University (Publisher)
Created2010
Description
Each year, more and more multi-drug resistant bacterial strains emerge, thus complicating treatment and increasing the average stay in the intensive care unit. As antibiotics are being rendered inefficient, there is a need to look into ways of weakening the internal state of bacterial cells to make them more susceptible to antibiotics. For this, we first need to understand what methods bacteria employ to fight against antibiotics. In this work, we have reviewed how bacteria respond to antibiotics. There is a similarity in response to antibiotic exposure and starvation (stringent stress) which changes the metabolic state. We have delineated what metabolism changes take place and how they are associated with oxidative stress. For example, there is a common change in NADH concentration that is tied to both metabolism and oxidative stress. Finally, we have compared the findings in literature with our research on an antibiotic-resistant RNA polymerase mutant that alters the gene expression profile in the general areas of metabolism and oxidative stress. Based on this thesis, we have suggested a couple of strategies to make antibiotics more efficient; however, as antibiotic-mediated killing is very complex, researchers need to delve deeper to understand and manipulate the full cellular response.
ContributorsPredtechenskaya, Maria (Author) / Misra, Rajeev (Thesis director) / Varman, Arul Mozhy (Committee member) / Mhatre, Apurv (Committee member) / Computer Science and Engineering Program (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05