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Description
Pathogenic Gram-negative bacteria employ a variety of molecular mechanisms to combat host defenses. Two-component regulatory systems (TCR systems) are the most ubiquitous signal transduction systems which regulate many genes required for virulence and survival of bacteria. In this study, I analyzed different TCR systems in two clinically-relevant Gram-negative bacteria, i.e., oral pathogen Porphyromonas gingivalis and enterobacterial Escherichia coli. P. gingivalis is a major causative agent of periodontal disease as well as systemic illnesses, like cardiovascular disease. A microarray study found that the putative PorY-PorX TCR system controls the secretion and maturation of virulence factors, as well as loci involved in the PorSS secretion system, which secretes proteinases, i.e., gingipains, responsible for periodontal disease. Proteomic analysis (SILAC) was used to improve the microarray data, reverse-transcription PCR to verify the proteomic data, and primer extension assay to determine the promoter regions of specific PorX regulated loci. I was able to characterize multiple genetic loci regulated by this TCR system, many of which play an essential role in hemagglutination and host-cell adhesion, and likely contribute to virulence in this bacterium. Enteric Gram-negative bacteria must withstand many host defenses such as digestive enzymes, low pH, and antimicrobial peptides (AMPs). The CpxR-CpxA TCR system of E. coli has been extensively characterized and shown to be required for protection against AMPs. Most recently, this TCR system has been shown to up-regulate the rfe-rff operon which encodes genes involved in the production of enterobacterial common antigen (ECA), and confers protection against a variety of AMPs. In this study, I utilized primer extension and DNase I footprinting to determine how CpxR regulates the ECA operon. My findings suggest that CpxR modulates transcription by directly binding to the rfe promoter. Multiple genetic and biochemical approaches were used to demonstrate that specific TCR systems contribute to regulation of virulence factors and resistance to host defenses in P. gingivalis and E. coli, respectively. Understanding these genetic circuits provides insight into strategies for pathogenesis and resistance to host defenses in Gram negative bacterial pathogens. Finally, these data provide compelling potential molecular targets for therapeutics to treat P. gingivalis and E. coli infections.
ContributorsLeonetti, Cori (Author) / Shi, Yixin (Thesis advisor) / Stout, Valerie (Committee member) / Nickerson, Cheryl (Committee member) / Sandrin, Todd (Committee member) / Arizona State University (Publisher)
Created2013
Description
This study was devised to elucidate key information concerning the potential risk posed by Legionella in reclaimed water. A series of biological experiments and a recharge basin soil column study were conducted to examine the survival, growth, and transport of L. pneumophila through engineered reclaimed water systems. A pilot-scale, column study was set up to measure Legionella transport in the columns under Arizona recharge basin conditions. Two columns, A and B, were packed to a depth of 122 cm with a loamy sand media collected from a recharge basin in Mesa, Arizona. The grain size distribution of Column A differed from that of Column B by the removal of fines passing the #200 sieve. The different soil profiles represented by column A and B allowed for further investigation of soil attributes which influence the microbial transport mechanism. Both clear PVC columns stand at a height of 1.83 m with an inner diameter of 6.35 cm. Sampling ports were drilled into the column at the soil depths 15, 30, 60, 92, 122 cm. Both columns were acclimated with tertiary treated waste water and set to a flow rate of approximately 1.5 m/d. The columns were used to assess the transport of a bacterial indicator, E. coli, in addition to assessing the study's primary pathogen of concern, Legionella. Approximately, 〖10〗^7 to 〖10〗^9 E. coli cells or 〖10〗^6 to 〖10〗^7Legionella cells were spiked into the columns' head waters for each experiment. Periodically, samples were collected from each column's sampling ports, until a minimum of three pore volume passed through the columns.
The pilot-scale, column study produced novel results which demonstrated the mechanism for Legionella to be transported through recharge basin soil. E. coli was transported, through 122 cm of the media in under 6 hours, whereas, Legionella was transported, through the same distance, in under 30 hours. Legionella has been shown to survive in low nutrient conditions for over a year. Given the novel results of this proof of concept study, a claim can be made for the transport of Legionella into groundwater aquifers through engineering recharge basin conditions, in Central Arizona.
The pilot-scale, column study produced novel results which demonstrated the mechanism for Legionella to be transported through recharge basin soil. E. coli was transported, through 122 cm of the media in under 6 hours, whereas, Legionella was transported, through the same distance, in under 30 hours. Legionella has been shown to survive in low nutrient conditions for over a year. Given the novel results of this proof of concept study, a claim can be made for the transport of Legionella into groundwater aquifers through engineering recharge basin conditions, in Central Arizona.
ContributorsMcBurnett, Lauren Rae (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2014
Description
With the aid of metabolic pathways engineering, microbes are finding increased use as biocatalysts to convert renewable biomass resources into fine chemicals, pharmaceuticals and other valuable compounds. These alternative, bio-based production routes offer distinct advantages over traditional synthesis methods, including lower energy requirements, rendering them as more "green" and "eco-friendly". Escherichia coli has recently been engineered to produce the aromatic chemicals (S)-styrene oxide and phenol directly from renewable glucose. Several factors, however, limit the viability of this approach, including low titers caused by product inhibition and/or low metabolic flux through the engineered pathways. This thesis focuses on addressing these concerns using magnetic mesoporous carbon powders as adsorbents for continuous, in-situ product removal as a means to alleviate such limitations. Using process engineering as a means to troubleshoot metabolic pathways by continuously removing products, increased yields are achieved from both pathways. By performing case studies in product toxicity and reaction equilibrium it was concluded that each step of a metabolic pathway can be optimized by the strategic use of in-situ adsorption as a process engineering tool.
ContributorsVasudevan, Anirudh (Author) / Nielsen, David R (Thesis advisor) / Torres, César I (Committee member) / Wang, Xuan (Committee member) / Arizona State University (Publisher)
Created2014
Description
In this thesis, I present a lab-on-a-chip (LOC) that can separate and detect Escherichia Coli (E. coli) in simulated urine samples for Urinary Tract Infection (UTI) diagnosis. The LOC consists of two (concentration and sensing) chambers connected in series and an integrated impedance detector. The two-chamber approach is designed to reduce the non-specific absorption of proteins, e.g. albumin, that potentially co-exist with E. coli in urine. I directly separate E. coli K-12 from a urine cocktail in a concentration chamber containing micro-sized magnetic beads (5 µm in diameter) conjugated with anti-E. coli antibodies. The immobilized E. coli are transferred to a sensing chamber for the impedance measurement. The measurement at the concentration chamber suffers from non-specific absorption of albumin on the gold electrode, which may lead to a false positive response. By contrast, the measured impedance at the sensing chamber shows ~60 kÙ impedance change between 6.4x104 and 6.4x105 CFU/mL, covering the threshold of UTI (105 CFU/mL). The sensitivity of the LOC for detecting E. coli is characterized to be at least 3.4x104 CFU/mL. I also characterized the LOC for different age groups and white blood cell spiked samples. These preliminary data show promising potential for application in portable LOC devices for UTI detection.
ContributorsKim, Sangpyeong (Author) / Chae, Junseok (Thesis advisor) / Phillips, Stephen M. (Committee member) / Blain Christen, Jennifer M. (Committee member) / Arizona State University (Publisher)
Created2011
Description
The diversity of industrially important chemicals that can be produced biocatalytically from renewable resources continues to expand with the aid of metabolic and pathway engineering. In addition to biofuels, these chemicals also include a number of monomers with utility in conventional and novel plastic materials production. Monomers used for polyamide production are no exception, as evidenced by the recent engineering of microbial biocatalysts to produce cadaverine, putrescine, and succinate. In this thesis the repertoire and depth of these renewable polyamide precursors is expanded upon through the engineering of a novel pathway that enables Escherichia coli to produce, as individual products, both δ-aminovaleric acid (AMV) and glutaric acid when grown in glucose mineral salt medium. δ-Aminovaleric acid is the monomeric subunit of nylon-5 homopolymer, whereas glutaric acid is a dicarboxylic acid used to produce copolymers such as nylon-5,5. These feats were achieved by increasing endogenous production of the required pathway precursor, L-lysine. E. coli was engineered for L-lysine over-production through the introduction and expression of metabolically deregulated pathway genes, namely aspartate kinase III and dihydrodipicolinate synthase, encoded by the feedback resistant mutants lysCfbr and dapAfbr, respectively. After deleting a natural L-lysine decarboxylase, up to 1.6 g/L L-lysine could be produced from glucose in shake flasks as a result. The natural L-lysine degradation pathway of numerous Pseudomonas sp., which passes from L-lysine through both δ-aminovaleric acid and glutaric acid, was then functionally reconstructed in a piecewise manner in the E. coli L-lysine over-producer. Expression of davBA alone resulted in the production of over 0.86 g/L AMV in 48 h. Expression of davBADT resulted in the production of over 0.82 g/L glutaric acid under the same conditions. These production titers were achieved with yields of 69.5 and 68.4 mmol/mol of AMV and glutarate, respectively. Future improvements to the ability to synthesize both products will likely come from the ability to eliminate cadaverine by-product formation through the deletion of cadA and ldcC, genes involved in E. coli's native lysine degradation pathway. Nevertheless, through metabolic and pathway engineering, it is now possible produce the polyamide monomers of δ-aminovaleric acid and glutaric acid from renewable resources.
ContributorsAdkins, Jake M (Author) / Nielsen, David R. (Thesis advisor) / Caplan, Michael (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2012
Description
The need for rapid, specific and sensitive assays that provide a detection of bacterial indicators are important for monitoring water quality. Rapid detection using biosensor is a novel approach for microbiological testing applications. Besides, validation of rapid methods is an obstacle in adoption of such new bio-sensing technologies. In this study, the strategy developed is based on using the compound 4-methylumbelliferyl glucuronide (MUG), which is hydrolyzed rapidly by the action of E. coli β-D-glucuronidase (GUD) enzyme to yield a fluorogenic product that can be quantified and directly related to the number of E. coli cells present in water samples. The detection time required for the biosensor response ranged from 30 to 120 minutes, depending on the number of bacteria. The specificity of the MUG based biosensor platform assay for the detection of E. coli was examined by pure cultures of non-target bacterial genera and also non-target substrates. GUD activity was found to be specific for E. coli and no such enzymatic activity was detected in other species. Moreover, the sensitivity of rapid enzymatic assays was investigated and repeatedly determined to be less than 10 E. coli cells per reaction vial concentrated from 100 mL of water samples. The applicability of the method was tested by performing fluorescence assays under pure and mixed bacterial flora in environmental samples. In addition, the procedural QA/QC for routine monitoring of drinking water samples have been validated by comparing the performance of the biosensor platform for the detection of E. coli and culture-based standard techniques such as Membrane Filtration (MF). The results of this study indicated that the fluorescence signals generated in samples using specific substrate molecules can be utilized to develop a bio-sensing platform for the detection of E. coli in drinking water. The procedural QA/QC of the biosensor will provide both industry and regulatory authorities a useful tool for near real-time monitoring of E. coli in drinking water samples. Furthermore, this system can be applied independently or in conjunction with other methods as a part of an array of biochemical assays in order to reliably detect E. coli in water.
ContributorsHesari, Nikou (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Fox, Peter (Committee member) / Stout, Valerie (Committee member) / Arizona State University (Publisher)
Created2015
ContributorsEvans, Bartlett R. (Conductor) / Schildkret, David (Conductor) / Glenn, Erica (Conductor) / Concert Choir (Performer) / Chamber Singers (Performer) / ASU Library. Music Library (Publisher)
Created2018-03-16
Description
Synthetic biology and metabolic engineering has aided the production of chemicals using renewable resources, thus offering a solution to our dependence on the dwindling petroleum resources. While a major portion of petroleum resources go towards production of fuels, a significant fraction also goes towards production of specialty chemicals. There has been a growing interest in recent years in commercializing bio-based production of such high value compounds. In this thesis the biosynthesis of aromatic esters has been explored, which have typical application as flavor and fragrance additive to food, drinks and cosmetics. Recent progress in pathway engineering has led to the construction of several aromatic alcohol producing pathways, the likes of which can be utilized to engineer aromatic ester biosynthesis by addition of a suitable enzyme from the acyltransferase class. Enzyme selection and screening done in this work has identified chloramphenicol O-acetyltransferase enzyme(CAT) as a potential candidate to complete the biosynthetic pathways for each of 2-phenethyl acetate, benzyl acetate, phenyl acetate and acetyl salicylate. In the end, E. coli strains capable of producing up to 60 mg/L 2-phenethyl acetate directly from glucose were successfully constructed by co-expressing CAT in a previously engineered 2-phenylethanol producing host.
ContributorsMadathil Soman Pillai, Karthika (Author) / Nielsen, David (Thesis advisor) / Wang, Xuan (Committee member) / Torres, Cesar (Committee member) / Arizona State University (Publisher)
Created2016
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