Indiana University-Purdue University Indianapolis (IUPUI) / Current Mycobacterium tuberculosis (Mtb) treatments suffer from an increase in antibiotic resistance strains and the lack of efficacy against latent state tuberculosis, thus novel approaches targeting different mechanisms of action are needed. One strategy to target Mtb is to target protein homeostasis pathways by inhibiting molecular chaperones, in particular, GroEL/ES (HSP60/10) chaperonin systems. Mtb has two homologs of GroEL, of which GroEL1 is not essential, but is important for cytokine-dependent granuloma formation, and GroEL2 is essential for survival and the likely canonical housekeeping chaperonin. Another strategy to target Mtb is to target the protein tyrosine phosphatase B (PtpB) virulence factor that Mtb secretes into host cells to help evade immune responses. Thus, we envisioned that this analog series might also be capable of inhibiting Mtb PtpB along with GroEL. By developing compound 1 inhibitors that could act on all of GroEL1, GroEL2, and PtpB, we could have an antibiotic candidate that targets all stages of tuberculosis: actively replicating bacteria, bacteria evading host cell immune response, and granuloma formation in latent disease. In the Johnson lab, previous studies explored GroEL/ES inhibitors, with compound 1 being one of the most potent inhibitors, inhibiting both Trypanosoma brucei and Staphylococcus aureus proliferation. In the present study, we have screened previously developed compound 1 analogs, as well as a series of newly synthesized analogs that we term “half-molecules”. In this study, our results indicated two potential avenues to explore for future research. The first is a series of carboxyl-bearing compound 1 inhibitors, compounds 2m-o, 2m-m, and 2m-p, which act solely on Mtb PtpB phosphatase activity without inhibiting GroEL. The second is a series of compound 1 inhibitors (e.g. 20R and 20L) that are able to inhibit both the PtpB phosphatase and GroEL/ES chaperonin system. Thus, this exploratory study showed the possibility of pursuing such a polypharmacological antibiotic strategy against Mtb infections and with further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis.

Indiana University-Purdue University Indianapolis (IUPUI) / Globally, millions of people die every year due to complications involving infections from antibiotic-resistant bacteria. Of these infections, the most common organisms are Mycobacterium tuberculosis (Mtb) and a group of bacteria known as the ESKAPE pathogens (an acronym that stands for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter species). Unfortunately, as the need for antibiotics increases, industrial antibiotic development programs are drying up. However, unique antibiotic candidates targeting new pathways may be better for addressing antibacterial resistance. A target that is currently not the focus of any drug on the market is the bacterial GroEL chaperonin system. GroEL chaperonins are complex, oligomeric proteins that are upregulated in the cell under stressful conditions and prevent the misfolding and aggregation of other proteins. All bacteria have one homolog that performs protein folding functions – such is the case for E. coli and the ESKAPE bacteria – while others, like M. tuberculosis, contain additional GroEL isoforms that appear to perform non-canonical functions that are not well understood. The canonical isoforms are essential for survival under all conditions; thus, these chaperonins represent excellent targets for antibiotic development. This study aimed to identify inhibitors of GroEL in the ESKAPE bacteria and Mtb from a library of compounds with known antibiotic properties that was provided by the Medicines for Malaria Venture. Using two orthogonal assays that assess GroEL activity via its refolding of denatured enzymes Malate Dehydrogenase and Rhodanase, 37 inhibitors of E. coli GroEL were identified. Of these, 33 were examined in dose response testing in in vitro biochemical and cell viability assays. Compound 23 stood out in potency for inhibiting GroEL functions and actively-replicating Mtb bacteria, and thus a small panel of analogs were evaluated to develop structure-activity relationships (SAR) and study their mechanism. Two cysteine residues were identified as covalently modified by compound 23 and one of the lead analogs, giving insight into inhibitory sites on GroEL. Another lead analog bearing a nitrofuran moiety exhibited inhibition of actively-replicating E. coli, S. aureus, and Mtb bacteria. Importantly, this study identified new classes of GroEL inhibitors to explore for optimization as antibacterial candidates. / 2024-07-06

The 105aa lambda S protein is the prototype holin, S accumulates in the cytoplasmic membrane during late gene expression until, at a time programmed into its primary structure, it disrupts the membrane and allows the lambda lysozyme, R, to attack the cell wall. In this study, a zwitterionic detergent Empigen BB, was used to extract and purify the lambda holin S. In Empigen BB, CD analysis on S gave 54% alpha helical content, consistent with 3 TM domains, which has been reported by other in vivo studies. Empigen BB-purified S can be exchanged into a chaotropic solution by dialysis and reconstituted into preformed lipid vesicles for activity assays. When diluted to fluorescein-loaded suspensions of liposomes, different chaotrope-solubilized S alleles caused dye release reflective of their in vivo phenotypes. The problem was the low efficiency of delivery of S to the liposomes. Unfortunately, dye loaded liposomes are highly sensitive to any detergent, making it necessary to find other ways to solubilize S. GroEL, a chaperonin from E. coli, is responsible for folding and refolding globular proteins in vitro. It has also been reported that GroEL improves the ability of a membrane protein synthesized in vitro to insert post-translationally into liposomes. This work will investigate the behavior of GroEL towards membrane proteins. The first of two membrane proteins studied in this respect is Bacteriorhodopsin (BR), a membrane proton pump, from H. halibium. The second is the105aa S protein, a prototype holin from bacteriophage lambda. Holin and BR subjected to detergent removal in the presence of GroEL remained in solution, while in the control sample (without GroEL) S and BR precipitated. "GroELsolubilized" holin still retained its lesion forming activity and solubilized BR maintained its proton pumping ability, detected by using a liposome dye activity assay unique to each protein. This approach may be applicable to other systems requiring detergent- or chaotrope-free preparation of membrane proteins. Finally, these results suggest that GroEL may be involved in the insertion of integral membrane proteins into the lipid bilayer, a role heretofore unsuspected.

Esta tesis se encuentra en proceso de registro como patente. / Antecedentes: La Enfermedad de Carrión es una patología importante que requiere un diagnóstico precoz para su manejo a fin de disminuir la morbimortalidad de la misma. Objetivo: Desarrollar una prueba inmunocromatográfica para la detección rápida de Bartonella bacilliformis usando anticuerpos policlonales de conejo etiquetados con oro coloidal. Metodología: Los anticuerpos policlonales contra Bartonella bacilliformis fueron obtenidos mediante la inmunización de conejos con la proteína GroEL de Bartonella bacilliformis. Se utilizó oro coloidal de 40 nm para la conjugación el anticuerpo primario obtenido. La sensibilidad analítica se evaluó con diferentes concentraciones de B. bacilliformis incluidas en un rango de 1x101 UFC/mL a 1x105 UFC/mL. La especificidad analítica o reacción cruzada se analizó con microorganismo de diferentes especies, incluyendo Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus viridans, Chlamydophila pneumoniae, Escherichia coli y Candida spp. Resultados: Las concentraciones óptimas del anticuerpo de captura y el anticuerpo de revestimiento (línea T) fueron de 2 mg/mL y 0.2 mg/mL respectivamente. Se determinó que la sensibilidad analítica de la prueba se encuentra en un rango de 1x102 UFC/mL y 1x101 UFC/mL. No se evidenciaron reacciones cruzadas con los microorganismos evaluados. Se determinó que el tiempo de corrida óptimo para el registro de resultados es de 20 minutos y el volumen mínimo requerido de la muestra analizada fue de 50 µL. Conclusión: Se desarrolló la primera prueba inmunocromatográfica para la detección rápida, sensible y específica de Bartonella bacilliformis utilizando anticuerpos policlonales contra la proteína GroEL, la cual deberá ser validada mediante estudios posteriores. / Background: Carrión's disease is an important disease that requires a timely diagnosis and management to reduce its morbimortality. Objective: Develop a lateral flow assay for the rapid detection of Bartonella bacilliformis using colloidal gold-labeled rabbit polyclonal antibodies. Materials and methods: Polyclonal antibodies against Bartonella bacilliformis were produced by the immunization of rabbits with GroEL protein purified from Bartonella bacilliformis. Colloidal gold of 40 nm was used for the conjugation process with the rabbit polyclonal antibodies. The analytical sensitivity was evaluated by testing solutions of B. bacilliformis with different concentrations ranging between 1 x 101 to 1 x 105 CFU/mL. Analytical specificity was determined by testing cross-reactivity with microorganisms from different species, including Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus viridans, Chlamydophila pneumoniae, Escherichia coli and Candida spp. Results: The optimal concentrations for the capture antibody and the coating antibody (T-line) were 2 mg / mL and 0.4 mg / mL, respectively. The analytical sensitivity was determined to be between 1x102 CFU/mL and 1x101 CFU/mL. There were no cross-reactions observed with the groups of bacteria used in this study. We determined that the flowing time and volume required for an optimum signal to be generated was 20 minutes and 50 µL, respectively. Conclusions: We developed the first gold-based lateral flow assay for the rapid, sensitive and specific detection of Bartonella bacilliformis using polyclonal antibodies against the protein GroEL, which needs to be validated in future studies. / Tesis

Dental caries, more commonly referred to as cavities or tooth decay, is a widespread disease in humans estimated to directly affect around 3.5 billion people worldwide. Following recent advances in molecular and genetic technologies over the last several decades, it is commonly understood that the human body is inhabited by a diverse and vast quantity of microorganisms, collectively referred to as the microbiome. The microbiome has been increasingly tied to fluctuations in both human health and disease. Current understandings of these interactions have shifted the model for many diseases, especially dental caries, to be the result of complex interplays between the human host and the microscopic organisms living around and within it. The molecular activities of several oral cavity bacteria are specifically significant in the initiation and progression of the caries process. These molecular activities are closely tied to regular fluctuations in the environment of the oral cavity, particularly acidification and dietary intake of carbohydrates, that select for the proliferation of cariogenic species of bacteria. Of particular interest in this thesis are species of the Actinomyces genus and how various environmental fluctuations influence the genetic expression of these bacteria and consequentially lead to the development of plaque on the enamel surface of human teeth. The caries process will be investigated through the lens of the most modern theory of caries progression, the Ecological Plaque Hypothesis, and the role of Actinomyces in this process will be considered. In this thesis, it is hypothesized that the extracellular expression of the common heat-shock protein (Hsp) known as GroEL is upregulated due to an increase in concentration of acidic byproducts produced by neighboring bacteria species as well as other environmental perturbations. The role of extracellular GroEL in attachment to the enamel surface by Actinomyces species was suggested to play an essential role in development of a cariogenic bacterial profile within enamel-associated plaque. This initial Actinomyces attachment and subsequent plaque proliferation is essential for the initiation of the caries process. Environmental and molecular factors such as short-chain fatty acids and variable pH will be considered as they are related to the development of carious lesions on the tooth surface. The impact of diet on this process will also be considered and this will be related to dietary discrepancies across various human populations in America. These factors will be tied together by looking at the oral health interventions being done by Boston University in the surrounding community, and conclusions regarding potential therapeutic practices will close out the discussion.

Caulobacter crescentus é uma bactéria Gram-negativa de vida livre cujo ciclo celular depende de eventos de diferenciação celular. A célula pré-divisional assimétrica dá origem a duas células filhas morfológica e funcionalmente distintas: a célula-talo e a célula móvel. A expressão do operon groESL é regulada por choque térmico e durante o ciclo celular a temperaturas normais, sendo a transcrição máxima na célula pré-divisional, com níveis baixos na célula-talo. Numa linhagem superexpressando σ32, os níveis do mRNA e da proteína GroEL estão aumentados, indicando que a transcrição ocorre a partir de um promotor ativado por σ32. A região regulatória também apresenta uma sequência repetida invertida, CIRCE, em que mutações de ponto aumentam a transcrição apenas a temperaturas normais de crescimento, indicando o papel inibitório desse elemento. Fusões de transcrição groESL-/acZ com mutações em CIRCE deixam de apresentar regulação temporal, bem como a síntese de GroEL numa linhagem hrcA-, em que o gene codificando o provável repressor que se liga em CIRCE está interrompido. Estes resultados indicam que o sistem CIRCE/HrcA está envolvido com a regulação da expressão de groESL durante o ciclo celular. Tentativas de se construir uma linhagem com groEL interrompido não tiveram sucesso, indicando ser este um gene essencial em todas as temperaturas. Um mutante condicional de groESL foi construído por recombinação homóloga e, em condições restritivas, o crescimento é inibido, os níveis de DnaK aumentam e as células se tomam filamentosas, porém não foi observada lise celular. As proteínas essenciais que são dependentes de GroEL/GroES para atingirem sua conformação funcional ainda não foram determinadas. / Caulobacter crescentus is an aquatic free-living Gram-negative bacterium whose cell cycle depends on cell differentiation. The asymmetrical predivisional cell gives rise to two morphologically and functionally different daughter cells: the swarmer cell an the stalked cell. The expression of the groESL operon is induced by heat shock and is cell cycle controlled at normal temperatures, with maximal transcription in the predivisional cell and very low levels in the stalked cell. In this work, it was demonstrated that, in a strain overexpressing σ32, the levels of groESL transcripts and the synthesis of GroEL are increased, confirming that this factor is responsible for the transcriptional activation of the σ32 -like promoter of this operon, that also presents a inverted repeat called CIRCE in its regulatory region. groESL-lacZ transcription fusions with point mutations in CIRCE indicated a negative role of this cis-acting element only at normal growth temperatures, with a minor effect on heat shock induction. In addition, the expression of these fusions are no longer cell-cycle regulated, as well as GroEL synthesis in a strain which does not have the HrcA protein, the putative repressor that binds CIRCE, indicating that the CIRCE-HrcA system are involved in cell cycle regulation of groESL in C. crescentus. It was also shown that groEL is an essential gene at normal growth temperatures, since a strain with groEL disrupted is not viable. A conditional mutant was obtained by homologous recombination and in restrictive conditions growth is inhibited, DnaK levels are increased and the cells become filamentous, but no celllysis was observed. The proteins that require GroEL/GroES for proper folding have not been identified yet.

Hintergrund: Gestillte Kinder haben im Vergleich zu nicht gestillten Kindern eine geringere Inzidenz von gastrointestinalen Infektionen und atopischen Erkrankungen. Man geht davon aus, dass der gesundheitsfördernde Effekt der Muttermilch teilweise über die intestinale Mikrobiota vermittelt wird. Diese ist in Stillkindern durch eine geringe Diversität und einen hohen Anteil an Bifidobakterien charakterisiert. Neueste Ansätze in der Weiterentwicklung industriell hergestellter Säuglingsnahrung zielen darauf ab, eine intestinale Mikrobiota zu fördern, die der von gestillten Kindern ähnelt. Die Supplementation von Säuglingsnahrung mit Probiotika (lebende Mikroorganismen) oder Präbiotika (unverdauliche Kohlenhydrate, die als Energiesubstrat für probiotische Bakterien dienen) könnte die bifidogene und antipathogene, aber auch immunmodulierende Wirkung der Muttermilch nachahmen. Aufgrund unterschiedlicher Interaktionen mit der Darmmikrobiota und dem Immunsystem fokussiert man mit der gleichzeitigen Gabe von Pro- und Präbiotika (Synbiotika) eine synergistische Wirkung an. Zielstellung und Studiendesign: In einer randomisiert-kontrollierten, klinischen Studie wurde untersucht, ob sich in den ersten drei Lebensmonaten von gesunden und termingerecht geborenen Kindern mit einer Synbiotikum-haltigen Säuglingsnahrung eine intestinale Mikrobiota etabliert, die der von gestillten Kindern gleicht. Das Synbiotikum setzte sich aus Bifidobacterium animalis ssp. lactis CNCM I 3446 (ältere Bezeichnung B. lactis BB-12) und Kuhmilcholigosacchariden zusammen. Die Studie umfasste zwei Gruppen von Kindern, die eine Säuglingsnahrung mit (SYN-Gruppe, n=21) oder ohne Supplement (KON-Gruppe, n=18) erhielten. Gestillte Kinder dienten als Referenz (REF-Gruppe, n=23). Um die Diversität der Bifidobakterien auf Speziesebene umfassend zu charakterisieren, wurden quantitative Real-Time PCR (qPCR)-Verfahren, basierend auf dem single-copy groEL als phylogenetisches Zielgen, zur spezifischen Quantifizierung von zwölf Bifidobakterienspezies in humanen Fäzes entwickelt und validiert. Ergebnisse: Die supplementierte Säuglingsnahrung war gut verträglich und unterstützte eine gesunde Entwicklung; vergleichbare anthropometrische Daten von SYN- und REF-Gruppe. Das Synbiotikum stimulierte selektiv das Wachstum von Laktobazillen und Bifidobakterien. Die Zellzahl für Laktobazillen der SYN-Gruppe war zur REF-Gruppe äquivalent (9,07±0,32 versus 9,90±0,27 log10 Zellen/g Fäzes TM [MW±SEM]; p<0,0019; Äquivalenzdifferenz von 1 log10 Zellen/g Fäzes TM) und höher als in der KON-Gruppe (8,27±0,31 log10 Zellen/g Fäzes TM [MW±SEM]). Die Zellzahl für Bifidobakterien war in der SYN-Gruppe am höchsten (11,54±0,05 versus 11,00±0,17 [REF-Gruppe] und 10,54±0,24 [KON-Gruppe] log10 Zellen/g Fäzes TM [MW±SEM]). In der SYN-Gruppe wurde die höchste Anzahl an Bifidobakterienspezies erfasst (167 mit [128 ohne] B. animalis in 56 Fäzesproben versus 98 und 93 in jeweils 51 Fäzesproben der REF- und KON-Gruppe). Neben Kinder-typischen Spezies wie B. bifidum und B. breve wurden auch Spezies, die für Erwachsene charakteristisch sind (B. adolescentis), häufiger in der SYN-Gruppe als in den Vergleichsgruppen nachgewiesen. Der pH-Wert in Fäzes von Kindern aus der SYN-Gruppe war niedriger als der aus der KON-Gruppe (6,07±0,20 versus 6,45±0,17 [MW±SEM]) und näher an dem von gestillten Kindern mit 5,29±0,12 (MW±SEM). Schlussfolgerung: Die Supplementation einer Säuglingsnahrung mit dem Synbiotikum aus CNCM I-3446 und Kuhmilcholigosacchariden führte zu einer Angleichung in der Zusammensetzung der intestinalen Mikrobiota und des fäkalen pH-Wertes an gestillte Kinder. Die in dieser Arbeit entwickelten groEL-basierten qPCR-Verfahren erlaubten eine spezifische und genaue Analyse der Bifidobakterienpopulation unter dem Einfluss eines Synbiotikums. / Background: Compared to formula-fed infants, breast-fed infants have a reduced incidence of gastrointestinal infections and atopic diseases. The health-promoting effect of breast milk is assumed to be partly mediated by the intestinal microbiota, which is characterized by a low diversity and a high proportion of bifidobacteria. Recent approaches in further development of infant formulae aim at promoting an intestinal microbiota similar to that of breast-fed infants. The supplementation of infant formula with probiotics (live microorganisms) or prebiotics (non-digestible carbohydrates, which serves as energy substrates for probiotic bacteria) could mimic the bifidogenic and antipathogenic, but also immunomodulating effect of breast milk. Due to various interactions with the gut microbiota and the immune system, the simultaneous administration of pro- and prebiotics (synbiotics) is focussed to have a synergistic effect. Objective and study design: In a randomized-controlled, clinical trial healthy full-term infants receiving an infant formula with synbiotic for the first three months of life were studied, whether an intestinal microbiota is induced, which is equivalent to that of breast-fed infants. The synbiotic consisted of Bifidobacterium animalis ssp. lactis CNCM I 3446 (previously known as B. lactis BB-12) and cow milk oligosaccharides. The study comprised two groups of infants receiving a starter formula with (SYN-group, n=21) or without supplement (KON-group, n=18). Breast-fed infants served as a reference (REF-group, n=23). In order to comprehensively characterize the bifidobacteria diversity at species level, quantitative real-time PCR (qPCR) assays based on the single-copy groEL as phylogenetic marker for the specific quantification of twelve bifidobacteria species in human feces were established and validated. Results: The supplemented formula was well tolerated and supported a healthy development; comparable anthropometric data of SYN- and REF-group. The synbiotic selectively stimulated the growth of lactobacilli and bifidobacteria. Lactobacilli levels were equivalent in SYN- and REF-group (9.07±0.32 versus 9.90±0.27 log10 cells/g feces DM [Mean±SEM]; p<0.0019; equivalence margin of 1 log10 cells/g feces DM) and higher than the KON-group (8.27±0.31 log10 cells/g feces DM [Mean±SEM]). The highest levels of bifidobacteria were observed in the SYN-group (11.54±0.05 versus 11.00±0.17 [REF-group] and 10.54±0.24 [KON-group] log10 cells/g feces DM [Mean±SEM]). The highest number of bifidobacteria species were obtained in the SYN-group (167 with [128 without] B. animalis in 56 fecal samples versus 98 and 93 in each of 51 fecal samples of the REF- and KON-group). Beside species, typically found in infants such as B. bifidum und B. breve, also species, which are characteristic for adults (B. adolescentis), were detected more often in the SYN-group than in the other study groups. Fecal pH was lower in the SYN- than in the KON-group 6.07±0.20 versus 6.45±0.17 [Mean±SEM]) and closer to that of breast-fed infants (5.29±0.12 [Mean±SEM]). Conclusion: In infants fed a starter formula supplemented with a synbiotic (CNCM I-3446 and cow milk oligosaccharides), composition of intestinal microbiota and fecal pH were closer to that of breast-fed infants. The groEL-based qPCR-assays, developed in this study, allowed a specific and accurate analysis of the bifidobacterial population in response to the synbiotic intake.

Caulobacter crescentus é uma bactéria Gram-negativa de vida livre cujo ciclo celular depende de eventos de diferenciação celular. A célula pré-divisional assimétrica dá origem a duas células filhas morfológica e funcionalmente distintas: a célula-talo e a célula móvel. A expressão do operon groESL é regulada por choque térmico e durante o ciclo celular a temperaturas normais, sendo a transcrição máxima na célula pré-divisional, com níveis baixos na célula-talo. Numa linhagem superexpressando &#963;32, os níveis do mRNA e da proteína GroEL estão aumentados, indicando que a transcrição ocorre a partir de um promotor ativado por &#963;32. A região regulatória também apresenta uma sequência repetida invertida, CIRCE, em que mutações de ponto aumentam a transcrição apenas a temperaturas normais de crescimento, indicando o papel inibitório desse elemento. Fusões de transcrição groESL-/acZ com mutações em CIRCE deixam de apresentar regulação temporal, bem como a síntese de GroEL numa linhagem hrcA-, em que o gene codificando o provável repressor que se liga em CIRCE está interrompido. Estes resultados indicam que o sistem CIRCE/HrcA está envolvido com a regulação da expressão de groESL durante o ciclo celular. Tentativas de se construir uma linhagem com groEL interrompido não tiveram sucesso, indicando ser este um gene essencial em todas as temperaturas. Um mutante condicional de groESL foi construído por recombinação homóloga e, em condições restritivas, o crescimento é inibido, os níveis de DnaK aumentam e as células se tomam filamentosas, porém não foi observada lise celular. As proteínas essenciais que são dependentes de GroEL/GroES para atingirem sua conformação funcional ainda não foram determinadas. / Caulobacter crescentus is an aquatic free-living Gram-negative bacterium whose cell cycle depends on cell differentiation. The asymmetrical predivisional cell gives rise to two morphologically and functionally different daughter cells: the swarmer cell an the stalked cell. The expression of the groESL operon is induced by heat shock and is cell cycle controlled at normal temperatures, with maximal transcription in the predivisional cell and very low levels in the stalked cell. In this work, it was demonstrated that, in a strain overexpressing &#963;32, the levels of groESL transcripts and the synthesis of GroEL are increased, confirming that this factor is responsible for the transcriptional activation of the &#963;32 -like promoter of this operon, that also presents a inverted repeat called CIRCE in its regulatory region. groESL-lacZ transcription fusions with point mutations in CIRCE indicated a negative role of this cis-acting element only at normal growth temperatures, with a minor effect on heat shock induction. In addition, the expression of these fusions are no longer cell-cycle regulated, as well as GroEL synthesis in a strain which does not have the HrcA protein, the putative repressor that binds CIRCE, indicating that the CIRCE-HrcA system are involved in cell cycle regulation of groESL in C. crescentus. It was also shown that groEL is an essential gene at normal growth temperatures, since a strain with groEL disrupted is not viable. A conditional mutant was obtained by homologous recombination and in restrictive conditions growth is inhibited, DnaK levels are increased and the cells become filamentous, but no celllysis was observed. The proteins that require GroEL/GroES for proper folding have not been identified yet.

<i>Escherichia coli</i> O157 is a food borne pathogen of increasing public health concern worldwide. Cattle have been implicated as the primary reservoir of <i>E. coli</i> O157. The fact that the livestock industry has rapidly expanded in Saskatchewan makes it imperative to have a clear scientific understanding of the prevalence of <i>E. coli</i> O157 in this province as well as its survival in soil under ambient conditions.<p>Longitudinal and point studies were employed to determine the prevalence of <i>E. coli</i> O157 among Saskatchewans cattle. During a 2-year period, 23 feedlot and cattle operations were examined and an overall prevalence of 15.6% was reported. The most important finding was that the prevalence rates were highly dependent on cattle density. All <i>E. coli</i> O157 isolates obtained from this study were characterized by using multiplex PCR, RAPD fingerprinting, a Vero cell cytotoxicity assay and antibiotic susceptibility tests. This characterization revealed a surprisingly highly virulent and heterogenous population of <i>E. coli</i> O157 isolates. <p>Subsequently, the survival characteristics of <i>E. coli</i> O157:H7 ATCC 43894 in sterile soil and manure-amended soil microcosms, as well as in situ under ambient environmental conditions were examined. Findings from this work indicated that desiccation had the most lethal effect on cell viability, whereas nutritionally-rich soils significantly increased survival times of the pathogen population. <p>A final study was designed to examine the survival strategy of hyper- and hypothermally adapted <i>E. coli</i> O157 cells exposed to high and low temperatures, with specific focus on the role of RpoS. Using wild type and its rpoS null allele <i>E. coli</i> O157 strains, in combination with 2D PAGE, It was found that both heat and cold post-acclimation stimulons consisted of two large sub-groups: (i) stress proteins, and (ii) housekeeping proteins. Comparative proteomic analyses revealed that the GroEL/S chaperonin complex and Pnp ribonuclease played a crucial role in growth resumption during high and low temperatures, respectively. Notably, RpoS had no control over key stress proteins in either stress stimulon. RpoS, however, showed a significantly more pronounced role during cold temperatures, where it was seen to regulate key proteins involved in homoeoviscous adaptation as well as various housekeeping proteins of both stress stimulons.

<i>Escherichia coli</i> O157 is a food borne pathogen of increasing public health concern worldwide. Cattle have been implicated as the primary reservoir of <i>E. coli</i> O157. The fact that the livestock industry has rapidly expanded in Saskatchewan makes it imperative to have a clear scientific understanding of the prevalence of <i>E. coli</i> O157 in this province as well as its survival in soil under ambient conditions.<p>Longitudinal and point studies were employed to determine the prevalence of <i>E. coli</i> O157 among Saskatchewans cattle. During a 2-year period, 23 feedlot and cattle operations were examined and an overall prevalence of 15.6% was reported. The most important finding was that the prevalence rates were highly dependent on cattle density. All <i>E. coli</i> O157 isolates obtained from this study were characterized by using multiplex PCR, RAPD fingerprinting, a Vero cell cytotoxicity assay and antibiotic susceptibility tests. This characterization revealed a surprisingly highly virulent and heterogenous population of <i>E. coli</i> O157 isolates. <p>Subsequently, the survival characteristics of <i>E. coli</i> O157:H7 ATCC 43894 in sterile soil and manure-amended soil microcosms, as well as in situ under ambient environmental conditions were examined. Findings from this work indicated that desiccation had the most lethal effect on cell viability, whereas nutritionally-rich soils significantly increased survival times of the pathogen population. <p>A final study was designed to examine the survival strategy of hyper- and hypothermally adapted <i>E. coli</i> O157 cells exposed to high and low temperatures, with specific focus on the role of RpoS. Using wild type and its rpoS null allele <i>E. coli</i> O157 strains, in combination with 2D PAGE, It was found that both heat and cold post-acclimation stimulons consisted of two large sub-groups: (i) stress proteins, and (ii) housekeeping proteins. Comparative proteomic analyses revealed that the GroEL/S chaperonin complex and Pnp ribonuclease played a crucial role in growth resumption during high and low temperatures, respectively. Notably, RpoS had no control over key stress proteins in either stress stimulon. RpoS, however, showed a significantly more pronounced role during cold temperatures, where it was seen to regulate key proteins involved in homoeoviscous adaptation as well as various housekeeping proteins of both stress stimulons.