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The microbial diversity and biogeochemical potential associated with a northern Saskatchewan uranium mine water-tailings interface was examined using culture-dependent and -independent techniques. Morphologically-distinct colonies from uranium mine water-tailings and a reference lake (MC) obtained using selective and non-selective media were selected for 16S rRNA gene sequencing and identification, revealing that culturable organisms from the uranium tailings interface were dominated by Firmicutes and Betaproteobacteria; whereas, MC organisms mainly consisted of Bacteroidetes and Gammaproteobacteria. Ion Torrent (IT) 16S rRNA metagenomic analysis carried out on extracted DNA from tailings and MC interfaces demonstrated the dominance of Firmicutes in both of the systems. Overall, the tailings-water interface environment harbored a distinct bacterial community relative to the MC, reflective of the ambient conditions (i.e., total dissolved solids, pH, salinity, conductivity, heavy metals) dominating the uranium tailings system. Significant correlations among the physicochemical data and the major bacterial groups present in the tailings and MC were also observed. Presence of sulfate reducing bacteria demonstrated by culture-dependent analyses and the dominance of Desulfosporosinus spp. indicated by Ion Torrent analyses within the tailings-water interface suggests the existence of anaerobic microenvironments along with the potential for reductive metabolic processes.

A population-based study combining (i) antimicrobial, (ii) genetic, and (iii) virulence analyses with molecular evolutionary analyses revealed segregative characteristics distinguishing human clinical and bovine Escherichia coli O157 strains from western Canada. Human ( n = 50) and bovine ( n = 50) strains of E. coli O157 were collected from Saskatchewan and Manitoba in 2006 and were analyzed by using the six-marker lineage-specific polymorphism assay (LSPA6), antimicrobial susceptibility analysis, the colicin assay, plasmid and virulence profiling including the eae , ehxA , espA , iha , stx 1 , stx 2 , stx 2c , stx 2d , stx 2d-activatable , stx 2e , and stx 2f virulence-associated genes, and structure analyses. Multivariate logistic regression and Fisher's exact test strongly suggested that antimicrobial susceptibility was the most distinctive characteristic ( P = 0.00487) associated with human strains. Among all genetic, virulence, and antimicrobial determinants, resistance to tetracycline ( P < 0.000) and to sulfisoxazole ( P < 0.009) were the most strongly associated segregative characteristics of bovine E. coli O157 strains. Among 11 virulence-associated genes, stx 2c showed the strongest association with E. coli O157 strains of bovine origin. LSPA6 genotyping showed the dominance of the lineage I genotype among clinical (90%) and bovine (70%) strains, indicating the importance of lineage I in O157 epidemiology and ecology. Population structure analysis revealed that the more-diverse bovine strains came from a unique group of strains characterized by a high degree of antimicrobial resistance and high frequencies of lineage II genotypes and stx 2c variants. These findings imply that antimicrobial resistance generated among bovine strains of E. coli O157 has a large impact on the population of this human pathogen.

Deterioration of water wells due to clogging and corrosion over time is a common problem where solutions may be costly and ineffective. Pilot studies have suggested that impressed current or cathodic protection may be used to reduce microbially-induced declines in water well performance. Two water wells in an alluvial aquifer close to the North Saskatchewan River were selected to study the response of subsurface microbial communities to the application of an impressed current as an anti-fouling technology. The treated well was exposed to an impressed current while the untreated well was used as a reference site. Biofilms grown on in situ coupons under the influence of the impressed current were significantly (p

Relatively little is known regarding the spatial variability of microbial communities in aquifers where well fouling is an issue. In this study 2 water wells were installed in an alluvial aquifer located adjacent to the North Saskatchewan River and an associated piezometer network developed to facilitate the study of microbial community structure, richness, and diversity. Carbon utilization data analysis revealed reduced microbial activity in waters collected close to the wells. Functional PCR and quantitative PCR analysis indicated spatial variability in the potential for iron-, sulphate-, and nitrate-reducing activity at all locations in the aquifer. Denaturing gradient gel electrophoresis analysis of aquifer water samples using principal components analyses indicated that the microbial community composition was spatially variable, and denaturing gradient gel electrophoresis sequence analysis revealed that bacteria belonging to the genera Acidovorax , Rhodobacter , and Sulfuricurvum were common throughout the aquifer. Shannon’s richness (H′) and Pielou’s evenness (J′) indices revealed a varied microbial diversity (H′ = 1.488–2.274) and an even distribution of microbial communities within the aquifer (J′ = 0.811–0.917). Overall, these analyses revealed that the aquifer’s microbial community varied spatially in terms of composition, richness, and metabolic activity. Such information may facilitate the diagnosis, prevention, and management of fouling.

Delftia acidovorans has been associated with a number of serious infections, including bacteremia, empyema, bacterial endocarditis, and ocular and urinary tract infections. It has also been linked with a variety of surface-associated nosocomial infections. Biofilm-forming antimicrobial-resistant D. acidovorans strains have also been isolated, including ones displaying resistance to the common broad-spectrum agent chlorhexidine. The mechanisms of chlorhexidine resistance in D. acidovorans are not known; hence, a chlorhexidine-susceptible mutant of the tolerant wild-type strain was obtained using transposon mutagenesis, and the proteome and ultrastructural changes of both strains were compared under chlorhexidine challenge., Protein expression and fatty acid profiles of biofilm cells of chlorhexidine-tolerant Delftia acidovorans (MIC = 15 µg/ml) and its chlorhexidine-susceptible mutant (MIC = 1 µg/ml) were investigated. The chlorhexidine-susceptible mutant (MT51) was derived from the parental strain (WT15) using Tn5 transposon mutagenesis. The disrupted gene was identified as tolQ, a component of the tolQRAB gene cluster known to be involved in outer membrane stability. Proteomic responses of biofilm cells were compared by differential in-gel electrophoresis following exposure to chlorhexidine at sub-MIC (10 µg/ml) and above-MIC (30 µg/ml) concentrations. Numerous changes in protein abundance were observed in biofilm cells following chlorhexidine exposure, suggesting that molecular changes occurred during adaptation to chlorhexidine. Forty proteins showing significant differences (≥1.5-fold; P < 0.05) were identified by mass spectrometry and were associated with various functions, including amino acid and lipid biosynthesis, protein translation, energy metabolism, and stress-related functions (e.g., GroEL, aspartyl/glutamyl-tRNA amidotransferase, elongation factor Tu, Clp protease, and hydroxymyristoyl-ACP dehydratase). Several proteins involved in fatty acid synthesis were affected by chlorhexidine, in agreement with fatty acid analysis, wherein chlorhexidine-induced shifts in the fatty acid profile were observed in the chlorhexidine-tolerant cells, primarily the cyclic fatty acids. Transmission electron microscopy revealed more prominent changes in the cell envelope of chlorhexidine-susceptible MT51 cells. This study suggests that multiple mechanisms involving both the cell envelope (and likely TolQ) and panmetabolic regulation play roles in chlorhexidine tolerance in D. acidovorans. IMPORTANCE Delftia acidovorans has been associated with a number of serious infections, including bacteremia, empyema, bacterial endocarditis, and ocular and urinary tract infections. It has also been linked with a variety of surface-associated nosocomial infections. Biofilm-forming antimicrobial-resistant D. acidovorans strains have also been isolated, including ones displaying resistance to the common broad-spectrum agent chlorhexidine. The mechanisms of chlorhexidine resistance in D. acidovorans are not known; hence, a chlorhexidine-susceptible mutant of the tolerant wild-type strain was obtained using transposon mutagenesis, and the proteome and ultrastructural changes of both strains were compared under chlorhexidine challenge.

In this study, we tested the antimicrobial activity of three metal nanoparticles (NPs), ZnO, MgO, and CaO NPs, against Salmonella enterica serovar Enteritidis in liquid medium and on solid surfaces. Out of the three tested metal NPs, ZnO NPs exhibited the most significant antimicrobial effect both in liquid medium and when embedded on solid surfaces. Therefore, we focused on revealing the mechanisms of surface-associated ZnO biocidal activity. Using the global proteome approach, we report that a great majority (79%) of the altered proteins in biofilms formed by Salmonella enterica serovar Enteritidis were downregulated, whereas a much smaller fraction (21%) of proteins were upregulated. Intriguingly, all downregulated proteins were enzymes involved in a wide range of the central metabolic pathways, including translation; amino acid biosynthetic pathways; nucleobase, nucleoside, and nucleotide biosynthetic processes; ATP synthesis-coupled proton transport; the pentose phosphate shunt; and carboxylic acid metabolic processes, indicating that ZnO NPs exert a panmetabolic toxic effect on this prokaryotic organism. In addition to their panmetabolic toxicity, ZnO NPs induced profound changes in cell envelope morphology, imposing additional necrotic effects and triggering the envelope stress response of Salmonella serovar Enteritidis. The envelope stress response effect activated periplasmic chaperones and proteases, transenvelope complexes, and regulators, thereby facilitating protection of this prokaryotic organism against ZnO NPs.

The emergence of multidrug resistance in bacteria has reached alarming levels. To solve this growing problem, discovery of novel cellular targets or pathways important for antimicrobial resistance is urgently needed. In this study, we explored how the alternative sigma factor, RpoE, protects Escherichia coli O157 against the toxic effects of the polycationic antimicrobial agent, chlorhexidine (CHX). Susceptibility of this organism to CHX was found to directly correlate to the growth rate, with the faster replicating wild-type being more susceptible to CHX than its more slowly replicating ΔrpoE O157 mutant. Once the wild-type and rpoE mutant strains had undergone growth arrest (entered the stationary growth phase), their resistance to CHX became entirely dependent on the functionality of RpoE. The RpoE regulon plays a critical role in maintaining the integrity of the asymmetric lipid bilayer of E. coli, thereby preventing the intracellular accumulation of CHX. Finally, using a single-cell, high-resolution, synchrotron-based approach, we discovered a subpopulation of the rpoE mutant strain with no detectable intracellular CHX, a predominant characteristic of the wild-type CHX-resistant population. This finding reveals a role of phenotypic heterogeneity in antimicrobial resistance.