Joe Lemire

Harnessing oil sands microbial communities for use in ex situ naphthenic acid bioremediation.

The caustic hot water extraction process used to release bitumen from the Alberta oil sands generates large volumes of tailings waste, or oil sands process water (OSPW). OSPW contains several components of environmental concern including diluents, polyaromatic hydrocarbons, heavy metals, and naphthenic acids (NAs); the latter are of particular concern as they are acutely toxic to aquatic organisms and mammals. Studies have demonstrated that the naturally occurring OSPW bacteria are capable of metabolizing the NAs. However, this in situ process takes place over hundreds of years, and is incomplete, leaving a recalcitrant fraction of NAs intact. In this study we explore options for recovering and harnessing the naturally occurring OSPW bacteria for potential future use in an aerobic ex situ OSPW treatment system. Here we evaluate our recovered microbes on their ability to degrade two model NAs, cyclohexane carboxylic acid and cyclohexane acetic acid. Using OSPW as a source for a bacterial inoculum, we were able to compare single and multispecies OSPW cultures, grown as either a biofilm, or as a planktonic suspension. Furthermore, we examined the effect of available nutrients on the ability of these cultures to degrade NAs. All biofilms were grown using the Calgary Biofilm Device. GC-MS, and GC-FID reveal that multispecies biofilm and planktonic cultures are each capable of degrading both NAs; a trait not observed for single species cultures. Moreover, complementary carbon sources have a tangible effect on the ability of the cultures to initiate the degradation of the NAs.

Silver oxynitrate: An Unexplored Silver Compound with Antimicrobial and Antibiofilm Activity

ABSTRACT Historically it has been accepted, and recent research has established, that silver (Ag) is an efficacious antimicrobial agent. A dwindling pipeline of new antibiotics, combined with an increase in the number of antibiotic-resistant infections, is bringing Ag to the fore as a therapeutic compound to treat infectious diseases. Currently, many formulations of Ag are being deployed for commercial and medical purposes, with various degrees of effectiveness at killing microbial cells. Here, we evaluated the antimicrobial and antibiofilm capacity of our lead compound, silver oxynitrate [Ag(Ag3O4)2NO3 or Ag7NO11], against other metal compounds with documented antimicrobial activity, including Ag2SO4, AgNO3, silver sulfadiazine (AgSD), AgO, Ag2O, and CuSO4. Our findings reveal that Ag7NO11 eradicates biofilm and planktonic populations of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, uropathogenic Escherichia coli (UPEC), fluoroquinolone-resistant Pseudomonas aeruginosa (FQRP), and methicillin-resistant Staphylococcus aureus (MRSA) at lower concentrations than those of the other tested metal salts. Altogether, our results demonstrate that Ag7NO11 has an enhanced efficacy for the treatment of biofilm-forming pathogens.

Metabolic defence against oxidative stress: the road less travelled so far

Bacteria have survived, and many have thrived, since antiquity in the presence of the highly‐reactive chalcogen—oxygen (O2). They are known to evoke intricate strategies to defend themselves from the reactive by‐products of oxygen—reactive oxygen species (ROS). Many of these detoxifying mechanisms have been extensively characterized; superoxide dismutase, catalases, alkyl hydroperoxide reductase and the glutathione (GSH)‐cycling system are responsible for neutralizing specific ROS. Meanwhile, a pool of NADPH—the reductive engine of many ROS‐combating enzymes—is maintained by metabolic enzymes including, but not exclusively, glucose‐6 phosphate dehydrogenase (G6PDH) and NADP‐dependent isocitrate dehydrogenase (ICDH‐NADP). So, it is not surprising that evidence continues to emerge demonstrating the pivotal role metabolism plays in mitigating ROS toxicity. Stemming from its ability to concurrently decrease the production of the pro‐oxidative metabolite, NADH, while augmenting the antioxidative metabolite, NADPH, metabolism is the fulcrum of cellular redox potential. In this review, we will discuss the mounting evidence positioning metabolism and metabolic shifts observed during oxidative stress, as critical strategies microbes utilize to thrive in environments that are rife with ROS. The contribution of ketoacids—moieties capable of non‐enzymatic decarboxylation in the presence of oxidants—as ROS scavengers will be elaborated alongside the metabolic pathways responsible for their homeostases. Further, the signalling role of the carboxylic acids generated following the ketoacid‐mediated detoxification of the ROS will be commented on within the context of oxidative stress.

The efficacy of different anti-microbial metals at preventing the formation of, and eradicating bacterial biofilms of pathogenic indicator strains

The emergence of multidrug-resistant pathogens and the prevalence of biofilm-related infections have generated a demand for alternative anti-microbial therapies. Metals have not been explored in adequate detail for their capacity to combat infectious disease. Metal compounds can now be found in textiles, medical devices and disinfectants—yet, we know little about their efficacy against specific pathogens. To help fill this knowledge gap, we report on the anti-microbial and antibiofilm activity of seven metals: silver, copper, titanium, gallium, nickel, aluminum and zinc against three bacterial strains, Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. To evaluate the capacity of metal ions to prevent the growth of, and eradicate biofilms and planktonic cells, bacterial cultures were inoculated in the Calgary Biofilm Device (minimal biofilm eradication concentration) in the presence of the metal salts. Copper, gallium and titanium were capable of preventing planktonic and biofilm growth, and eradicating established biofilms of all tested strains. Further, we observed that the efficacies of the other tested metal salts displayed variable efficacy against the tested strains. Further, contrary to the enhanced resistance anticipated from bacterial biofilms, particular metal salts were observed to be more effective against biofilm communities versus planktonic cells. In this study, we have demonstrated that the identity of the bacterial strain must be considered before treatment with a particular metal ion. Consequent to the use of metal ions as anti-microbial agents to fight multidrug-resistant and biofilm-related infections increases, we must aim for more selective deployment in a given infectious setting.

Silver oxynitrate – an efficacious compound for the prevention and eradication of dual-species biofilms

Abstract Preventing and eradicating biofilms remains a challenge in clinical and industrial settings. Recently, the present authors demonstrated that silver oxynitrate (Ag7NO11) prevented and eradicated single-species planktonic and biofilm populations of numerous microbes at lower concentrations than other silver (Ag) compounds. Here, the antimicrobial and anti-biofilm efficacy of Ag7NO11 is elaborated by testing its in vitro activity against combinations of dual-species, planktonic and biofilm populations of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. As further evidence emerges that multispecies bacterial communities are more common in the environment than their single-species counterparts, this study reinforces the diverse applicability of the minimal biofilm eradication concentration (MBEC™) assay for testing antimicrobial compounds against biofilms. Furthermore, this study demonstrated that Ag7NO11 had enhanced antimicrobial and anti-biofilm activity compared to copper sulfate (CuSO4) and silver nitrate (AgNO3) against the tested bacterial species.

Evaluating the Metal Tolerance Capacity of Microbial Communities Isolated from Alberta Oil Sands Process Water.

Anthropogenic activities have resulted in the intensified use of water resources. For example, open pit bitumen extraction by Canada’s oil sands operations uses an estimated volume of three barrels of water for every barrel of oil produced. The waste tailings–oil sands process water (OSPW)–are stored in holding ponds, and present an environmental concern as they are comprised of residual hydrocarbons and metals. Following the hypothesis that endogenous OSPW microbial communities have an enhanced tolerance to heavy metals, we tested the capacity of planktonic and biofilm populations from OSPW to withstand metal ion challenges, using Cupriavidus metallidurans, a known metal-resistant organism, for comparison. The toxicity of the metals toward biofilm and planktonic bacterial populations was determined by measuring the minimum biofilm inhibitory concentrations (MBICs) and planktonic minimum inhibitory concentrations (MICs) using the MBEC ™ assay. We observed that the OSPW community and C. metallidurans had similar tolerances to 22 different metals. While thiophillic elements (Te, Ag, Cd, Ni) were found to be most toxic, the OSPW consortia demonstrated higher tolerance to metals reported in tailings ponds (Al, Fe, Mo, Pb). Metal toxicity correlated with a number of physicochemical characteristics of the metals. Parameters reflecting metal-ligand affinities showed fewer and weaker correlations for the community compared to C. metallidurans, suggesting that the OSPW consortia may have developed tolerance mechanisms toward metals present in their environment.

Using a Chemical Genetic Screen to Enhance Our Understanding of the Antibacterial Properties of Silver

It is essential to understand the mechanisms by which a toxicant is capable of poisoning the bacterial cell. The mechanism of action of many biocides and toxins, including numerous ubiquitous compounds, is not fully understood. For example, despite the widespread clinical and commercial use of silver (Ag), the mechanisms describing how this metal poisons bacterial cells remains incomplete. To advance our understanding surrounding the antimicrobial action of Ag, we performed a chemical genetic screen of a mutant library of Escherichia coli—the Keio collection, in order to identify Ag sensitive or resistant deletion strains. Indeed, our findings corroborate many previously established mechanisms that describe the antibacterial effects of Ag, such as the disruption of iron-sulfur clusters containing proteins and certain cellular redox enzymes. However, the data presented here demonstrates that the activity of Ag within the bacterial cell is more extensive, encompassing genes involved in cell wall maintenance, quinone metabolism and sulfur assimilation. Altogether, this study provides further insight into the antimicrobial mechanism of Ag and the physiological adaption of E. coli to this metal.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications

Abstract Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS – nitric oxide (·NO) and peroxynitrite (ONOO−) – play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites – α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.