Marine crude-oil biodegradation: a central role for interspecies interactions

The marine environment is highly susceptible to pollution by petroleum, and so it is important to understand how microorganisms degrade hydrocarbons, and thereby mitigate ecosystem damage. Our understanding about the ecology, physiology, biochemistry and genetics of oil-degrading bacteria and fungi has increased greatly in recent decades; however, individual populations of microbes do not function alone in nature. The diverse array of hydrocarbons present in crude oil requires resource partitioning by microbial populations, and microbial modification of oil components and the surrounding environment will lead to temporal succession. But even when just one type of hydrocarbon is present, a network of direct and indirect interactions within and between species is observed. In this review we consider competition for resources, but focus on some of the key cooperative interactions: consumption of metabolites, biosurfactant production, provision of oxygen and fixed nitrogen. The emphasis is largely on aerobic processes, and especially interactions between bacteria, fungi and microalgae. The self-construction of a functioning community is central to microbial success, and learning how such " microbial modules" interact will be pivotal to enhancing biotechnological processes, including the bioremediation of hydrocarbons. © 2012 McGenity et al.; licensee BioMed Central Ltd

Diamondoids are not forever: microbial biotransformation of diamondoid carboxylic acids

Oil sands process‐affected waters (OSPW) contain persistent, toxic naphthenic acids (NAs), including the abundant yet little‐studied diamondoid carboxylic acids. Therefore, we investigated the aerobic microbial biotransformation of two of the most abundant, chronically toxic and environmentally relevant diamondoid carboxylic acids: adamantane‐1‐carboxylic acid (A1CA) and 3‐ethyl adamantane carboxylic acid (3EA). We inoculated into minimal salts media with diamondoid carboxylic acids as sole carbon and energy source two samples: (i) a surface water sample (designated TPW) collected from a test pit from the Mildred Lake Settling Basin and (ii) a water sample (designated 2 m) collected at a water depth of 2 m from a tailings pond. By day 33, in TPW enrichments, 71% of A1CA and 50% of 3EA was transformed, with 50% reduction in EC20 toxicity. Similar results were found for 2 m enrichments. Biotransformation of A1CA and 3EA resulted in the production of two metabolites, tentatively identified as 2‐hydroxyadamantane‐1‐carboxylic acid and 3‐ethyladamantane‐2‐ol respectively. Accumulation of both metabolites was less than the loss of the parent compound, indicating that they would have continued to be transformed beyond 33 days and not accumulate as dead‐end metabolites. There were shifts in bacterial community composition during biotransformation, with Pseudomonas species, especially P. stutzeri, dominating enrichments irrespective of the diamondoid carboxylic acid. In conclusion, we demonstrated the microbial biotransformation of two diamondoid carboxylic acids, which has potential application for their removal and detoxification from vast OSPW that are a major environmental threat

Exploring the capacity for anaerobic biodegradation of polycyclic aromatic hydrocarbons and naphthenic acids by microbes from oil-sands-process-affected waters

Both polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs) are natural components of fossil fuels, but they are also widespread toxic and environmentally persistent pollutants. They are the major cause of environmental toxicity in oil-sands-process waters (OSPW). This study aimed to investigate the anaerobic biodegradation of the PAHs pyrene and 2-methylnaphthalene, and the NAs adamantane-1-carboxylic acid and a "natural" NA mixture (i.e., acid-extractable NAs from OSPW) under sulfate-reducing and methanogenic conditions by a microbial community derived from an oil sands tailings pond. Using gas-chromatography mass spectrometry (GC-MS), the rate of biodegradation was measured in relation to changes in bacterial community composition. Only 2-methylnaphthalene was significantly degraded after 260 days, with significantly more degradation under sulfate-reducing (40%) than methanogenic conditions (25%). During 2-methylnaphthalene biodegradation, a major metabolite was produced and tentatively identified as 2-naphthoic acid. Denaturing gradient gel electrophoresis (DGGE) demonstrated an increase in intensity of bands during the anaerobic biodegradation of 2-methylnaphalene, which derived from species of the genera Fusibacter, Alkaliphilus, Desulfobacterium, Variovorax, Thaurea, and Hydrogenophaga. Despite the biodegradation of 2-methylnaphthalene, this study demonstrates that, under anaerobic conditions, NAs and high-molecular-weight PAHs are the predominant molecules likely to persist in OSPW. Therefore alternative remediation strategies are required