Biodegradation of Aromatic Hydrocarbons in an Extremely Acidic Environment

Abstract

The potential for biodegradation of aromatic hydrocarbons was evaluated in soil samples recovered along gradients of both contaminant levels and pH values existing downstream of a long-term coal pile storage basin. pH values for areas greatly impacted by runoff from the storage basin were 2.0. Even at such a reduced pH, the indigenous microbial community was metabolically active, showing the ability to oxidize more than 40% of the parent hydrocarbons, naphthalene and toluene, to carbon dioxide and water. Treatment of the soil samples with cycloheximide inhibited mineralization of the aromatic substrates. DNA hybridization analysis indicated that whole-community nucleic acids recovered from these samples did not hybridize with genes, such asnahA, nahG, nahH,todC1C2, and tomA, that encode common enzymes from neutrophilic bacteria. Since these data suggested that the degradation of aromatic compounds may involve a microbial consortium instead of individual acidophilic bacteria, experiments using microorganisms isolated from these samples were initiated. While no defined mixed cultures were able to evolve14CO2 from labeled substrates in these mineralization experiments, an undefined mixed culture including a fungus, a yeast, and several bacteria successfully metabolized approximately 27% of supplied naphthalene after 1 week. This study shows that biodegradation of aromatic hydrocarbons can occur in environments with extremely low pH values.

Acidophilic microbial communities associated with a natural, biodegraded hydrocarbon seepage

“…Interestingly, Acidiphilium sequences were also found to dominate microbial communities in a hexadecane mineralizing soil-sand mixture derived from a petroleum seep in Yellowstone Park (Hamamura et al 2005). Biodegradation of aromatic hydrocarbons under acidic conditions has previously been observed in a man-made long-term coal pile storage basin (Stapleton et al 1998). In this case, the activity of eukaryotic micro-organisms was essential for aromatic hydrocarbon degradation in the pH 2AE0 basin.…”

Molecular identification of species comprising an unusual biofilm from a groundwater treatment plant

“…Acidophilic, heterotrophic Alphaproteobacteria such as Acidocella occur world-wide in natural hydrocarbon seeps, presumably utilizing the hydrocarbon as an energy and carbon source (Roling et al, 2006). Acidocella and Pichia were isolated from the same PAH-contaminated soil, in a study that concluded that an undefined consortium of yeasts, filamentous fungi and bacteria was responsible for degradation of aromatic hydrocarbons (Stapleton et al, 1998). Whether the biofilm members we have described are also able to mineralize organic pollutants in the groundwater is currently unknown.…”

“…Acidocella was originally described as inhabiting acidic aquatic habitats (Kishimoto et al, 1995) and is found as planktonic cells in acid mining lakes (Johnson et al, 2001;Wenderoth & Abraham, 2005). Pichia relatives can be recovered from acidic lakes (Gadhano & Sampaio, 2006), and Acidocella and Pichia have previously been reported as occurring together in highly acidic environments, although not as an obvious biofilm (Stapleton et al, 1998). Trichoderma asperellum has not been recorded from groundwater, but is known to grow at pH 2.2 (Kawai et al, 2000), and both Trichoderma and Candida have been recorded in sandstone, which is the bedrock type in the area (Burford et al, 2003).…”

Literature overview: Microbial metabolism of high molecular weight polycyclic aromatic hydrocarbons

“…Some PAH degraders are extremophiles, which are microorganisms that can thrive in and withstand extreme environmental conditions (Tango & Islam, 2002). Examples include Halomonas aromativorans (Garcia et al, 2005), Halomonas organivorans (Garcia et al, 2004), and Acidocella-related Strain SRS (Stapleton et al, 1998), which can metabolize salicylate. Thermus brockii (Feitkenhauer et al, 2003) and Mycobacterium sp.…”