Degradation of a benzene-toluene mixture by hydrocarbon-adapted bacterial communities

Abstract

We examined the rate of degradation of a benzene-toluene mixture in aerobic microcosms prepared with samples of an aquifer that lies below a petrochemical plant (SIReN, UK). Five samples exposed to different concentrations of benzene (from 0.6 to 317 mg l(-1)) were used. Fast degradation (approx. 1-6 mg l(-1) day(-1)) of both contaminants was observed in all groundwater samples and complete degradation was recorded by the seventh day except for one sample. We also identified the microbial community in each of the samples by culture-independent techniques. Two of the less impacted samples harbour the aerobic benzene degrader Pseudomonas fluorescens, while Acidovorax and Arthrobacter spp. were found in the most polluted sample and are consistent with the population observed in situ. Hydrogenophaga was found in the deepest sample while Rhodoferax spp. were recovered in an alkaline sample (pH 8.4) and may also be implicated in benzene degradation. Time series analysis shows that each of the samples has a different community but they remain stable over the degradation period. This study provides new information on a well not previously studied (no. 309s) and confirms that adapted communities have the ability to degrade hydrocarbon mixtures and could be used in further bioaugmentation approaches in contaminated sites.

Fig. 1

Outline of the site SIReN, with general direction of the groundwater flow and location of wells sampled. All wells have an official name used in this study and in official reports (e.g. Jones et al. 2001), but in some papers (e.g. Fahy et al. 2005, 2006), a shorter code has been used (indicated in parentheses here). For well clusters at the same location, the relative depth is indicated in the text by s (shallow), i (intermediate) or d (deep) following the location name. For example, W18i analysed in this study was called Pi in (Fahy et al. 2005); it lies below W18s and above W18d

Fig. 2

Degradation of benzene–toluene mixtures by aerobic microcosms of groundwater samples. Benzene (∎), toluene (▲), sterile controls of benzene (☐) and toluene (∆). The presented data are the means of triplicate experiments; error bars represent standard deviation of triplicates

Fig. 3

DGGE gel showing the bacterial communities over time in microcosms of groundwater samples in wells 309d, DW3s, W18i, 309s and 308i inoculated with a mixture of benzene and toluene. Closest relatives of band 1: Hydrogenophaga flava, bands 3 + 4: Pseudomonas fluorescens Pf-5, bands 5 + 6: Pseudomonas mephitica ATCC, bands 7 + 8: Acidovorax sp. A-07-20, band 9: Arthrobacter sp. 14III, band 10: Pseudomonas fluorescens P69, band 11: Pseudomonas syringae B728a, bands 12 + 13: Rhodoferax antarcticus, band 14: Methylobacter sp. SV96

Fig. 4

Relationship between the composition of bacterial communities from five groundwater samples 309d, DW3s, W18i, 309s, 308i over 6 days. Relative depths of wells are indicated by: d deep, i intermediate, s shallow The dendrogram was created using Bray Curtis similarity which treats the data on a presence/absence basis and equates to the Sorensen coefficient