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Three toluene-degrading microbial consortia were enriched under sulphate-reducing conditions from different zones of a benzene, toluene, ethylbenzene and xylenes (BTEX) plume of two connected contaminated aquifers. Two cultures were obtained from a weakly contaminated zone of the lower aquifer, while one culture originated from the highly contaminated upper aquifer. We hypothesised that the different habitat characteristics are reflected by distinct degrader populations. Degradation of toluene with concomitant production of sulphide was demonstrated in laboratory microcosms and the enrichment cultures were phylogenetically characterised. The benzylsuccinate synthase alpha-subunit (bssA) marker gene, encoding the enzyme initiating anaerobic toluene degradation, was targeted to characterise the catabolic diversity within the enrichment cultures. It was shown that the hydrogeochemical parameters in the different zones of the plume determined the microbial composition of the enrichment cultures. Both enrichment cultures from the weakly contaminated zone were of a very similar composition, dominated by Deltaproteobacteria with the Desulfobulbaceae (a Desulfopila-related phylotype) as key players. Two different bssA sequence types were found, which were both affiliated to genes from sulphate-reducing Deltaproteobacteria. In contrast, the enrichment culture from the highly contaminated zone was dominated by Clostridia with a Desulfosporosinus-related phylotype as presumed key player. A distinct bssA sequence type with high similarity to other recently detected sequences from clostridial toluene degraders was dominant in this culture. This work contributes to our understanding of the niche partitioning between degrader populations in distinct compartments of BTEX-contaminated aquifers.

Microbial communities from three Argentinean saline soils were extracted and tested for their ability to degrade diesel fuel in liquid culture at salinities between 0% and 25%. In each case, the degradation process was continuously monitored by measuring oxygen consumption. Two communities (CR1 and CR2) showed nearly equal degrees of degradation across a salinity range of 0%-10% (the former degrading about 63% of the diesel fuel and the latter about 70% after 53 and 80 d, respectively). Furthermore, the degree of degradation was not significantly lower in the presence of 17.5% salt (58% and 65% degraded, respectively). A third community (El Zorro) showed a maximum turnover at 5% salt (79% diesel fuel degraded) and significant degradation (66%) at a salinity of 10%. However, the degree of degradation by this community clearly dropped at 0% and 15% salt. None of the communities were able to degrade diesel fuel in the presence of 25% salt, but the living cell counts showed that components of the microbial population survived the long-term exposure. The surviving portion is obviously sufficient to allow substantial restoration of the original community, as verified by the BIOLOG method. Isolates of the CR1 community were identified as members of the genera Cellulomonas, Bacillus, Dietzia, and Halomonas. In light of our investigations, the bioremediation of contaminated saline soils should be quite possible if the salinity of the soil water is lower than 15% or if it is reduced below this limit by the addition of water.