Linking microbial community and catabolic gene structures during the adaptation of three contaminated soils under continuous long term pollutant stress.

Three types of contaminated soil from three geographically different areas were subjected to a constant supply of benzene or benzene/toluene/ethylbenzene/xylenes for a period of 3 months. Different to the soil from Brazil (BRA) and Switzerland (SUI), the Czech Republic (CZE) soil which was previously subjected to intensive in-situ bioremediation displayed only negligible changes in community structure. BRA and SUI soil samples showed a clear succession of phylotypes. A rapid response to benzene stress was observed whereas the response to BTEX pollution was significantly slower. After extended incubation, actinobacterial phylotypes were increasing in relative abundance, indicating their superior fitness to pollution stress. Commonalities, but also differences in the phylotypes were observed. Catabolic gene surveys confirmed the enrichment of actinobacteria by identifying the increase of actinobacterial genes involved in the degradation of pollutants. Proteobacterial phylotypes were increasing in relative abundance in SUI microcosms after short-term stress with benzene, where catabolic gene surveys indicated metabolic routes enriched. Interestingly, CZE soil, despite staying constant in community structure, showed a change in the metabolic net, indicating that a highly adapted community has been enriched, which had to adapt its gene pool to meet novel challenges