Stress response characteristics of indigenous microorganisms in aromatic-hydrocarbons-contaminated groundwater in the cold regions of Northeast China

Abstract

The resistance mechanism of microbial communities in contaminated groundwater under combined stresses of aromatic hydrocarbons (AHs), NH4+, and Fe–Mn exceeding standard levels was studied in an abandoned oil depot in Northeast China. The response of environmental parameters and microbial communities under different pollution levels in the study area was discussed, and microscopic experiments were conducted using background groundwater with different AHs concentrations. The results showed that indigenous microbial community were significantly affected by environmental factors, including pH, TH, CODMn, TFe, Cr (VI), NH4+, NO3-, and SO42-. AHs likely had a limited influence on microbial communities, mainly causing indirect changes in the microbial community structure by altering the electron donor/acceptor (mainly Fe, Mn, NO3-, NO2-, NH4+, and SO42-) content in groundwater, and there was no linear effect of AHs content on the microbial community. In low- and medium-AHs-contaminated groundwater, the microbial diversity increased, whereas high AHs contents decreased the diversity of the microbial community. The microbial community had the strongest ability to metabolize AHs in the medium-AHs-contaminated groundwater. In the high-AHs-contaminated groundwater, microbial communities mainly degraded AHs through a complex co-metabolic mechanism due to the inhibitory effect caused by the high concentration of AHs, whereas in low-AHs-contaminated groundwater, microbial communities mainly caused a mutual transformation of inorganic electron donors/acceptors (mainly including N, S), and the microbial community’s ability to metabolize AHs was weak. In the high-AHs-contaminated groundwater, the microbial community resisted the inhibitory effect of AHs mainly via a series of resistance mechanisms, such as regulating their life processes, avoiding unfavorable environments, and enhancing their feedback to the external environment under high-AHs-contaminated conditions.