Long- and short-term effects of mercury pollution on the soil microbiome

Despite the toxicity of mercury (Hg) for organisms in the environment, little is known on its impact on the soil microbiome, especially its persisting effect. Here, we assessed the effects of a long-term contamination of Hg in soils on the bacterial and fungal communities along a gradient of contamination from no to high contamination. Short-term reactions (30 days) of the microbial communities in these soils having different levels of historic Hg contamination were further evaluated in microcosm experiments where soils were either spiked with dissolved HgCl2 or not. Results show a strong impact of a long-term Hg contamination on both bacterial and fungal community structures, diversities and activities (basal respiration and growth rates). In contrast, no short-term effects of Hg was observed on the microbial community structures and activities. Indicator species analysis showed that taxa from the Chthoniobacteraceae (bacteria), Leptodontidium sp. (fungi) and Trichosporon sp. (fungi) were strongly associated with high Hg contaminated soils, implying they possess capabilities to tolerate Hg in soils.