The long and short term response of soil microbial communities to heavy metals in cultivated grassland

At sites contaminated with heavy metals, the composition and activity of microbial communities are influenced by stress factors one of which is the content and character of organic matter. Actinobacteria contribute to breakdown of organic matter and survive in heavy metal contaminated conditions because they possess efflux resistances enabling cell detoxification. The aim of the study was to show how organic matter decomposition is affected by heavy metal contamination in Actinobacteria.We selected two sites differing in long-term contamination by cadmium (L low, H high contamination). We assessed the changes in respiration after addition of cadmium and two organic substrates, cellobiose and straw using OxiTop system. We assessed quantity of actinobacteria by qPCR, diversity of cellobiohydrolase by specific primers, and bacterial diversity by Illumina sequencing. The addition of cadmium did not have any effect on respiration but in the cellobiose-cadmium treatment. The addition of organic substrate did not influence the quantity of actinobacteria but in the cadmium-cellobiose treatment at H site. Sequences of cbh gene (coding for cellobiohydrolase) differed significantly (Libshuff) between the sites H and L, both untreated and in the straw-cadmium threatment. The two sites differed in actinobacteria community composition after addition of straw, Micrococcaceae increased at both sites, Nocardiaceae and Cellulomonadaceae increased at H site, and Thermomonosporaceae increased at L site. In conclusion, the microbial communities at site with low contamination seemed to be more resilient being less affected after additions of organic substrates.