Metagenomic analysis of heavy metal-contaminated soils reveals distinct clades with adaptive features

Abstract

Heavy metal pollution poses a serious threat to soil, water, and the atmospheric environment. Many microbes sustain and respond to the metal stress, and the mechanisms involved in these processes remain unclear. The metagenomics and metatranscriptomics approaches were applied to study the structure and function of eukaryotic microbial communities in heavy metal-contaminated soils of two geographic locations situated in different climatic regions. To achieve this, amplicons of the hypervariable V4 region of 18S rDNA and cDNA synthesized from 18S rRNA extracted from these soils were generated and sequenced through paired-end sequencing chemistry on the Illumina-MiSeq platform. The NGS dataset processed by the Mothur pipeline and analyzed by Parallel-Meta 3 pipeline illustrated the presence of all the major eukaryotic phyla. Taxa diversity and community structure of micro-eukaryotes within and between the samples from two locations were compared. Clustering, heatmap, and PCA analysis supported the variation in taxonomic diversity and community structure in the datasets of these two sites. Analysis of taxa abundance in both sites identified marker organisms for the further characterization of such types of environments. A functional metatranscriptomics study revealed the identification of various expressed eukaryotic genes, which are involved in metal tolerance. These metal-tolerant gene families were phylogenetically related to the different eukaryotic lineages reported in the metagenomic analysis. Hence, this approach could be widely applied in microbial ecology to understand the role of active microbes in such specific environmental conditions.