Cadmium stress triggers significant metabolic reprogramming in Enterococcus faecium CX 2–6

Heavy metal pollutions in the soils are increasingly threatening the global crop and food production. Using plant associated bacteria to remediate heavy metal contamination is a promising approach. We have isolated a cadmium (Cd) resistant Enterococcus faecium strain CX 2-6 from a heavy metal contaminated farmland. We have shown that: (i) CX 2-6 can tolerate cadmium (Cd) with a slower growth rate; (ii) The CX 2-6 complete genome is fully assembled using PacBio long reads; (iii) Differential expression analysis found 47% of CX 2-6 genes are significantly affected by Cd treatment and form three gene groups with distinct expression profiles; (iv) Differentially expressed genes (DEGs) form physically linked gene clusters in the CX 2-6 genome, and one of the gene clusters corresponds to a prophage that is unique to CX 2-6 and is strongly activated when Cd concentration is higher; (v) A majority of DEGs responding to Cd treatment are present in the core genome; and (vi) 55 noncoding RNA genes are identified and 49 of them are DEGs responding to cadmium stress. Our pan-genome analysis and comparative RNA-seq data analysis has significantly improved our understanding of the metabolic reprogramming of E. faecium CX 2-6 under Cd stress.