Meta‐Transcriptomes From Microcosms From a Cr Impacted Soil Provides Insights Into the Metabolic Response of the Microbial Populations to Acetate Stimulation

Environmental contamination by Cr(VI) leaching from chromite ore processing residue (COPR) legacy disposal sites can posea threat to human health. Under iron-reducing conditions, microbial activity can convert mobile and toxic Cr(VI) to less mobileand less toxic Cr(III); however, COPR waste is a very hostile environment for microbial life. Microcosms using soil from beneatha COPR disposal site were challenged with Cr(VI) with and without acetate to stimulate microbial metabolism. Geochemistryshowed that when the microbial populations were reducing iron, Cr(VI) was also reduced, and 16S rRNA gene sequencingshowed that the community composition evolved over the course of the experiment. Meta-transcriptome data revealed ~3% oftranscripts were differentially regulated (p = 0.01) between the acetate amended and unamended systems, with twice as manytranscripts downregulated by acetate. Gene ontology (GO) terms for processes involving the cell wall, cell periphery, plasmamembrane and encapsulating structures as well as catabolic processes, especially carbohydrate metabolism, were significantlyenriched in the unamended microcosm meta-transcriptome. Transcripts for alternative sigma (σ) factors and anti- σ factors wereprominent among the differentially regulated genes. The study provides insight into how the provision of acetate shapes meta-bolic processes and life history strategies in an alkaline Cr(VI) impacted environment.