A novel 1,2-dichloroethane degrading Ancylobacter in a consortium for enhanced aerobic bioremediation

Abstract

1,2-dichloroethane (1,2-DCA) is a toxic chlorinated hydrocarbon and frequent groundwater contaminant. 1,2-DCA can be biodegraded by specialized aerobic and anaerobic bacteria. The aerobic hydrolytic dechlorination is performed by few known bacteria, mainly affiliated to two Xanthobacteriaceae genera, Xanthobacter and Ancylobacter, isolated from different geographic locations. These isolates carry an identical dhlA gene, encoding for the key enzyme haloalkane dehalogenase. The aim of this study was to isolate novel 1,2-DCA degrading bacteria to be exploited in enhanced bioremediation strategies. A dechlorinating enrichment culture obtained from 1,2-DCA contaminated groundwater was streaked on solid mineral medium amended with 1,2-DCA as sole carbon source for bacterial isolation. A stable consortium dominated by Ancylobacter followed by few other genera was obtained, as revealed by IonTorrent 16S rRNA gene sequencing. Gas Chromatography-Mass Spectrometry revealed the consortium degraded 1000 ppm 1,2-DCA in three days. Ancylobacter was identified as the main degrader by comparing dhlA and Ancylobacter 16S rRNA genes abundance over time by qPCR. The role of other consortium members is still under study. A dhlA gene, identical to that of all other known hydrolytic 1,2-DCA-degraders, usually plasmid-borne, was detected and located on Ancylobacter chromosome by Whole Genome Sequencing, as well as the other genes involved in 1,2-DCA hydrolytic dechlorination. Transposase genes flanking catabolic genes confirm that horizontal gene transfer can spread the 1,2-DCA degrading phenotype. Ancylobacter whole genome can help gaining insight into 1,2-DCA dechlorination genes organization. The high degradation efficiency at a high 1,2-DCA concentration make the consortium exploitable for biaugmentation applications.