Novel aerobic 1,2-DCA biodegrading consortia immobilized on biopolymeric scaffolds for enhanced bioremediation of contaminated groundwater

Abstract

Sustainable nature-based solutions are urgently needed to address environmental health challenges in line with the Sustainable Development Goals. 1,2-dichloroethane (1,2-DCA) is a recalcitrant, toxic and probably carcinogenic groundwater contaminant whose biodegradation is generally attributed to specialized anaerobic bacteria1. However aerobic hydrolytic dechlorination, mediated by the key enzyme DhlA, is also a potentially valid approach in bioremediation1. Biodegrading biofilms applied to bioremediation are a cost-effective strategy to enhance the clean-up of water contaminated by organic pollutants2,3. The aim of this work was to develop a bioremediation device based on novel aerobic 1,2-DCA-degrading consortia immobilized on biodegradable scaffolds to be exploited in bioaugmentation strategies. The 3D biodegradable biopolymeric polylactic acid (PLA) scaffold, produced by electrospinning, was preliminarily assessed as the most suitable to host a microbial biofilm and absorb 1,2-DCA. Two novel 1,2-DCA degrading consortia (named A and B) were isolated from 1,2-DCA contaminated groundwater through enrichment cultures on mineral medium amended with 1,2-DCA as sole carbon source. The composition of the consortia was analyzed by Ion Torrent 16S rRNA gene sequencing. The dhlA gene encoding for the hydrolytic dechlorination key enzyme was searched by PCR assay and its location was assessed by Whole Genome Sequencing. The 1,2-DCA degrading devices were obtained by immobilizing the consortia on the PLA scaffolds and the maintenance of their catabolic activity was tested after transferring them into a fresh 1,2-DCA amended medium. The scaffold colonization by the consortia was assessed by Scanning Electron Microscopy. 1,2-DCA removal by the devices before and after the transfer was monitored by Gas Chromatography-Mass Spectrometry (GC-MS). The composition of the consortia was similar and included the known aerobic 1,2-DCA-degrading genus Ancylobacter, as well as other members with yet unclear role. Ancylobacter carried on its chromosome a dhlA gene identical to that of other known aerobic 1,2-DCA-degraders. The consortium-scaffold systems (Fig. 1a, b) degraded up to 1000 ppm 1,2-DCA within seven days, and maintained the biodegrading ability after the transfer (Fig. 1c). In conclusion, these devices based on the novel highly efficient 1,2-DCA-degrading consortia immobilized on biopolymeric supports are suitable to be applied in enhanced bioremediation treatments, including permeable reactive barriers and bioreactors.