Unusual bacterial community assembly of a simplified consortium reductively dechlorinating 1,2-dichloroethane

Halogenated compounds are extensively used in industry and agriculture. Their recalcitrance to degradation pose them as primary issues for public health. 1,2-dichloroethane (DCA) is considered among the most important halo-organics due to its diffusion, being an intermediate for the production of PVC. Health issues associated with DCA, put the achievement of successful bioremediation approaches as well as the identification of the microbes able to degrade it and the metabolic pathways involved as primary goals, since the accomplishment of the successful remediation of a polluted site is dependent on the knowledge of the key microbes equipped with the relevant catabolic genes. The aims of this work were the evaluation of the DCA biodegradative potential of the resident microbiome of an aquifer polluted with high levels of DCA, as well as the enrichment of bacteria directly involved in the dehalorespiration process. We present the characterization of the bacterial community originated from the contaminated aquifer and its development in anaerobic microcosms after biostimulation with different e- donors. Moreover series of subsequent enrichments cultures were established.We have assessed the structural analysis of the bacterial communities involved in the degradation making use of several 16S rRNA-based molecular methods such as clone libraries, DGGE, ILLUMINA as well as flow-citometry. Following the biostimulation treatment the bacterial community underwent a notable change, with the enrichment of representatives of the order Clostridiales. On the other hand the enrichment cultures showed a gradually increasing dichlorinating performance, up to 50 ppm of DCA day-1 degraded. A gradual simplification of the community was observed resulting in the achievement of an enriched dehalogenating consortium, with two strains potentially involved in the contaminant depletion, a Geobacter sp. and a Pseudomonas sp. Neither of them was previously associated to DCA reductive dehalogeantion. Psedomonas sp. was isolated from the dehalogenating consortium and showed no chlororespiring capability when inoculated in aneaerobic as well as aerobic cultures with DCA, suggesting Geobacter sp. as the putative dehalogenating bacterium