New putative 1,2-dichloroethane dehalorespiring bacteria

Halogenated organic compounds are extensively used in a broad range of productive sectors. These chemicals pose as primary public health issues because of their diffusion in all aquatic environments caused by commercial application, incorrect waste disposal and accidental leaks. 1,2-Dichloroethane (1,2-DCA) is one of the most important halogenated compounds quantitatively, being used as an intermediate for polyvinyl chloride production. Several halorespiring bacteria have been identified and cultured, able to use this halogenated molecule as terminal electron acceptors for an anaerobic metabolic process called dehalorespiration. However untill now, only a few bacterial species with the ability of converting 1,2-DCA into ethene have been identified, mainly belonging to the order Clostridiales. The aim of this work was to identify and enrich bacteria directly involved in the dehalorespiration process from groundwaters historically polluted by high levels of 1,2-DCA. A series of subsequent culture dilutions were established in microcosms, where the microbial community of the aquifer was grown in mineral media supplemented with 1,2-DCA as electron acceptor and lactate or acetate+formate as electron donors. 1,2-DCA degradation was monitored by head-space gas-chromatography. All microcosms showed dehalogenating activity with degradation rates up to 40 ppm 1,2-DCA day-1. Bacterial phylogenetic diversity was monitored by different 16S rRNA gene-based molecular approaches such as PCR-Denaturing Gradient Gel Electrophoresis, barcoded pyrosequencing and fluorescent in situ hybridization. The results demonstrated a gradual simplification of the bacterial community in microcosms supplied with acetate+ formate as electron donors resulting in the enrichment of few bacterial species, potentially involved in the contaminant depletion, interestingly not belonging to Clostridiales, but to γ- and δ-Proteobacteria.