Diversity of 1,1,1-trichloroethane degrading Dehalobacter spp. in contaminated groundwater

Abstract:

[Objective] In order to study the diversity of Dehalobacter spp. from six 1,1,1-trichloroethane (TCA) contaminated groundwater samples. [Methods] The concentration of 1,1,1-TCA, 1,1-dichloroethane (DCA) and chloroethane (CA) of each sample was determined using gas chromatography. Real-time qPCR was performed on each sample to estimate the ratio of Dehalobacter spp. (Dhb) to the total bacteria. PCR products amplified by combining 16S rRNA gene universal primer and Dehalobacter group-specific primer were used to construct six Dhb group-specific clone libraries, respectively. Phylogenetic tree was constructed based on the sequences from the clone libraries and their nearest neighbors from GenBank. [Results] The existence of 1,1-DCA and (or) CA in the 6 samples may associate with 1,1,1-TCA biodegradation. Real-time qPCR results demonstrated that the ratio of Dhb to the total bacteria varied in each sample. In total 41 sequences were obtained from these 6 clone libraries and BLAST showed all their nearest sequences were affiliated to Dhb. These sequences were clustered into 7 operational taxonomic units (OTUs) at a threshold of 99% similarity. OTU1 (24 sequences) has a similarity of 98% with the 1,1,1-TCA reductively dechlorinating strain Dehalobacter sp. str. TCA1. Three other OTUs only has 95%?96% similarity with their nearest 16S rRNA gene sequences in GenBank. [Conclusion] This study demonstrated the existence of Dhb in all 6 samples with a relatively high diversity and these Dhb bacteria might be responsible for the biodegradation of 1,1,1-TCA in the groundwater of sampling sites.

Key words:1,1,1-Trichloroethane, Dehalobacter, 16S rRNA gene clone library, Real-time qPCR, Biodegradation, Diversity