Functional genotyping of Sulfurospirillum spp. in mixed cultures allowed the identification of a new tetrachloroethene reductive dehalogenase

Chlorinated compounds are widespread soil and groundwater pollutants. Because of industrial activities, large amounts of chlorinated ethenes were discharged into the environment over the last decades. The underlying biodegradation process, organohalide respiration (OHR), is a bacterial anaerobic respiration in which the chlorinated compounds, such as chloroethenes, are used as terminal electron acceptors. The key catalytic enzyme in OHR is the reductive dehalogenase (RdhA). SL2-PCEb, an enrichment culture dominated by Sulfurospirillum spp., was shown to stepwise dechlorinate PCE to trichloroethene (TCE) and cis-dichloroethene (cis-DCE), suggesting the successive involvement of multiple populations. However neither T-RFLP on 16S rRNA genes nor the analysis of the 16S-23S intergenic spacer (ITS) allowed identifying distinct Sulfurospirillum strains. Recently, two subcultures were derived from SL2-PCEb showing distinct dechlorination potential: SL2-PCEc which dechlorinates PCE to TCE only, and SL2-TCE which was selected on TCE but kept the potential to dechlorinate both PCE and TCE. As genotyping based on rRNA genes was not possible here, cloning/sequencing of rdhA genes and a T-RFLP method dedicated to distinguish the functional genes were successfully applied allowing the identification of a new RdhA from Sulfurospirillum, PceATCE, involved in the dechlorination of PCE to TCE exclusively. This new subculture, SL2-PCEc, is now the focus of several new investigation lines which will be also presented.