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bioRxiv · 10.1101/2020.12.18.423565

Longitudinal study of vinyl chloride degrading Dehalococcoides mccartyi-containing cultures to promote horizontal gene transfer

Morson, N.·Molenda, O.·Picott, K. J.·Richardson, R. E.·Edwards, E. A.
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Abstract

Few strains of Dehalococcoides mccartyi harbour and express the vinyl chloride reductase (VcrA) that catalyzes the dechlorination of vinyl chloride (VC), a carcinogenic soil and groundwater contaminant. The vcrA operon is found on a Genomic Island (GI) and therefore believed to participate in horizontal gene transfer. To try to induce horizontal gene transfer of the vcrA-GI, we blended two enrichment cultures in medium without ammonium while providing VC. We hypothesized that these conditions would select for a mutant strain of D. mccartyi that could both fix nitrogen and respire VC. However, after more than 4 years of incubation, we found no evidence for horizontal gene transfer of the vcrA-GI. Rather, we observed VC-dechlorinating activity attributed to the trichloroethene reductase TceA. Sequencing and protein modelling revealed a mutation in the predicted active site of TceA which may have influenced substrate specificity. We also identified two nitrogen-fixing D. mccartyi strains in the KB-1 culture. The presence of multiple strains of D. mccartyi with distinct phenotypes is a feature of natural environments and certain enrichment cultures (such as KB-1) and may enhance bioaugmentation success. The fact that multiple distinct strains persist in the culture for decades and that we could not induce horizontal gene transfer of the vcrA-GI suggests that it is not as mobile as predicted, or that mobility is restricted in ways yet to be discovered to specific sub-clades of Dehalococcoides. TOC Art O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/423565v2_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@80423forg.highwire.dtl.DTLVardef@7d6484org.highwire.dtl.DTLVardef@5223b2org.highwire.dtl.DTLVardef@a58aab_HPS_FORMAT_FIGEXP M_FIG C_FIG

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Morson, N., Molenda, O., Picott, K. J., Richardson, R. E., Edwards, E. A.. 2020-12-20. Longitudinal study of vinyl chloride degrading Dehalococcoides mccartyi-containing cultures to promote horizontal gene transfer. https://doi.org/10.1101/2020.12.18.423565

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