Syntrophic Partners Enhance Growth and Respiratory Dehalogenation of Hexachlorobenzene by Dehalococcoides mccartyi Strain CBDB1.

Anh T. T. Chau,Michael J. Manefield,Lorenz Adrian,Matthew Lee

doi:10.3389/fmicb.2018.01927

Anh T. T. Chau, Michael J. Manefield + Show 2 more

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https://doi.org/10.3389/fmicb.2018.01927

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Abstract

This study investigated syntrophic interactions between chlorinated benzene respiring Dehalococcoides mccartyi strain CBDB1 and fermenting partners (Desulfovibrio vulgaris, Syntrophobacter fumaroxidans, and Geobacter lovleyi) during hexachlorobenzene respiration. Dechlorination rates in syntrophic co-cultures were enhanced 2-3 fold compared to H2 fed CBDB1 pure cultures (0.23 ± 0.04 μmol Cl− day−1). Syntrophic partners were also able to supply cobalamins to CBDB1, albeit with 3–10 fold lower resultant dechlorination activity compared to cultures receiving exogenous cyanocobalamin. Strain CBDB1 pure cultures accumulated ~1 μmol of carbon monoxide per 87.5 μmol Cl− released during hexachlorobenzene respiration resulting in decreases in dechlorination activity. The syntrophic partners investigated were shown to consume carbon monoxide generated by CBDB1, thus relieving carbon monoxide autotoxicity. Accumulation of lesser chlorinated chlorobenzene congeners (1,3- and 1,4-dichlorobenzene and 1,3,5-trichlorobenzene) also inhibited dechlorination activity and their removal from the headspace through adsorption to granular activated carbon was shown to restore activity. Proteomic analysis revealed co-culturing strain CBDB1 with Geobacter lovleyi upregulated CBDB1 genes associated with reductive dehalogenases, hydrogenases, formate dehydrogenase, and ribosomal proteins. These data provide insight into CBDB1 ecology and inform strategies for application of CBDB1 in ex situ hexachlorobenzene destruction technologies.

Highlights

Chlorinated benzenes including hexachlorobenzene (HCB) are toxic and persistent compounds that have been studied extensively in the context of microbiological degradation (Field and Sierra-Alvarez, 2008)
Dechlorination rates were comparable with the different partners with the highest observed in the D. vulgaris and CBDB1 (DSV/CBDB1) co-culture (0.59 ± 0.05 μmol Cl− day−1) with the rates in the other co-cultures at 0.39 ± 0.15 and 0.45 ± 0.09 μmol Cl− day−1 in the S. fumaroxidans and CBDB1 (SFO/CBDB1) and G. lovleyi and CBDB1 (GBL/CBDB1) cocultures, respectively (Table 1)
We provide the first description of syntrophic growth of D. mccartyi strain CBDB1 and partners (Desulfovibrio vulgaris, Syntrophobacter fumaroxidans and Geobacter lovleyi) for exogenous provision of H2, acetate and cobalamin for the reductive dechlorination of HCB

Summary

Introduction

Chlorinated benzenes including hexachlorobenzene (HCB) are toxic and persistent compounds that have been studied extensively in the context of microbiological degradation (Field and Sierra-Alvarez, 2008). Whilst lesser chlorinated benzenes are susceptible to aerobic biodegradation in conventional activated sludge treatment processes (van Agteren et al, 1998) microbes can Syntrophy in Hexachlorobenzene Dehalogenation only degrade hexachlorobenzene, pentachlorobenzene, 1,2,3,4tetrachlorobenzene, and 1,3,5-trichlorobenzene through anaerobic or reductive reactions (Adrian and Görisch, 2002). Such reductive reactions have been linked to bacterial growth (Adrian and Görisch, 2002) and have potential as a biotechnology for commercial chlorinated benzene disposal. D. mccartyi strain CBDB1 grows in mineral medium with H2 as the electron donor, acetate as an organic carbon source, and chlorobenzenes as electron acceptors, in conjunction with cyanocobalamin as an essential cofactor (Adrian et al, 2000)

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