Reductive debromination by sponge-associated anaerobic bacteria coupled to carbon isotope fractionation

Marine sponges contain diverse brominated compounds as secondary metabolites and the sponge habitat appears to enrich for a population of anaerobic dehalogenating bacteria. Hence, there is interest in understanding how these natural and anthropogenic compounds are degraded in the marine environment. Compound specific isotope analysis (CSIA) is a useful tool to monitor and to quantify the degradation and fate of aquatic pollutants. The objective of this study was to evaluate whether reductive dehalogenation of brominated phenols by sponge-associated bacteria, including Desulfoluna spongiiphila, can be monitored by CSIA. Debromination of 2,6-dibromophenol to phenol by sponge-associated cultures resulted in measurable stable carbon isotope fractionation. All sponge-associated cultures showed similar isotopic enrichment factors (ε). The ε values for two independent sponge-derived dehalogenating cultures were -3.1 ± 1.5‰, and -3.0 ± 0.3‰, and that of sponge associated sediment cultures -2.0 ± 0.3‰. Thus, we demonstrate that reductive debromination of 2,6-dibromophenol resulted in measurable carbon isotope fractionation and that CSIA can be used to assess reductive debromination and to monitor and estimate in vivo dehalogenation in a sponge animal.