Halogenated Natural Products of environmental relevance in the marine environment

Investigating the sources, transformations and fates of brominated compounds in the marine environment

Our understanding of halogenated organic compounds in the environment has changed significantly over the past three decades. Notably, an increasing number of organobromine species previously assumed to be remnants or metabolites of anthropogenic pollutants are now being identified as natural products. The pollutants in question, polybrominated diphenyl ethers (PBDE) have been widely used since the 1970s as flame retardants in numerous industrial and residential applications. They have since joined the ranks of polychlorinated biphenyls and other persistent organic pollutants due to their widespread use, environmental ubiquity, bioaccumulation patterns and resulting toxicity. There has been increasing concern over PBDDs (polybrominated dibenzo-p-dioxins) due to their structural similarity to the highly toxic chlorinated analogues. Studies have implicated biotic and abiotic transformations of PBDE flame retardants in the formation of PBDDs (e.g. Buser, 1986). However, related species, hydroxylated polybrominated diphenyl ethers (OH-PBDEs; Haglund et al., 2007) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs; Teuten et al., 2005), have also been isolated from marine biota in many aquatic systems, and several recent studies have implicated these compounds as potential natural sources of PBDDs in the marine environment.

We are currently working towards the isolation and quantification of MeO-PBDEs, OH-PBDEs and PBDDs from mussel tissues in coastal environments, with the ultimate goal of using natural abundance radiocarbon analysis to determine their potential contribution to local environments.

We are also working to determine the biological source and distribution of the genetic potential for production of MeO-PBDEs. Though MeO-PBDEs have been primarily found accumulating in tissues of higher organisms it has been proposed that bacteria (including cyanobacteria) are the potential natural source (Elyakov et al., 1991). However, the ubiquity of natural MeO-PBDE sources remains undemonstrated. Based on ongoing environmental metagenomes searches, I have determined that biosynthetic clusters for biohalogenation via flavin-dependent halogenases are prevalent in marine surface waters. This initial data suggests that microorganisms with the ability to synthesize MeO-PBDEs are pervasive in marine surface and deep waters. I am currently investigating the diversity of these enzymes and trying to determine their phylogenetic affiliation.