Interrogating novel biosynthetic sources for the production of polybrominated diphenyl ethers

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Project Summary/Abstract The presence of polybrominated diphenyl ethers (PBDEs) in the ocean has been a human health hazard since their implementation as flame retardants in the 1970s, causing a myriad of toxic effects including thyroid hormone imbalances, neurotoxicity, and developmental disorders. Since 2004, the entrance of anthropogenic PBDEs into the environment has been limited by government restrictions on their production. However, this environmental health crisis remains as PBDEs continue to be detected around the globe, impacting commonly consumed seafood, marine mammals, and humans. In 2005, it was discovered that not all PBDEs are of anthropogenic origin; commonly detected hydroxylated and methoxylated PBDEs (OH-BDEs and MeO-BDEs, respectively) were found to be natural products. Furthermore, the toxicity of OH-BDEs and MeO-BDEs were found to surpass that of anthropogenic PBDEs. Studies have demonstrated the persistence of PBDEs and their hydroxylated and methoxylated congeners in the environment and their ability to be passed through the food web; however, the handful of known OH/MeO-BDE bacterial and algal producers do not account for the global representation of the molecules in the oceans. Here, I propose to explore the possibility of novel OH/MeO-BDE producers by examining probable common dietary sources by searching for clues in sea water, ocean sediments, and marine animal-associated microbiota. This proposal aims to mine metagenomic and metatranscriptomic data from environmental samples to assess the distribution of OH/MeO-BDE producers in the environment and the chemistry employed in the biosynthetic machinery. The sequences of known OH/MeO-BDE biosynthesis enzymes from marine bacteria will be used initially as probes, followed by the use of biosynthetic logic to identify new enzymes of interest. In Aim 1, I will use this approach toward OH/MeO-BDE-producing red algae to establish, for the first time, the molecular basis for PBDE biosynthesis in an eukaryotic system. Differential expression analysis under low and high producing conditions will be employed to facilitate the identification of putative biosynthetic genes. In Aim 2, known bacterial genes and newly identified eukaryotic genes will be used as probes to assess metagenomic data from sea water, sediment, and marine animal associated microbes for the presence of PBDE biosynthesis genes. Finally, the enzymology of PBDE biosynthetic enzymes will be explored in Aim 3 to provide a detailed understanding of the underlying mechanisms of PBDE biosynthesis, specifically in the unique flavin dependent halogenases responsible for aromatic decarboxylative bromination. I anticipate that this research will provide an invaluable understanding of PBDE biosynthesis and its global distribution. Furthermore, this research will likely facilitate studies to manage PBDE production in the environment and provide new insights into understudied classes of enzymes.