A research team at the University of California San Diego (UCSD) discovered that a common marine sponge hosts bacteria that produce toxic compounds that are nearly identical to man-made flame retardants.
The new findings, which are featured on the May cover of the journal Nature Chemical Biology, bring the research team one step closer to unraveling the mystery of this powerful group of chemical compounds, known as polybrominated diphenyl ethers (PBDEs), in the marine environment.
Man-made PBDEs are combined into foam, textiles, and electronics to reduce flammability by raising the temperature at which the products will burn. They also mimic the activity of the human body's own hormones, so PBDEs are known as endocrine disruptors.
“We care about naturally produced PBDEs because they end up in the food chain,” said Frederick Tyson, Ph.D., director of the NIEHS Oceans and Human Health (OHH) program, which helped to fund the research. “Preliminary data suggest that some naturally occurring PDBEs may be more toxic than the man-made compounds, so we need to understand them.”
Discovery builds on previous findings
Vinayak Agarwal, Ph.D., a postdoctoral researcher at the UCSD Scripps Institute of Oceanography, picked up a cold case that Scripps chemist John Faulkner, Ph.D., began nearly 50 years ago. Agarwal continued Faulkner’s investigation into the source of naturally produced PBDEs in the world’s oceans.
“For the first time, we were able to conclusively show that genes and enzymes produced in bacteria from sponges are responsible for the production of these compounds,” said Agarwal, co-first author of the paper, along with Scripps graduate student Jessica Blanton.
In 2014, Agarwal and colleagues discovered a different source of naturally produced PBDEs — free-living marine bacteria. Both studies were conducted through the Scripps Center for Oceans and Human Health and jointly funded by NIEHS and the National Science Foundation (NSF).
Genome mining helps find the source
Marine sponges host complex microbiomes that include bacteria, viruses, and fungi. The research team collected 18 sponge samples from the reef near Guam, and they isolated components of the microbiome. To identify the specific genes and enzymes that code for the production of PBDEs, the scientists used two modern day techniques. The first, genome mining, was pioneered by Scripps marine chemist Brad Moore, Ph.D., who was a senior author of the study.
The second technique is an approach for sequencing DNA from environmental samples such as soil, sediment, and water. The technique, called metagenomics sequencing, was pioneered by Scripps biologist Eric Allen, Ph.D.
“For many years scientists were finding clues that suggested nature was making these compounds,” said Moore. “Now that we understand how they are produced, we are exploring why they exist and the human health concerns associated with them.”
Links between oceans and human health
“This study has the potential to help us understand the production, fate, and health consequences of natural and pollutant compounds in the marine environment,” said Henrietta Edmonds, Ph.D., of the NSF Division of Ocean Sciences.
Tyson agreed, saying the research supports the OHH focus on either man-made pollutants or natural chemical toxins that may affect human health. “Toxic chemicals are toxic chemicals, wherever they come from,” he said.
One of the Scripps projects analyzes samples of breastmilk from women in the San Diego area to determine levels of naturally produced PBDEs in consumers of local seafood. “We’re still learning how substantial the body burden is,” said Tyson. “All of this is about better understanding these compounds, how they’re being made, and potential impacts to human health.”
Citation: Agarwal V, Blanton JM, Podell S, Taton A, Schorn MA, Busch J, Lin Z, Schmidt EW, Jensen PR, Paul VJ, Biggs JS, Golden JW, Allen EE, Moore BS. 2017. Metagenomic discovery of polybrominated diphenyl ether biosynthesis by marine sponges. Nat Chem Biol 13(5):537−543.
(This story is based on a press release from the Scripps Institute of Oceanography at UCSD.)