A new study reveals how the interaction between Sargassum spp. And plastic marine debris and Vibrio bacteria creates the perfect “pathogen” storm that has implications for both marine life and public health. Vibrio bacteria are found in waters around the world and are the dominant cause of death for humans from the marine environment. For example, Vibrio vulnificus, sometimes referred to as a flesh-eating bacteria, can cause life-threatening foodborne illness from seafood consumption as well as illness and death from open wound infections.
Since 2011, Sargassum, free-living groups of brown macroalga, have expanded rapidly in the Sargasso Sea and other parts of the open ocean such as the Great Atlantic Belt Sargassum, including frequent and unprecedented seaweed build-up events on beaches. Plastic marine debris, first found in the surface waters of the Sargasso Sea, has become a global concern and is known to last decades longer than natural substrates in the marine environment.
Currently, little is known about the ecological relationship of Vibrio with Sargassum. Furthermore, genomic and metagenomic evidence has been missing on whether Vibrio that colonizes plastic marine debris and Sargassum can infect humans. With summer fast approaching and efforts underway to find innovative solutions to repurpose sargassum, could these substrates pose a triple threat to public health?
Florida Atlantic University researchers and collaborators sequenced the genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris, and seawater samples collected from the Caribbean Sea and Sargasso Sea in the North Atlantic Ocean. What they discovered is that Vibrio pathogens have a unique ability to “stick” to microplastics and that these microbes may adapt to the plastic.
“Plastics are a new element that has been introduced into marine environments and has only been around for about 50 years,” said Tracy Mencer, PhD, corresponding lead author and assistant professor of biology at FAU’s Harbor Branch Oceanographic Institution and Harriet L. Wilkes College Emeritus. “Our lab work showed that these Vibrio are very aggressive and can search for and latch on to plastic in a matter of minutes. We also found that there are binding factors that microbes use to stick to plastic, which is the same mechanism that pathogens use.”
The study, published in the journal Water Research, shows that open ocean vibrios represent a hitherto undescribed group of microbes, some representing potential new species, that possess a mixture of disease-causing genes and low nutrients, reflecting their surface habitat, substrates and colonizing hosts. Using the assembled metagenome (MAG) genome, this study represents the first Vibrio spp. The genome was assembled from plastic debris.
The study highlighted the genes of vertebrate pathogens closely related to bacterial strains other than cholera and cholera. Phenotype testing of the cultivars confirmed rapid biofilm formation, and lipid lytic and phosphorylation activities, consistent with pathogenic potential.
The researchers also discovered that the zonula’s toxin-containing or “zot” genes, first described in Vibrio cholerae, a secreted toxin that increases intestinal permeability, were some of the most sequestered and selected for in Vibrio cholerae they found. It seems that these Vibrio enter through the gut, get stuck in the intestines and infect in this way.
“Another interesting thing that we discovered is a group of genes called ‘zot’ genes, which cause leaky gut syndrome,” Mencer said. “For example, if a fish eats a piece of plastic and becomes infected with this Vibrio, which then leads to leaky gut and diarrhea, it will release waste nutrients like nitrogen and phosphate that can stimulate the growth of sargassum and other surrounding organisms.”
Results show some Vibrio spp. In this environment an “omnivorous” lifestyle targets both plant and animal hosts along with the ability to survive in oligotrophic conditions. With the increase of human-sargassum-plastic interactions of marine debris, the microbial flora associated with these substrates could harbor potent opportunistic pathogens. Importantly, some of the cultivation-based data show that Sargassum on the beach appears to harbor large amounts of Vibrio bacteria.
“I don’t think, at this point, anyone has really thought about these microbes and their ability to cause infection,” Mencer said. “We really want to make the public aware of these associated risks. In particular, care needs to be taken with regard to the harvesting and processing of Sargassum biomass until the risks are explored more thoroughly.”
Study co-authors represent the Royal Netherlands Institute for Marine Research, the Japan Agency for Marine Geoscience and Technology, Ludwig Maximilian University Munich, Germany, Emory University, the University of Amsterdam, and the Marine Biological Laboratory.
This research was supported by the National Science Foundation (NSF) (OCE grant-1155671 awarded to Mincer), FAU World Class College and Scholar Program (awarded to Mincer), NSF (OCE grant-1155571 awarded to Linda A. Amaral-Zettler, Ph.D., matching author, NIOZ), NSF (OCE-1155379 grant awarded to Erik R. Zettler, Ph.D., co-author, NIOZ), NSF TUES grant (DUE-1043468 awarded to Linda Zettler and Erik Zettler).