The interplay between Sargassum spp., plastic marine debris, and Vibrio bacteria has been uncovered in a new study, revealing a concerning « pathogen » storm that affects marine life and public health. Vibrio bacteria, known to be the leading cause of death in humans from the marine environment, including flesh-eating bacteria, pose a significant threat. Since 2011, Sargassum, a type of brown macroalgae, has been rapidly expanding in the Sargasso Sea and other open ocean areas, leading to unprecedented accumulation events on beaches. Plastic marine debris, which persists longer than natural substrates, has become a global concern.
Little is known about the ecological relationship between vibrios and Sargassum, and there has been a lack of genomic evidence regarding the potential infection of humans by vibrios colonizing plastic marine debris and Sargassum. As efforts to repurpose Sargassum continue, concerns arise about the triple threat to public health posed by these substrates.
Researchers from Florida Atlantic University and collaborators conducted a study in which they sequenced the genomes of 16 Vibrio strains isolated from various sources, including eel larvae, plastic marine debris, Sargassum, and seawater samples from the Caribbean and Sargasso seas. They discovered that Vibrio pathogens have the ability to adhere to microplastics, suggesting an adaptation to plastic. The researchers also found that the attachment mechanism used by microbes to stick to plastics is similar to that used by pathogens.
The study, published in Water Research, revealed that open ocean vibrios represent a previously undescribed group of microbes, some of which may be new species. These microbes possess a combination of pathogenic and low nutrient acquisition genes, reflecting their habitat and the substrates and hosts they colonize. The study also assembled the first Vibrio spp. genome from plastic debris using metagenome-assembled genome (MAG) techniques.
The researchers identified vertebrate pathogen genes related to cholera and non-cholera bacterial strains. Phenotype testing confirmed the potential pathogenicity of these strains through rapid biofilm formation, hemolytic and lipophospholytic activities. The study also revealed the presence of zonula occludens toxin or « zot » genes, which increase intestinal permeability and are associated with Vibrio cholerae. These genes indicate that these vibrios may enter the gut, causing infections and leading to leaky gut syndrome and diarrhea. The waste nutrients released as a result of the infection could stimulate the growth of Sargassum and other organisms in the surrounding environment.
The findings suggest that some Vibrio spp. in this environment have an « omnivorous » lifestyle, targeting both plant and animal hosts, while being able to survive in low-nutrient conditions. With increasing interactions between humans, Sargassum, and plastic marine debris, the microbial flora associated with these substrates could harbor potent opportunistic pathogens. Notably, cultivation-based data indicate that beached Sargassum may contain high amounts of Vibrio bacteria.
The study’s lead author, Tracy Mincer, emphasizes the need to raise awareness about the risks associated with these microbes and their potential to cause infections. The public should exercise caution regarding the harvest and processing of Sargassum biomass until further exploration of the risks has been conducted.
Read the study: https://www.sciencedirect.com/science/article/pii/S0043135423004694?via%3Dihub