'Perfect Pathogen Storm': Sargassum Seaweed May Be Harboring Flesh-Eating Bacteria Too

Massive sargassum blooms aren't just a nuisance because of the putrid smell they emit when they rot. They may also be harboring pathogens like flesh-eating bacteria, researchers have found.

These, together with plastic marine debris, could be creating a "perfect pathogen storm."

Vibrio bacteria inhabit various environments like coastal marine, freshwater and open ocean habitats, the researchers noted in their study, which was published in the journal Water Research. These include pathogens like Vibrio cholerae, which is behind cholera pandemics, and the infamous Vibrio vulnificus, more commonly known to many as flesh-eating bacteria.

For their study, the researchers looked at Vibrio cultivars from plastic marine debris (PMD), eel larvae, seawater and Sargassum.

Sargassum is a large brown seaweed that floats in enormous masses. This can provide food for various creatures and even energy once it has sunk to the seafloor. However, it may also have negative impacts, like stopping the light from reaching the corals below, blocking the shore and producing a foul smell like rotten eggs once it rots.

So far, not much is known about the relationship between Vibrios and Sargassum, the Florida Atlantic University (FAU) noted. But in their work, the researchers found a rather interesting, albeit concerning, way that Vibro bacteria, Sargassum and marine plastic, which has turned into a "worldwide concern," interact.

They found that beached Sargassum appears to be harboring "high amounts" of Vibrio bacteria and that these pathogens have the "unique ability to 'stick'" to the microplastics. This suggests that the pathogens are adapting to plastic, according to the FAU. Furthermore, they found that Vibrio bacteria are quite omnivorous, targeting both plant and animal hosts.

"Our lab work showed that these Vibrioare extremely aggressive and can seek out and stick to plastic within minutes," study corresponding lead author Tracey Mincer of the FAU said, as per the university release. "We also found that there are attachment factors that microbes use to stick to plastics, and it is the same kind of mechanism that pathogens use."

Simply put, Vibrio pathogens appear to be quite good at colonizing plastic debris in marine environments. The combination of these factors could be problematic.

"With the increase of Sargassum and PMD in the Sargasso Sea and their growing co-occurrence in other parts of the open ocean such as the Great Atlantic Sargassum Belt in the North Equatorial Recirculation Region, open ocean Vibrio spp. colonizing these substrates are expanding as well," the researchers wrote.

Earlier this year, for instance, a massive Sargassum bloom made its way to Florida. It was so big that it was already reportedly visible from space, and it ended up covering some of Florida's beaches. Apart from the foul smell it emits, rotting Sargassum may also have impacts on air and water quality in surrounding areas.

Now having a better idea of how Sargassum interplays with plastic and Vibrio further highlights a potential risk associated with it that people have yet to consider.

However, the researchers' findings don't stop there.

"Another interesting thing we discovered is a set of genes called 'zot' genes, which causes leaky gut syndrome," Mincer explained. "For instance, if a fish eats a piece of plastic and gets infected by this Vibrio, which then results in a leaky gut and diarrhea, it's going to release waste nutrients such nitrogen and phosphate that could stimulate Sargassum growth and other surrounding organisms."

Sargassum, Vibrio and marine plastic could then be creating the "perfect pathogen storm" that may have implications for marine and public health, the FAU noted.

All in all, it appears that these three factors together could be perpetuating a rather concerning cycle, and it seems that scientists are still on their way to truly understanding the scope of the relationship between these factors.

"With increased human-Sargassum-PMD interactions, associated microbial flora of these substrates could harbor potent opportunistic pathogens," the researchers wrote, warning in particular about the potential risks that may come about from harvesting and processing of Sargassum biomass.

Infections with the infamous Vibrio vulficicus, for instance, are considered to be rare. But in 2022 Florida saw an unusual increase in cases with reported 74 infections and 17 deaths compared to the 36 logged in 2020 and the 34 reported in 2021. This increase was reportedly due to some of the impacts of Hurricane Ian.

"I don't think at this point, anyone has really considered these microbes and their capability to cause infections," Mincer said. "We really want to make the public aware of these associated risks."