A beachgoer walks through sargassum seaweed that washed ashore on 18 May 2023, in Key West, Florida. A huge mass of sargassum seaweed formed in the Atlantic Ocean is headed for the Florida coastlines and shores in the Gulf of Mexico. Photo: Joe Raedle / Getty Images
A beachgoer walks through sargassum seaweed that washed ashore on 18 May 2023, in Key West, Florida. A huge mass of sargassum seaweed formed in the Atlantic Ocean is headed for the Florida coastlines and shores in the Gulf of Mexico. Photo: Joe Raedle / Getty Images

By Jess Thomson
30 May 2023

(Newsweek) – The massive blob of seaweed creeping across the Atlantic Ocean toward Florida may contain deadly flesh-eating bacteria.

The 5,000-mile wide clump of seaweed is made up of sargassum seaweed, which has bloomed massively to form the “Great Atlantic Sargassum Belt.”

A study from Florida Atlantic University published in the journal Water Research found that the sargassum and its accompanying floating plastic can become inundated with species of Vibrio bacteria, creating a “perfect pathogen storm.”

The researchers found that beached sargassum seaweed is home to high levels of the bacteria and that the bacteria can readily cling to the surface of marine plastic debris, which accumulates in large volumes within the mass of seaweed.

Illustration showing how genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris (PMD), the pelagic brown macroalga Sargassum, and seawater samples were collected from the Caribbean and Sargasso Seas of the North Atlantic Ocean. Graphic: Mincer, et al., 2023 / Water Research
Illustration showing how genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris (PMD), the pelagic brown macroalga Sargassum, and seawater samples were collected from the Caribbean and Sargasso Seas of the North Atlantic Ocean. Graphic: Mincer, et al., 2023 / Water Research

Vibrio bacteria, notably the Vibrio vulnificus species, can lead to brutal infections and even necrotizing fasciitis, leading to the bacteria being nicknamed “flesh-eating.” Vibrio can infect via eating contaminated seafood, or through an open wound on someone’s flesh, usually from seawater, according to the Centers for Disease Control and Prevention. Infected wounds may become necrotic, with the flesh itself dying and rotting.

Around 1 in 5 people with the infection die, the CDC states, usually rapidly after becoming infected. Thankfully, necrotizing fasciitis is rare: only about 0.4 people per 100,000 are infected each year in the United States.

“I don’t think at this point, anyone has really considered these microbes and their capability to cause infections,” Tracy Mincer, lead author of the Water Research paper and assistant professor of biology at FAU’s Harbor Branch Oceanographic Institute and Harriet L. Wilkes Honors College, said in a statement.

“We really want to make the public aware of these associated risks. In particular, caution should be exercised regarding the harvest and processing of Sargassum biomass until the risks are explored more thoroughly.”

The seaweed blob has only been growing: researchers at the University of South Florida’s Optical Oceanography Lab found that in March and April, the seaweed clump was estimated to contain about 13 million tons of sargassum, a record amount for that time of year. [more]

Seaweed Full of Flesh-Eating Bacteria Hitting Florida

Vibrio pangenome analysis of isolates analyzed in this study. The circular phylogram was created using Anvi'o 7.0 analyses of 16 environmental Vibrio isolates. The colors indicate the respective marine substrate from which each cultivar was isolated: eel leptocephalus (orange), plastic marine debris (red), Sargassum (green), seawater (blue), and type strains (black). All environmental cultivars were tested for biofilm formation, bioluminescence, hemolysis, and phospholipase activity (see Supplemental Information). Results are color-coded in the legend. Average nucleotide identity (ANI) ranges between 100% (dark red) and 70% (pink) are also indicated, with the cladogram at the top right indicating ANI clustering. SCGs indicated by the outer circle denotes single copy genes. Strain names indicated at top continue through the circular dendrogram to the ANI and clade diagram. Graphic: Mincer, et al., 2023 / Water Research
Vibrio pangenome analysis of isolates analyzed in this study. The circular phylogram was created using Anvi’o 7.0 analyses of 16 environmental Vibrio isolates. The colors indicate the respective marine substrate from which each cultivar was isolated: eel leptocephalus (orange), plastic marine debris (red), Sargassum (green), seawater (blue), and type strains (black). All environmental cultivars were tested for biofilm formation, bioluminescence, hemolysis, and phospholipase activity (see Supplemental Information). Results are color-coded in the legend. Average nucleotide identity (ANI) ranges between 100% (dark red) and 70% (pink) are also indicated, with the cladogram at the top right indicating ANI clustering. SCGs indicated by the outer circle denotes single copy genes. Strain names indicated at top continue through the circular dendrogram to the ANI and clade diagram. Graphic: Mincer, et al., 2023 / Water Research

Sargasso Sea Vibrio bacteria: Underexplored potential pathovars in a perturbed habitat

ABSTRACT: We fully sequenced the genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris (PMD), the pelagic brown macroalga Sargassum, and seawater samples collected from the Caribbean and Sargasso Seas of the North Atlantic Ocean. Annotation and mapping of these 16 bacterial genome sequences to a PMD-derived Vibrio metagenome-assembled genome created for this study showcased vertebrate pathogen genes closely-related to cholera and non-cholera pathovars. Phenotype testing of cultivars confirmed rapid biofilm formation, hemolytic, and lipophospholytic activities, consistent with pathogenic potential. Our study illustrates that open ocean vibrios represent a heretofore undescribed group of microbes, some representing potential new species, possessing an amalgam of pathogenic and low nutrient acquisition genes, reflecting their pelagic habitat and the substrates and hosts they colonize.

Sargasso Sea Vibrio bacteria: Underexplored potential pathovars in a perturbed habitat