Plastic microfibers in the Mediterranean Sea are keeping bacteria afloat

Plastic microfibers in the Mediterranean Sea are keeping bacteria afloat

Microbial life is naturally abundant in water bodies, and the Mediterranean Sea is no exception. The Mediterranean’s microscopic marine life has a new way to get around. They are riding on a growing number of plastic vessels, using microfibers as their ride.

In a recent study published on November 30 in the journal PLOS One, a team of biologists from Sorbonne Universite in France have discovered 195 species of bacteria living on microfibers floating in the Mediterranean Sea. According to their analysis, a single microfiber could be home to more than 2,600 bacterial cells. Although not all marine microbes found on the plastic particles are dangerous, the researchers were especially concerned about the potential danger to wildlife and humans from certain bacterial species.

“Plastics were a relatively new substrate within the ocean,” says Ana Luzia deFigueiredo Lacerda study author, and a marine plastic pollution researcher from Sorbonne Universite.

A 2020 United Nations Environment Program report estimates that 730 tons of plastic waste end up in the Mediterranean Sea every day, leaving more than 64 million tiny floating particles per square kilometer in certain areas, including plastic microfibers. In fact, of all the world’s major oceanic basins, the Mediterranean has the highest concentration of microfibers. These tiny synthetic strands are released by sources like fraying fishing nets, textile manufacturers, or loads of laundry . She says that it is one of the most common types of microplastics in the oceans. According to the study, the high salinity and density in Mediterranean waters could also lead to higher concentrations of fibers floating near the surface.

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Across the world’s oceans, plastic pollution has created a new artificial community for marine microbes–which researchers call the “plastisphere.” Free-floating bacteria and other microbiota can secrete sticky molecules that help them latch on to substrates, like wood, microalgae, or sediment. Once attached, the bacteria produce more of these sticky molecules to allow even more microbes to glom on, causing a biofilm to grow, Karen Shapiro, an infectious disease expert at the University of California, Davis, explained in an email to PopSci. Lacerda explains that plastics last longer than natural substrates in marine environments. This increases the risk of microbial contamination. Some plastics are lighter than seawater and can float on the ocean’s surface, where they can be carried far by currents.

” The plastic acts like a boat to these organisms,” Lacerda says. “They transport species across areas, which could lead to changes within the function of nature.”

Plastics can smell like food when they are colonized by bacteria. This could be dangerous for marine wildlife who might mistakenly eat them. Not only does that mean the microplastics work their way through the food chain, past studies have shown that toxic chemicals in plastics could provoke hormonal dysfunctions that affect growth and reproduction in some wildlife groups, including orcas and oysters.

microscopy photos of microfibers, revealing tiny bacteria and microbes on the surface
Photomicrograph of floating fibers collected from the coastal zone of the northwestern Mediterranean (A), and scanning electron microscopy (SEM) images of their bacterial communities (B), with elongated and rounded cells as well as the sticky molecular compounds that build biofilms (C-F). Pedrotti et al., 2022, PLOS ONE

To determine what kind of bacteria microfibers may harbor in the Mediterranean Sea’s northwestern end, Lacerda and her collaborators collected samples near Nice, France and Monaco, France. After identifying the microfibers, Lacerda and her colleagues used DNA sequencing and microscopy to identify the bacteria species and compare them to the free-floating bacteria found in the water. Among the 195 species living on the microfibers, Lacerda and the authors flagged a “great quantity” of pathogenic Vibrio parahaemolyticus, a bacteria that can cause seafood poisoning in humans.

Previous studies have found pathogenic marine microorganisms on plastics in the ocean, such as Aeromonas salmonicida, which can infect and kill salmon, and Arcobacter species, which can cause illness in people. “In one particular sample, the authors found nearly a third of the bacteria species to be V. parahaemolyticus, which is a notable proportion and of possible concern given its pathogenic potential,” Shapiro, who was not involved in the recent research but has also studied the plastisphere, wrote in her email. “These anthropogenically derived fibers that end up in our oceans could mediate disease transmission for sea life but also people that consume shellfish that can concentrate these contaminants.” V. parahaemolyticus thrives in warm brackish waters where filter feeders like oysters are typically cultivated.

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Knowing where microfibers and the harmful species they carry can help people determine if certain bodies are safe for swimming, farming, fishing, or bathing. Climate change could further the spread and pathogenicity of plastic-dwelling microorganisms that are influenced by temperature, including V. parahaemolyticus. “As the temperature of the ocean is increasing, the virulence and [plastic] adhesion of the organism also increases with the increase in temperature,” Lacerda says. This is especially important in a sand-locked sea like the Mediterranean, which is warming faster than other regions in the world. Lacerda says that this means that “we could expect the plastisphere of the Mediterranean Sea to respond faster to climate changes.”

According to Shapiro’s study in the Mediterranean, it adds to the growing body evidence that marine bacteria thriving upon plastic waste is “a global phenomenon which deserves more attention.” To better understand how humans alter and harm marine ecosystems, more research needs to be done on the interactions between pathogens.

” I believe that the public should be aware that plastic pollution in oceans doesn’t only affect marine wildlife but can also affect us,” Lacerda states. She says that as the plastic problem continues growing, it is important to find a new way to live .”

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