Plastic bottles dominate the trash in the ocean, with around 3 feet of them reaching the sea every minute. Polyethylene terephthalate (Pet) bottles are the main culprit.
Last month, a study found two bacteria capable of breaking down Pet – or, as the headlines say, “eating plastic”. Known as Thioclava sp. BHET1 and Bacillus sp. BHET2, the bacteria were isolated in the lab – but they were discovered in the ocean.
Bacteria are the latest example of new organisms that seem to thrive in a unique environment: the large amounts of plastic in the sea.
Like the atmosphere, the magnetosphere and the hydrosphere, the plastisphere is a region. But it is also an ecosystem, like the Siberian steppe or coral reefs – a plasticized marine environment. The best-known concentration of marine plastic waste is the Greater Pacific Litter Pan, a kind of plastic soup spread over an area about twice the size of France, but plastic is everywhere.
First described in a 2013 study to refer to a collective of organisms colonizing plastic, including bacteria and fungi, the term has since broadened. It now loosely encompasses larger organisms, from crabs to jellyfish, which raft the oceans on marine plastics.
The term was coined by Linda Amaral-Zettler, a marine microbiologist at the Royal Netherlands Institute for Marine Research.
âIn 2010, we planned to collect plastic samples for an upcoming cruise to characterize the biofilms [organisms that stick to each other and other things] on plastic, âexplains Amaral-Zettler. âI was trying to find a practical term to describe the community and I found [â¦] ‘plastisphere’.
Although the term is recent, the phenomenon is not. âThe plastisphere has been around as long as plastic has existed,â says Amaral-Zettler.
What is new is our understanding of the complexity of the ecosystem that the world of plastics can be. In the plastisphere, there are organisms that do photosynthesis; there are predators and prey; symbionts and parasites, allowing “a full range of possible interactions, as in other ecosystems”, explains Amaral-Zettler.
“If we take the definition of an ecosystem as” a biological community of interacting organisms and their physical environment “then this is almost certainly true of the plastisphere,” says Robyn Wright, of the Department of Pharmacology at the Dalhousie University in Canada, and author of the June study.
Another unique feature of the plastisphere is that humans invented it. All other ecosystems have evolved over millions of years. The meaning of this is not yet clear.
“I don’t think it’s necessarily important that it’s not of natural origin, because all members of the plastisphere are still ‘natural’, but it’s more a matter of scale,” says Wright. Unlike most natural materials, plastic is very durable and persistent, allowing the growth and spread of attached organisms over a wide area.
In addition, a study last year found that certain colors of plastic affected the diversity of microbes that colonized them: communities on blue microplastics had richer diversity than those on yellow or transparent plastics.
There are also concerns about plastic colonizing organisms that can travel around the world. The Amaral-Zettler study in 2013 found Vibrio, a type of bacteria known to contain several species of pathogens, some associated with gastroenteritis.
While there is a potential for the plastisphere to harbor pathogens, Wright is skeptical. “There isn’t really any hard evidence that plastics pose more of a danger than any other surface colonized by bacteria, or any other area in the environment,” she says.
For scientists, the mere presence of the plastisphere is of less obvious concern than its potential health dangers. Most plastics end up in landfills, but almost a third ends up in the sea. The majority sink, but many don’t, becoming hotbeds for all kinds of germs that might not otherwise have a home. .
Bacteria move around because when plastics are submerged in water, they attract carbon, iron, nitrogen, and phosphorus, which in turn attract microbes. This is sometimes called the Zobell effect, named after marine microbiologist Claude E ZoBell.
What happens then is largely unknown.
âThis is still a very active area of ââresearch today,â says Wright. There are two main areas of investigation: potential pathogens in the plastisphere and the potential of certain microbes to biodegrade hydrocarbons, such as the plastic eaters identified last month.
These are not unique to the ocean. In 2016, Japanese scientists discovered Ideonelle sakaiensis, a species of bacteria in a landfill that had developed an enzyme that allowed it to eat plastic.
Corn another study the same year found that, compared to bacteria in the surrounding waters, those in the plastisphere possessed an enriched collection of genes, suggesting that they had adapted to a âlifestyle attached to the surfaceâ.
Scientists warn that it is important not to view them as recent mutants.
âWhile plastics are a relatively new material on an evolving timescale, the chemicals from which they are made are not new – primarily constituents of petroleum,â says Wright. “Bacteria have therefore had millions of years to develop mechanisms to break down the chemicals they are made of.”
Could the plastisphere evolve in such a way that bacteria essentially eat it, or at least help us identify ways to break down our plastic waste? “I would certainly agree that [microbes on] plastics are going to be the key place to look in the fight against plastic, âsays Wright.
But while Amaral-Zettler admits that some microbes may indeed feed on plastic already degraded by UV, she cautions against exaggerating the possibilities.
âIt’s important to realize that studies examining bacteria that eat plastic only provide these bacteria with a single source of carbon,â she says. âIt contrasts with what we find in nature. “
Laboratory studies also do not take into account ocean conditions, Wright says, such as different temperatures, weather conditions, or the presence of other organisms. “But,” she adds, “even just knowing that this is theoretically possible is a very big step in the right direction.”
Just like our own gastrointestinal microbiome, which is extremely important to our overall health, the plastisphere microbiome also has âan important role to play,â says Amaral-Zettler. Since we have altered our planet to the extent that these microbes have evolved to adapt to our plasticized oceans, it is crucial to understand the new ecosystem that we seem to have accidentally created.
âFor better or for worse, like plastic,â she says, âthe plastisphere is here to stay. “