Plastic Pollution Boosts Bacterial Growth in Lake Water

Plastic pollution has gained widespread attention over the years due to its negative effects on both living systems and the environment. Among other ills, plastics contribute to changes in the climate from the time they are produced to their eventual disposal, and have even been found in human placentas. But for certain lake-dwelling bacteria, at least, the rise in plastic pollution appears to be welcome. In a study published today (July 26) in Nature Communications, researchers at the University of Cambridge in the UK show that plastic-infused water can supercharge the growth of these bugs.  

The researchers simulated plastic leachate—a mixture of chemicals that washes off plastics—in the lab by cutting up plastic shopping bags made of low-density polyethylene and incubating them in distilled water for seven days. They shook it continually to mimic natural forces in the environment. They then filtered out the solid particles, leaving organic molecules, some of which were not found naturally in lake water. They then introduced the solution into water samples collected from 29 Scandinavian lakes. The researchers report that this plastic leachate more than doubled the bacteria population in each sample.  

Young woman sitting on box in gravel parking lot with foil-wrapped bottles and small test tubes

Eleanor Sheridan collecting samples

Samuel Woodman

Evolutionary biologist Eleanor Sheridan of Uppsala University in Sweden, who participated in the study while an undergraduate student at Cambridge, tells The Scientist that the leachate boosted the bacteria’s protein production and also caused them to efficiently degrade carbon compounds that had already been present in the water, but they are not sure why. However, she says the plastic leachates contained a large number of compounds that are easy for bacteria to break down and consume, and this could explain the bacteria’s response to it.  

Victor de Lorenzo, an environmental microbiologist at the Spanish National Research Council who was not involved in the study, tells The Scientist that the ability of bacteria to use “compounds that have not existed before in the biosphere” as food is “very good news. . . . It means that in the biosphere, there’s so far [an] untapped ability to degrade plastics that we know very little about, and that’s a kind of a hopeful bit of information.” 

The team also observed that the microbes in lake samples responded differently to the presence of the leachate. That is, bacteria in samples with an initially low concentration of dissolved organic matter responded with more growth than did those with high concentrations of this matter. “Whether there was an increase in efficiency with plastics addition actually depended on the carbon that was already present in the lake, not just the added carbon from the plastic,” says Sheridan. “It might be that adding this carbon has created more new niches for bacteria to exploit.”  

De Lorenzo says the findings are “very interesting,” but adds that he expected more details about which type of bacteria acted on each chemical in the leachate. “In medical microbiology, you need to identify the pathogen for a specific disease. In the case [of] environmental microbiology, it [is] very important to identify what specific bacteria is degrading what specific molecule,” he says.  

While Sheridan and her colleagues did not drill down to that level of detail, they did analyze the microbial communities present in the sampled lakes and the groups that grew the most in the presence of the leachate: the genera Hymenobacter and Deinococcus. A previous study by a different group had also found that Hymenobacter and Deinococcus could break down biodegradable plastics in the environment. 

Sheridan notes that the team’s findings point to the effects of plastic leachates on the natural order of freshwater organisms, with implications for aquatic food webs. “If plastics are promoting growth of certain groups of bacteria, this could disrupt the balance of species and change the balance of bacteria in the ecosystem,” says Sheridan. “It could quite easily have implications on other parts of the food web.”

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