Exposed to plastic waste, the bacteria are “strongly” impaired in their capacity to grow and photosynthesize.

Plastic pollution has been harming marine creatures large and small, from giant whales to minute bacteria. We care about the whales, but we should also start caring about the bacteria.

“We found that exposure to chemicals leaching from plastic pollution interfered with the growth, photosynthesis and oxygen production of Prochlorococcus, the ocean’s most abundant photosynthetic bacteria,” says Sasha Tetu, a researcher at Macquarie University in Australia who was the lead author of a new study of the effects of plastic pollution on a species of photosynthetic marine bacteria.

Prochlorococcus bacteria are abundant in the oceans where they serve a vital function in global carbon recycling and produce a tenth of the oxygen that land animals like ourselves breathe. These green microbes are the most common photosynthetic organisms on Earth and are key to marine ecosystems owing to their production of carbohydrates and oxygen.

However, when they are exposed to plastic leachate from common waste items like polyethylene bags, millions upon millions of which are marinating in the oceans, the bacteria are “strongly” impaired in their capacity to grow and photosynthesize, say the scientists. They discovered this after they exposed strains of the bacteria to plastic waste in laboratory conditions in the first study of its kind.

“The strains [examined] showed distinct differences in the extent and timing of their response to each leachate,” they explain. “Consequently, plastic leachate exposure could influence marine Prochlorococcus community composition and potentially the broader composition and productivity of ocean phytoplankton communities.”

Exposure to plastic products like grocery bags and PVC matting limits the microbes’ ability to produce oxygen effectively. It even alters the expression of a large number of their genes. “Our data shows that plastic pollution may have widespread ecosystem impacts beyond the known effects on macro-organisms, such as seabirds and turtles,” Tetu says.

“If we truly want to understand the full impact of plastic pollution in the marine environment and find ways to mitigate it, we need to consider its impact on key microbial groups, including photosynthetic microbes,” the researcher adds.