Bioplastics spark viral activity, reshape microbiomes and accelerate organic matter degradation in the marine environment

Bioplastic and polylactic acid production is expected to increase in the future to replace single-use traditional plastics. Here we investigated the effects of polylactic acid contamination in marine ecosystems by assessing its degradation over time in an experimental mesocosm, along with its impact on microbial abundance, microbiome diversity, viral infections, and rates of organic matter cycling. We report here that, as polylactic acid gradually lost its integrity, a microbial biofilm rich in Marinobacter sp. developed on the biopolymer, reshaping the marine microbiome, promoting polylactic acid-associated bacteria such as the Saccharospirillaceae, and in turn increasing viral activity and accelerating the degradation of organic matter. These effects, which were further amplified at the temperatures experienced during heatwaves, suggest that high levels of polylactic acid contamination might influence the functioning of coastal marine ecosystems, particularly during extreme temperature episodes.