One 'Biodegradable' Plastic Hit 99.9% Breakdown in 17 Days. Another Stalled at 2.7% in 320

Takeaway: under landfill-like conditions, the three "biodegradable" plastics behaved like three different materials.

Which microbes are actually doing the work?

The team then examined gene activity in the microbial communities on the plastics. They combined metagenomic analysis, which reads the DNA present, with metatranscriptomic analysis, which reads the RNA being produced — that is, which genes are actually switched on.

Of 238 reconstructed microbial genomes, 118 carried candidate genes encoding enzymes that might depolymerize PHB or PLA. But only 49 of those genomes showed evidence that those genes were being transcribed. Having the gene, in short, does not mean using it.

Many of the transcription-supported candidates belong to poorly characterized microbial lineages, beyond the known, experimentally validated plastic degraders in reference databases. That makes these lineages promising targets for finding new plastic-degrading microorganisms and enzymes.

The gene activity also concentrated in biofilms on the plastic surfaces rather than in the surrounding leachate. So researchers need to track not just which microbes are present, but what the ones attached to the plastic are actually doing.

Takeaway: the most interesting suspects are unfamiliar microbes living directly on the plastic.

How solid are the findings?

The caveats are real. Transcription of a candidate gene does not prove that the microorganism or enzyme actually degrades plastic; each candidate function needs validation in follow-up experiments. And the degradation figures came from laboratory incubations at a constant 35 °C, so they should not be read as predictions of real-world landfill rates, which depend on temperature, oxygen and local microbial communities.

The study's broader point survives those limits. Biodegradable plastics are often evaluated on material properties or labels alone, yet a plastic that vanishes in a hot composting plant can persist for a long time in a landfill — especially when separate collection systems fall short and these materials end up mixed with general municipal waste.

"Our findings show that biodegradability is not simply an inherent property of a plastic material, but also depends on the environmental conditions and microbial communities it encounters after disposal," Myung said.

"The substantial degradation of PLA under mesophilic anaerobic conditions was particularly surprising, highlighting the importance of understanding which microorganisms are active and what functions they perform," he added, expressing hope that the work will guide more environmentally relevant biodegradability assessments and the discovery of new plastic-degrading organisms.

The paper is Shinhyeong Choe et al., "Divergent anaerobic fates of biodegradable plastics in landfill leachate," Nature Communications (2026), DOI: 10.1038/s41467-026-78850-w.

Takeaway: a biodegradability label tells you what a plastic might do — the disposal environment decides what it actually does.