Substrate-specific microbial community shifts during mesophilic biodegradation of polymers in compost amended soil

Plastics are widely utilized across various industries, but their persistent accumulation in the environment has become a major ecological concern. Biodegradable alternatives offer a potential solution to plastic pollution; however, their degradation behavior under environmentally relevant conditions remains underexplored. This study evaluates the aerobic biodegradation of four polymer materials: starch, commercial thermoplastic starch of polyester origin (TPS1), linear low-density polyethylene (LLDPE), and a co-polyester thermoplastic starch (TPS2), over 180 days at 25 °C in a compost-soil matrix using the testing protocols of ASTM D5988-18 for carbon dioxide (CO₂) evolution. Microbial community dynamics were profiled using 16S rRNA and ITS2 amplicon sequencing. TPS2 reached complete mineralization (~ 100%) in 28 days, followed by starch at 71.1% by day 180. TPS1 showed partial mineralization of 38.6%, while LLDPE showed minimal mineralization (21.9%) as expected. Alpha diversity revealed higher bacterial richness in starch treatments and a marked reduction in fungal diversity in TPS1 and LLDPE. Differential abundance testing revealed significant microbial shifts between treatments. Linear discriminant analysis Effect Size (LEfSe) identified polymer-specific microbial biomarkers, including Paenibacillus and Botryotrichum for starch, Acrophialophora and Mycothermus for TPS2, and the Mycobacterium for LLDPE. Subgroup 10 Acidobacteria was uniquely enriched in TPS2-treated samples. These taxa reflect substrate-driven microbial selection. Coupling CO₂ mineralization with microbial profiling offers a practical framework to evaluate polymer biodegradability and guide the design of soil-degradable bioplastics. Overall, these findings demonstrate that polymer composition significantly influences microbial community structure and mineralization performance under mesophilic conditions.