Sundarbans mangrove microbiota as agents for low-density polyethylene degradation

Low-Density Polyethylene (LDPE) accumulation in marine and terrestrial ecosystems poses a planetary crisis, requiring sustainable bioremediation. Existing microbial degradation studies are often limited by a reliance on abiotic pretreatments (e.g., UV or thermal oxidation) and terrestrial isolates that lack environmental resilience. To address this gap, this study investigates the biodegradation potential of novel lipolytic bacterial strains Bacillus tropicus SBAA01 and Pseudomonas aeruginosa SBAA02 isolated from the Sundarbans mangrove ecosystem, India; a UNESCO World Heritage Site & Ramsar wetland. The untreated LDPE films were incubated for 42 days under co-metabolic conditions. Upon benchmarking against a previously isolated reference strain, Bacillus pacificus SBAA07, B. tropicus SBAA01 emerged as the most potent candidate. It achieved a net dry weight loss of 13.63% ± 0.01 with a calculated half-life (t_1/2) of 198 days. Topographical analysis via Atomic Force Microscopy (AFM) revealed a significant 736% increase in surface root mean square roughness (Rq), correlating with deep pitting observed in Scanning Electron Microscopy (SEM). Conversely, P. aeruginosa SBAA02 showed significant surface disruption Rq value increase of 142% but lower weight loss efficiency of 8.89% ± 0.01. Critically, while B. tropicus SBAA01 drove the highest physical erosion; it maintained a moderate Carbonyl Index (CI) of 0.184. This suggests oxidative carbonyl intermediates are assimilated into biomass faster than they accumulate on the surface. These findings suggest the Sundarbans as a genetic reservoir for stress-tolerant biocatalysts capable of degrading pristine polymers without prior oxidation. This offers a scalable, nature-based solution for plastic waste management.