Light exposure reshapes microbial community assembly on plastic in Winogradsky columns

Plastic pollution in landfills presents a significant environmental challenge, as macroplastics fragment into persistent and harmful micro- and nanoplastics. Despite growing interest in plastitrophs, we know relatively little about how environmental conditions shape their community assembly and function. Among possible determinants, light exposure is likely consequential but remains poorly characterized. We examined how ambient light versus dark incubation conditions affect plastitrophic potential using 36 modified Winogradsky columns seeded with landfill soil from Portland, Connecticut United States of America. We incubated the columns with or without polyethylene (PE) sheets added, over 12 months, and we sampled across four stratified layers for 16S rRNA gene sequencing and targeted metagenomic analysis of PE strips. Light exposure promoted the enrichment of photoautotrophic Cyanobacteriota and Chloroflexota, while dark conditions favored anaerobic Bacillota and Bacteroidota. Metagenomic analysis revealed strong enrichment of light-responsive pathway genes, including circadian rhythm mechanisms, phototransduction, and pigment biosynthesis. In the replicated 16S dataset, species richness and Shannon diversity did not differ significantly between light and dark or between plastic and soil. Higher diversity under light appeared only in the smaller, exploratory metagenomic dataset (n = 3 per condition). Putative plastizyme genes, identified by name matching to curated databases, showed higher abundance under light, with oxidoreductases showing the strongest increase. Our findings reveal that light exposure enriches plastitrophic communities, light-responsive pathway genes and degradation-associated functional potential. This work provides foundational insight into how natural environmental factors such as light shape the genetic potential for oxidative transformation of polyethylene in terrestrial plastispheres.