Plastisphere-isolated Stutzerimonas balearica SP-H sustains stable sulfur-autotrophic denitrification under...

Microplastic (MP) accumulation in constructed wetlands potentially threatens sulfur-autotrophic denitrification under low C/N conditions, yet the resilience of plastisphere-derived denitrifiers remains poorly understood. Here, we isolated and compared two denitrifying strains, a plastisphere isolate, Stutzerimonas balearica SP-H, and a conventional wetland isolate, Castellaniella denitrificans S0-H, under polyamide (PA) and polyethylene (PE) MP exposure. MPs severely impaired strain S0-H, causing nitrate removal inhibition (50.40-74.42%), nitrite accumulation (93.54-95.79%), elevated N₂O production (57.24-94.32%), and reduced sulfate generation (38.94-66.95%). In contrast, strain SP-H maintained efficient nitrate depletion and stable sulfur oxidation under MP stress. Mechanistically, strain SP-H's superior tolerance involved a coordinated multi-layered defense: higher activities of Nar, Nir, and Sox, upregulated c-di-GMP, enhanced polysaccharide-rich extracellular polymeric substances (EPS) production, and preserved ATP levels. Collectively, habitat origin may determine MP resistance, and plastisphere-isolated strains like SP-H represent promising bioaugmentation agents to stabilize sulfur-based autotrophic denitrification in MP-impacted wastewater systems.