A synthetic community derived from marine microplastic biofilms for efficient nitrate removal

Abstract

Microbial communities on marine microplastics form a novel niche and can be explored for industrially useful strains, including those for wastewater denitrification. Here, we isolated three strains (P. stutzeri P5F4–3, Ruegeria sp. PMMA7, and Shimia sp. pe10) carrying complete denitrification gene clusters from subtidal microplastic biofilms and constructed a synthetic community (SynCom) with them. The SynCom exhibited high nitrate removal efficiency and stability under high salinity, with stable community composition. Metatranscriptomic analysis further indicated functional division of labor through differential metabolic reprogramming: P5F4–3 upregulated denitrification genes and stress response genes while downregulating energy metabolism and ribosome synthesis; PMMA7 specifically upregulated the entire nitrous oxide reductase gene cluster, focusing on the terminal denitrification step, while suppressing central carbon metabolism, nutrient uptake, and biosynthesis; pe10 enhanced ribosome biosynthesis, energy metabolism, and cofactor synthesis while simplifying nutrient uptake and motility-related pathways. In carrier colonization experiments, the SynCom formed biofilms and effectively removed nitrate without significant nitrite accumulation. Moreover, the nitrate removal efficiency was validated in a laboratory-scale moving bed biofilm reactor, supporting its potential for practical application. Collectively, these findings identify marine microplastic biofilms as a cultivable source of salt-tolerant denitrifiers and demonstrate the potential of defined SynCom for saline denitrification.