Polymer substrate reshapes the microbial assemblage and metabolic patterns within a biofilm denitrification system

A thorough heterotrophic denitrification process is difficult to complete when the carbon source is insufficient. The use of solid, biodegradable polymers to enhance denitrification is a promising solution due to their continuous carbon release characteristics and their safety advantages. However, the community succession and metabolic patterns in the polymer-based denitrification system still remain largely unclear, and few studies have investigated the polymer's carbon release rate in detail. In this study, we developed a biofilm denitrification system using biodegradable polycaprolactone (PCL) as an external carbon source, and present a novel stoichiometric approach that allows quantitative assessment of the polymer's carbon release rate. The results unequivocally demonstrate the coexisting ecological assemblages and coupled metabolic patterns of polymer degradation and denitrification in the system. Furthermore, as a result of the polymer substrate's pressure selection, the dominant denitrifying bacteria has been replaced by Acidovorax, which is capable of metabolizing polyester. Finally, the metabolic pattern of PCL degradation coupled with nitrate reduction was established according to the functional enzymes. By applying biochemical and ecological theories, this work promotes both a comprehensive understanding of the ecological-metabolic patterns in polymer enhanced denitrification systems and the methodological capability to estimate carbon release rates in engineered environments.