Regulation in Metabolic Pathways Revealed Mechanisms of Polyacrylamide Degradation and Utilization by <i>Scenedesmus quadricauda</i> Cells

To treat polyacrylamide-containing oilfield wastewater in a green way, thick-walled and resistant Scenedesmus quadricauda cells were used to biodegrade and utilize polyacrylamide. Extracellular urease secreted by Scenedesmus quadricauda cells degraded polyacrylamide into poly(acrylic acid) and ammonia, which provided carbon and nitrogen sources for cell growth. Proteomics showed that metabolic pathways of ribosome synthesis and fatty acid oxidative decomposition were significantly downregulated, while those of amino acid synthesis and energy supply were significantly upregulated. This indicated that flocculation induced by polyacrylamide within 72 h inhibited gene transcription and proliferation, but biodegraded polyacrylamide after 72 h promoted biomass synthesis. 500 mg/L polyacrylamide was the most favorable concentration to biomass growth (with an increase by 15% to 2.4 g/L) and CO2 fixation for Scenedesmus quadricauda cells.