Removal of sulfamethoxazole and production of cyanobacterial lipid promoted by the construction of a consortium containing a non-toxic cyanobacterium and sewage bacteria

Abstract

This study evaluated the possibility of constructing a consortium containing sewage bacteria and cyanobacterial cells immobilized by Ca-alginate for the advanced treatment of antibiotic-polluted sewage coupled to cyanobacterial lipid production. Two non-toxic cyanobacterial species (Synechococcus sp. and Chroococcus sp.) were exposed to 0.5–20.0 μg/L of sulfamethoxazole (SMZ) for 4 days. Comparison between suspended and immobilized conditions indicated that immobilization increased (p < 0.05) SMZ removal percentage without reducing cyanobacterial growth performance (indicated by OD680), chlorophyll-a content, dry cell weight, lipid content and lipid weight/productivity of each cyanobacterium. Chroococcus sp. presented better antibiotic removal and lipid production ability than Synechococcus sp. After the addition of immobilized Chroococcus sp. into sewage, sewage bacteria attached to the surface and filled the pores of cyanobacterial beads. Immobilized Chroococcus sp. promoted the succession of sewage microbial community towards the dominance of Cellvibrio, Flavobacterium, Formivibrio and Pseudomonas, which participated in denitrification, phosphate accumulation and antibiotic removal. In the sewage microbial community, various functional genes upregulated by immobilized Chroococcus sp. directly showed negative correlation (p < 0.05) with sewage contaminants, including gltB, glnA and napA responsible for nitrogen removal; pstS responsible for phosphorus removal; nqrF, cbhA, glgC, malZ, pulA, uxaA and maeA responsible for COD removal; frmA, katG, maeA, uxaA, carB and cbhA responsible for SMZ removal. Coexisting sewage bacteria elevated (p < 0.05) lipid productivity of immobilized Chroococcus sp. to 29.13–36.52 mg/L/day through the upregulation of various genes related to metabolite exchange and signal transduction. Cyanobacterial cells degraded SMZ in collaboration with sewage bacteria, through deamination, nitration, bond cleavage, hydroxylation, desulfonation and nitrosation. The cyanobacteria-bacteria consortium presented 4-day removal percentages of 54.58–68.39%, 66.14–68.69%, 95.77–96.31% and 81.09–82.35% for SMZ, TN, TP and COD, respectively. In general, the cyanobacteria-bacteria consortium achieved a good combination of cyanobacterial lipid productivity and sewage treatment efficiency.