Exopolysaccharide of the dairy-wastewater isolate Escherichia sp. UW6: From RSM-driven yield enhancement to...

Dairy-effluent isolates were screened for EPS production based on mucoid colony morphology, phenol-sulphuric acid assay, and viscosity. UW6, identified as Escherichia sp. (99.06 % to E. marmotae HT073016(T)), produced 35.92 ± 2.85 μg/mg EPS with a viscosity of 1.18 ± 0.03 Pa·s at 72 h. Six-factor BBD EPS optimisation yielded a significant quadratic model (p < 0.0001) with strong fit (R² = 0.9982; adj R² = 0.9944; pred R² = 0.9677). Optimal conditions (pH 5.4, 38 °C, 138 h, 8.5 mL inoculum; sucrose-peptone) gave a predicted 68.56 μg/mg and an observed 67.52 ± 1.07 μg/mg (< 2 % deviation), confirming model validity. FTIR, 1D NMR, and HPLC identified the EPS as a heteropolysaccharide with a branched α-(1 → 3)-D-galactan backbone and β-(1 → 6)-d-glucopyranosyl side chains. SEM showed a rough, porous, largely amorphous surface; XRD indicated mixed crystalline-amorphous character. Elemental analysis (C- and O-rich) matched carbohydrate composition. The EPS carried a moderate negative charge (ζ = -14.2 mV) and formed ∼1.04 μm aggregates by DLS (90.9 % intensity). Functionally, EPS showed dose-dependent emulsification (35.83 ± 3.82 % in xylene at 1.0 mg/mL) and flocculation (87.81 ± 0.13 % at 100 mg/L). In wastewater, EPS removed 86 % sulphate and 85 % chloride; reduced BOD by >50 % (chemical/textile), TSS by ∼76 % (dairy/oil), and COD in oil/chemical effluents. Nitrogen decreased by 6.7-22.3 %, and pH shifted toward neutrality. These findings highlight that EPS is an eco-friendly alternative to chemical coagulants for wastewater treatment. This study confirms Escherichia sp. UW6 as a sustainable biopolymer source and advances microbial EPS applications for green remediation.