Optimized production of laccase from Pseudomonas stutzeri and its biodegradation of lignin in biomass

Laccases are multi-copper oxidases that play an important role in the biodegradation of phenolic compounds, lignin, dye, and wastes. Here, we report the screening of potential laccase-producing indigenous bacterial isolates and subsequent optimization of laccase production using crop residues as cheap supplementary energy sources. Among 16 bacterial isolates, seven were selected based on the appearance of reddish-brown bacterial colonies and guaiacol oxidation assay after 10 days of incubation at 37 °C. The maximum laccase activity (2.755 U/mL) was observed for bacterial isolate WR2. Response surface methodology (RSM) was used to maximize laccase production from WR2, identified as Pseudomonas stutzeri. Plackett-Burman design (PBD) was employed to design production runs involving various factors including time, pH, inoculum, wheat straw, cotton stalk, wheat bran, rice straw, copper sulfate, sugarcane bagasse, yeast extract, and peptone. The interactions of different factors were analyzed from the responses (laccase enzyme activity, etc.) in 12 experimental runs. In experimental run 4, the maximum laccase enzymatic activity (1.86 U/mL) was achieved after a 10-day incubation with wheat straw (1%) and cotton stalk (1%) at pH 6.8 and 37 °C, and high-degree lignin degradation was evident from a substantial reduction in the FTIR aromatic stretching peak of the degraded biomass.