Characterization of a thermostable and solvent-tolerant laccase produced by Streptomyces sp. LAO.

Abstract

Decaying wood samples were collected, and actinomycetes were isolated and screened for laccase production. The identity of the efficient laccase-producing isolate was confirmed by using a molecular approach. Fermentation conditions for laccase production were optimized, and laccase biochemical properties were studied. Based on the 16S rRNA gene sequencing and phylogenetic analysis, the isolate coded as HWP3 was identified as Streptomyces sp. LAO. The time-course study showed that the isolate optimally produced laccase at 84h with 40.58 ± 2.35 U/mL activity. The optimized physicochemical conditions consisted of pH 5.0, ferulic acid (0.04%; v/v), pine back (0.2g/L), urea (1.0g/L), and lactose (1g/L). Streptomyces sp. LAO laccase was optimally active at pH and temperature of 8.0 and 90°C, respectively, with remarkable pH and thermal stability. Furthermore, the enzyme had a sufficient tolerance for organic solvents after 16h of preincubation, with laccase activity > 70%. Additionally, the laccase maintained considerable residual activity after pretreatment with 100mM of chemical agents, including sodium dodecyl sulphate (69.93 ± 0.89%), ethylenediaminetetraacetic acid (93.1 ± 7.85%), NaN3 (96.28 ± 3.34%) and urea (106.03 ± 10.72%). The laccase's pH and thermal stability; and robust catalytic efficiency in the presence of organic solvents suggest its industrial and biotechnological application potentials for the sustainable development of green chemistry.