A novel acid-stable intracellular laccase from Aureobasidium pullulans: Purification, characterization and application in the removal of Bisphenol A from solutions

Abstract

A purified thermostable intracellular laccase obtained from the mycelia of Aureobasidium pullulans ( iLAp ) was deployed in the biodegradation of bisphenol A (BPA), an endocrine-disrupting compound. iLAp , a 61 kDa monomeric protein, has an of optimal pH and temperature of 3.0, and 50 °C respectively with 2, 2-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid] (ABTS) as substrate. iLAp was stable at these optimum pH and temperature for 6 and 8 h respectively retaining about 79 and 80% activity respectively. The k m ( 90.7 μ M ) , k c a t ( 35.7 s − 1 ) and k c a t k m ( 0.39 μ M − 1 s − 1 ) values obtained for iLAp, indicated it was more specific for ABTS than pyrogallol, guaiacol, and catechol. iLAp was stable in 10%v/v DMSO, methanol, and DMF. Metals such as Cu 2+ , Ca 2+ , and Mg 2+ enhanced laccase activity. Thioglycolic acid, dithiothreitol, sodium azide, and SDS strongly inhibited the laccase activity. The values of the kinetic/thermodynamic parameters obtained for iLAp such as: D-value (7302 and 2865 min), t 1 / 2 ( 2198 a n d 862 m i n ) Δ H d ( 67.5 a n d 67.4 k J m o l ) , Δ S d ( − [ 89.4 a n d 89.1 ] J / m o l / K ) and Δ G d ( 94.6 a n d 95.3 k J m o l ) indicated resistance to thermal inactivation at 40–50 °C respectively. iLAp was able to biodegrade BPA and the biodegradation efficiency significantly increased (p < 0.05) in the presence of ABTS as a mediator. From the GI values, the iLAp -treated BPA showed mild/no phytotoxicity towards Sorghum bicolor. • Presence of an intracellular, acid-stable laccase A. pullulans . • Laccase was stable against 10% water-miscible organic solvents. • The purified laccase was stable against heat inactivation at 40-50 °C. • Laccase removed BPA from solutions. • Laccase-treated BPA solutions showed no phytotoxicity towards S. bicolor seeds.