Efficient production of Al(OH)3-immobilized laccase with aHeterobasidion annosumstrain selected by microplate screening

Abstract

Wild-type white rot fungi are the most important production organisms for laccase, a promising oxidative biocatalyst with numerous applications. This study aimed at identifying novel highly productive strains, finding optimal cultivation conditions for laccase production and establishing a simple immobilization procedure. By using a newly developed 96-well microplate cultivation method, 23 species of white rot fungi, represented by 29 strains, were directly compared with regard to the amount of secreted laccase. Both, with glucose and spruce saw dust as growth substrate a Heterobasidion annosum strain and a Physisporinus vitreus strain were the most productive (730–2200 U l−1 of secreted laccase). Cultivation conditions for laccase production with H. annosum were optimized in larger-scale liquid cultures. Aeration with a sparger lead to a 3·8-fold increase in laccase activity when compared to nonaerated flask cultures. More than 3000 U l−1 laccase was produced in glucose medium supplemented with yeast extract and the inducer veratryl alcohol. Culture supernatant was incubated with short-range ordered Al(OH)3 particles to directly immobilize and concentrate laccase by adsorption. Active laccase was recovered in 40% yield and the Al(OH)3-adsorbed laccase was suitable for repeated decolourization of indigo carmine. Microplate cultivation allowed a large-scale comparison of the capacity of different fungal species for laccase production. Laccase secretion of a highly productive H. annosum strain was found to vary strongly with different cultivation conditions. Adsorption to Al(OH)3 proved to be suitable as direct immobilization technique.