Enhanced enzyme production with the pelleted form of D. squalens in laboratory bioreactors using added natural lignin inducer

Abstract

White-rot fungi are extensively used in various submerged biotechnology processes to produce ligninolytic enzymes. Transfer of the process from the laboratory to the industrial level requires optimization of the cultivation conditions on the laboratory scale. An interesting area of optimization is pellet growth since this morphological form solves problems such as the decreased oxygen concentration, limited heat, and nutrient transport, which usually occur in dispersed mycelium cultures. Many submerged fermentations with basidiomycetes in pellet form were done with Phanerochaete, Trametes, and Bjerkandera species, among others. In our study, another promising basidiomycete, D. squalens, was used for ligninolytic enzyme production. With the addition of wood particles (sawdust) as a natural inducer and optimization of mixing and aeration conditions in laboratory stirred tank (STR) and bubble column (BCR) reactors on pellet growth and morphology, the secretion of laccase and the manganese-dependent peroxidase into the medium was substantially enhanced. The maximum mean pellet radius was achieved after 10 days in the BCR (5.1 mm) where pellets were fluffy and 5 days in the STR (3.5 mm) where they were round and smooth. The maximum Lac activity (1,882 U l(-1)) was obtained after 12 days in the STR, while maximum MnP activity (449.8 U l(-1)) occurred after 18 days in the BCR. The pellet size and morphology depended on the agitation and aeration conditions and consequently influenced a particular enzyme synthesis. The enzyme activities were high and comparable with the activities found for other investigations in reactors with basidiomycetes in the form of pellets.

Fungal pelleted reactors in wastewater treatment: Applications and perspectives

“…Under optimal mixing conditions, the STR has shown to promote and enhance the production of certain fungal enzymes. Babiĉ and Pavko [79] observed an increased production of laccase by pellets of the white-rot fungus, Dichomitus squalens, when cultivated under optimal conditions in a STR with a natural inducer (saw dust). The laccase production was higher than those obtained when incubated in a bubble column reactor.…”

Process Parameters Affecting the Synthesis of Natural Flavors by Shiitake (Lentinula edodes) during the Production of a Non-Alcoholic Beverage

“…This result shows that the pellets were damaged by the mechanical forces created in stirred tank bioreactor. It is generally observed that the pellet size decreases with increasing agitation intensity, which is related to mechanical shear forces [20,21]. It was reported that higher shear forces created in stirred tank bioreactor can destroy the hairiness of the fungal pellets [22].…”

“…Smaller and less compact pellets were formed at the highest agitation rate of 300 rpm [20]. Mild agitation rates are preferable for laccase production by Dichomitus squalens and Pleurotus ostreatus in stirred tank bioreactors [21,23]. The laccase production by Panus tigrinus on olive mill wastewater-based media was influenced negatively when the stirrer speed was increased [35].…”

“…The production of ligninolytic enzymes by D. squalens in a 3 L stirred tank bioreactor enhanced when the agitation intensity increased from 175 rpm (P/V: 20 W/m 3 ) to 250 rpm (P/V: 80 W/m 3 ). However, a further increase to an agitation intensity of 350 rpm (P/V: 180 W/m 3 ) led to a decrease in enzyme production [21]. Therefore, bioreactor systems with lower shear environment are sometimes preferable for the fungal metabolites.…”

“…Therefore, bioreactor systems with lower shear environment are sometimes preferable for the fungal metabolites. The production of a manganese-dependent peroxidase (MnP) by D. squalens was promoted when the fungus was cultivated in a bubble column reactor, which has lower shear effects than a stirred tank bioreactor [21]. Phenolic compounds in olive mill wastewater were also degraded more rapidly by Panus tigrinus in a bubble column bioreactor reflecting the production of larger amounts of the enzymes laccase and Mn (II) peroxidase [36].…”