Among seven carbon sources tested, glycerol and glucose favored theCerrena unicolorlaccase production (18.8-20.3 U/mL); in addition, glycerol ensured the highest manganese peroxidase (MnP) activity (2 U/mL). Substitution of glycerol with the ethanol production residue (EPR) gave the highest laccase (90.1 U/mL) activity, while the walnut pericarp provided the highest MnP activity (7.4 U/mL). Supplementation of medium with 1 mM copper and 1 mM xylidine at appropriate time caused significant additive effect on laccase expression (333.2 U/mL) in shake-flask experiments. Overproduction of laccase activity (507 U/mL) and secretion of MnP activity was obtained whenC. unicolorwas cultivated in stirred-tank fermenter.C. unicolorshowed several distinctive and attractive technological features: it is capable to synthesize high levels of oxidases under high carbon and high nitrogen conditions and it secretes high laccase activity during trophophase.

In the present study, the polysaccharide-hydrolyzing secretomes of Irpex lacteus (Fr.) Fr. (1828) BCC104, Pycnoporus coccineus (Fr.) Bondartsev and Singer (1941) BCC310, and Schizophyllum commune Fr. (1815) BCC632 were analyzed in submerged fermentation conditions to elucidate the effect of chemically and structurally different carbon sources on the expression of cellulases and xylanase. Among polymeric substrates, crystalline cellulose appeared to be the best carbon source providing the highest endoglucanase, total cellulase, and xylanase activities. Mandarin pomace as a growth substrate for S. commune allowed to achieve comparatively high volumetric activities of all target enzymes while wheat straw induced a significant secretion of cellulase and xylanase activities of I. lacteus and P. coccineus. An additive effect on the secretion of cellulases and xylanases by the tested fungi was observed when crystalline cellulose was combined with mandarin pomace. In I. lacteus the cellulase and xylanase production is inducible in the presence of cellulose-rich substrates but is suppressed in the presence of an excess of easily metabolizable carbon source. These enzymes are expressed in a coordinated manner under all conditions studied. It was shown that the substitution of glucose in the inoculum medium with Avicel provides accelerated enzyme production by I. lacteus and higher cellulase and xylanase activities of the fungus. These results add new knowledge to the physiology of basidiomycetes to improve cellulase production.

The potential of wood-rotting and litter-deconstructing basidiomycetes to convert lignocellulose into a wide variety of products has been extensively studied. In particular, wood-rotting basidiomycete secretomes are attracting much attention from researchers and biotechnology companies due to their ability to produce extracellular hydrolytic and oxidative enzymes that effectively degrade cellulose, hemicellulose, and lignin of plant biomass. An analysis of the available literature data shows that Basidiomycota fungi, which are most adapted to the depolymerization of plant polysaccharides, are promising but so far unexploited sources of new hydrolytic enzymes. The review summarizes the latest data on the great variety, common features, and unique properties of individual fungi and the production of cellulases and xylanases by various physiological and ecological groups of basidiomycetes. The most important microbial cellulase-producing strains for submerged and solid-phase fermentation, as well as the main substrates, including the use of agro-industrial waste, are considered. It highlights ways to increase both cellulase and xylanase expression levels and the cost-effectiveness of producing these enzymes for various biotechnological applications. It is anticipated that this review will be particularly useful to novice scientists working in the lignocellulose biorefinery, as it describes current knowledge and issues related to the production and regulation of polysaccharide hydrolyzing enzyme synthesis.

This study aimed to characterize the cellulolytic system of Irpex lacteus BCC 104 isolated from the forest of Georgia. The results obtained showed that the expression of endoglucanase and xylanase synthesis in this fungus is inducible in the presence of cellulose-containing growth substrates. Among them, crystalline cellulose appeared to be the best carbon source providing the highest endoglucanase (48.0 U/mL), total cellulase (7.6 U/mL), and xylanase (68.4 U/mL) activities. Supplementation of the Avicel-induced culture with 0.5 or 1% glycerol caused catabolite repression of the cellulase and xylanase formation by I.lacteus BCC 104. The enzyme synthesis resumed only after the depletion of easily metabolizable carbon source from the medium. The crude enzyme obtained after the cultivation of I. lacteus in the fermenter and used for saccharification of pretreated wheat straw (40 mg/mL, FPA load 20 U/g substrate) yielded 10.7 mg reducing sugars/mL (32.2% from the theoretically possible). CMCase and xylanase were purified 31- and 34-fold and characterized. The optimum pH for both enzyme activities was found to be 5.0; at pH 5-6, they retained 60% of their initial activity after incubation at 30°C for 48 h. CMCase expressed maximum activity at 50°C while xylanase – at 55°C. Half-inactivation periods of endoglucanase and xylanase during incubation at 60°C were 60 min and 150 min, respectively.