Comparative secretome analysis of T. reesei and A. niger using a novel sequential cultivation method for the cellulase production

New bioprocesses for enzyme production applied in the bioconversion of lignocellulosic material to fermentable sugars are needed to reduce costs and improve the efficiency of enzyme cocktails. Trichoderma reesei and Aspergillus niger are the most studied cellulolytic strains. The aim of this study was to characterize by proteomic analysis the variation for both strains of secretome composition in conventional submerged fermentation (SmF) and novel solid-state and submerged sequential fermentation (SF) cultivations using pretreated sugarcane bagasse as carbon source. SF process was more effective than SmF for the two strains tested for enzyme production and when using cellulolytic enzymes at the same loading for hydrolysis of sugarcane bagasse. Xylanase and β-glucosidase activities increased up around 3-fold (T. reesei, A. niger) and 8-fold (A. niger) when using SF. The enzymatic hydrolysis performed with SF extract resulted in cellulose conversion 2.5 times higher than SmF. Proteomic analyses of samples derived from both fermentation approaches were performed. Growth of the T. reesei strain in SmF resulted in the secretion of 97 protein groups (versus 79 identified in samples from SF) of which 51 were exclusively identified in this cultivation method (versus 33 from SF). In the secretome produced by A.niger in SmF and SF, 99 and 112 protein groups were identified, respectively, of which 37 were unique to SmF and 55 to SF methods. Additional endoglucanases and β-glucosidases observed in the secretome of A. niger cultivated under SF approach may help to explain the higher cellulose conversion results obtained for hydrolysis of sugarcane bagasse.