Characterization of the secretome of Aspergillus brasiliensis during sucrose metabolism in solid-state and submerged fermentations.

Diverse studies have indicated that fungal growth and enzyme yields are often greater in solid-state fermentation (SSF) than in submerged fermentation (SmF). To understand the advantages of SSF over SmF, the secretomes of Aspergillus brasiliensis cultured with different sucrose concentrations were analyzed. Secretomic analysis revealed that sucrose induced the production of several polysaccharide-degrading enzymes, and that the secretome of SSF was more complex. Approximately 90% of the secreted proteins in SmF were via signal peptide-mediated mechanisms. However, increasing the sucrose concentration in SSF reduced this to less than 50%, suggesting the presence of alternative secretion mechanisms. Protein fold-change analysis revealed that certain proteins were induced by high sucrose in both cultures. Nevertheless, the relative abundance (RA) was higher under SSF. The production of some extracellular enzymes in both culture types confirmed the absence of catabolic repression mainly in SSF, where invertase and inulinase production were 1.5 and 2.1-fold higher than in SmF, respectively. Thus, SSF provides an environment that facilitates A. brasiliensis growth with minimal constraints from catabolite repression or substrate inhibition. This is due to the diversity of proteins secreted through both conventional and unconventional mechanisms, highlighting the similarity of SSF to the natural fungal habitat.