Comparative secretome dynamics of Beauveria bassiana under solid-state and submerged fermentation

• First comparative secretome analysis of B. bassiana under SF vs SSF. • LC-MS/MS proteomics reveal metabolic versatility of B. bassiana . • Distinct CAZyme secretion highlights adaptation to fermentation modes. • Insights into B. bassiana enzymes and biomass valorisation applications. Beauveria bassiana (Bb) is a fungal entomopathogen that is popular in the industry as a biopesticide. Recently, some Bb strains have been demonstrated to have the ability to produce lignocellulose-degrading enzymes. Hence, to explore this fungus beyond its biocontrol applications - especially in bioprocesses which may involve its lignocellulolytic machinery- its differential secretome response to lignocellulosic biomass degradation under submerged fermentation (SF) and solid-state fermentation (SSF) conditions was evaluated for the first time using a Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) based approach. Initially secreted Bb proteins under the two conditions were harvested, and subjected to LC-MS/MS. Subsequently, the differential expression of the proteins was analysed while their carbohydrate-active enzymes (CAZymes), functional and gene ontology were annotated. Results revealed that the Bb secretome contained 613 (40 upregulated) and 1162 (301 upregulated) proteins during SF and SSF cultivations, respectively. Approximately 70 % of the proteins were identified with the general secretory (Sec) pathway, while showing low probabilities of being transmembrane proteins. The secretomes were principally composed of carbohydrate-active enzymes (CAZymes), proteases, metabolic proteins and structural proteins. Gene ontology also highlighted biomass deconstruction, facilitated by the plethora of Bb CAZymes as well as its proteases, as a prominent metabolic activity in the secretomes. Biological processes, such as microtubule cytoskeleton organisation, the glucan and cellulose catabolic process, as well as the carbohydrate metabolic process, were observed to be more pronounced in SSF relative to SF. The 147 and 236 CAZymes annotated during SF and SSF cultivation were observed to act on a wide range of polysaccharides, including cellulose, starch, xylan, lignin, chitin, and peptidoglycans. Hence, these findings demonstrate the higher complexity of Bb lignocellulose degradation under SSF relative to SF, thus further highlighting Bb as a model entomopathogen with potential in biomass pretreatment for biofuel production and the production of important enzymes for biomass valorisation and other sustainable bioprocesses.