Abstract
Copper Radical Alcohol Oxidases (CRO-AlcOx), which have been recently discovered among fungal phytopathogens are attractive for the production of fragrant fatty aldehydes. With the initial objective to investigate the secretion of CRO-AlcOx by natural fungal strains, we undertook time-course analyses of the secretomes of three Colletotrichum species ( C. graminicola , C. tabacum and C. destructivum) using proteomics. The addition of a copper-manganese-ethanol mixture in absence of any plant-biomass mimicking compounds to Colletotrichum cultures unexpectedly induced the secretion of up to 400 proteins, 29-52% of which were carbohydrate-active enzymes (CAZymes), including a wide diversity of copper-containing oxidoreductases from the auxiliary activities (AA) class (AA1, AA3, AA5, AA7, AA9, AA11-AA13, AA16). Under these specific conditions, while a CRO-glyoxal oxidase from the AA5_1 subfamily was among the most abundantly secreted proteins, the targeted AA5_2 CRO-AlcOx were secreted at lower levels, suggesting heterologous expression as a more promising strategy for CRO-AlcOx production and utilization. C. tabacum and C. destructivum CRO-AlcOx were thus expressed in Pichia pastoris and their preference toward both aromatic and aliphatic primary alcohols was assessed. The CRO-AlcOx from C. destructivum was further investigated in applied settings, revealing a full conversion of C6 and C8 alcohols into their corresponding fragrant aldehydes. IMPORTANCE In the context of the industrial shift toward greener processes, the biocatalytic production of aldehydes is of utmost interest owing to their importance for their use as flavors and fragrances ingredients. CRO-AlcOx have the potential to become platform enzymes for the oxidation of alcohols to aldehydes. However, the secretion of CRO-AlcOx by natural fungal strains has never been explored, while the use of crude fungal secretomes is an appealing approach for industrial application to alleviate various costs pertaining to biocatalysts production. While investigating this primary objective, the secretomics studies revealed unexpected results showing that under the oxidative-stressful conditions we probed, Colletotrichum species can secrete a broad diversity of copper-containing enzymes (laccases, sugar oxidoreductases, LPMOs) usually assigned to “plant-cell wall degradation”, despite the absence of any plant-biomass mimicking compound, and only little amount of CRO-AlcOx were secreted, pointing out at recombinant expression as the most promising path for their biocatalytic application.