Phylogenomic Relationships between Amylolytic Enzymes from 85 Strains of Fungi

Fungal amylolytic enzymes, including alpha-amylase, gluocoamylase and alpha-glucosidase, have been extensively exploited in diverse industrial applications such as high fructose syrup production, paper making, food processing and ethanol production. In this paper, amylolytic genes of 85 strains of fungi from the phyla Ascomycota, Basidiomycota, Chytridiomycota and Zygomycota were annotated on the genomic scale according to the classification of glycoside hydrolase (GH) from the Carbohydrate-Active enZymes (CAZy) Database. Comparisons of gene abundance in the fungi suggested that the repertoire of amylolytic genes adapted to their respective lifestyles. Amylolytic enzymes in family GH13 were divided into four distinct clades identified as heterologous alpha-amylases, eukaryotic alpha-amylases, bacterial and fungal alpha-amylases and GH13 alpha-glucosidases. Family GH15 had two branches, one for gluocoamylases, and the other with currently unknown function. GH31 alpha-glucosidases showed diverse branches consisting of neutral alpha-glucosidases, lysosomal acid alpha-glucosidases and a new clade phylogenetically related to the bacterial counterparts. Distribution of starch-binding domains in above fungal amylolytic enzymes was related to the enzyme source and phylogeny. Finally, likely scenarios for the evolution of amylolytic enzymes in fungi based on phylogenetic analyses were proposed. Our results provide new insights into evolutionary relationships among subgroups of fungal amylolytic enzymes and fungal evolutionary adaptation to ecological conditions.