Genomic and proteomic analysis of Tausonia pullulans reveals a key role for a GH15 glucoamylase in starch hydrolysis.

ABSTRACT

Basidiomycetous yeasts remain an almost unexplored source of enzymes with great potential in several industries. Tausonia pullulans (Tremellomycetes) is a psychrotolerant yeast with several extracellular enzymatic activities reported, although the responsible genes are not known. We performed the genomic sequencing, assembly and annotation of T. pullulans strain CRUB 1754 (Perito Moreno glacier, Argentina), a gene survey of carbohydrate-active enzymes (CAZymes), and analyzed its secretome by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) after growth in glucose (GLU) or starch (STA) as main carbon sources. T. pullulans has 7210 predicted genes, 3.6% being CAZymes. When compared to other Tremellomycetes, it contains a high number of CAZy domains, and in particular higher quantities of glucoamylases (GH15), pectinolytic enzymes (GH28) and lignocellulose decay enzymes (GH7). When the secretome of T. pullulans was analyzed experimentally after growth in starch or glucose, 98 proteins were identified. The 60% of total spectral counts belonged to GHs, oxidoreductases and to other CAZymes. A 65 kDa glucoamylase of family GH15 (TpGA1) showed the highest fold change (tenfold increase in starch). This enzyme contains a conserved active site and showed extensive N-glycosylation. This study increases the knowledge on the extracellular hydrolytic enzymes of basidiomycetous yeasts and, in particular, establishes T. pullulans as a potential source of carbohydrate-active enzymes. KEY POINTS • Tausonia pullulans genome harbors a high number of genes coding for CAZymes. • Among CAZy domains/families, the glycoside hydrolases are the most abundant. • Secretome analysis in glucose or starch as main C sources identified 98 proteins. • A 65 kDa GH15 glucoamylase showed the highest fold increase upon culture in starch.