Transcriptomic analysis reveals 3 important carbohydrate-active enzymes contributing to starch degradation of the oleaginous yeast <i>Lipomyces starkeyi</i>

The oleaginous yeast Lipomyces starkeyi has a high capacity for starch assimilation, but the genes involved and specific mechanisms in starch degradation remain unclear. This study aimed to identify the critical carbohydrate-active enzyme (CAZyme) genes contributing to starch degradation in L. starkeyi. Comparative transcriptome analysis of cells cultured in glucose and soluble starch medium revealed that 55 CAZymes (including transcript IDs 3772, 1803, and 7314) were highly expressed in soluble starch medium. Protein domain structure and disruption mutant analyses revealed that 3772 encodes the sole secreted α-amylase (LsAmy1p), whereas 1803 and 7314 encode secreted α-glucosidase (LsAgd1p and LsAgd2p, respectively). Triple-gene disruption exhibited severely impaired growth in soluble starch, dextrin, and raw starch media, highlighting their critical role in degrading polysaccharides composed of glucose linked by α-1,4-glucosidic bonds. This study provided insights into the complex starch degradation mechanism in L. starkeyi.