A broad evolutionary perspective of alcoholic fermentation in a non-conventional yeast clade

• Main Author: Lagoas, Catarina Marreiros
• Publication Date: 2021
• Format: Master thesis
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10362/132847
• topic: Horizontal gene transfer; alcoholic fermentation; Wickerhamiella; Starmerella; alcohol dehydrogenase; pyruvate decarboxylase; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

The evolution of alcoholic fermentation in the non-conventional Wickerhamiella/Starmerella (W/S) yeast clade is characterized by the loss of native pyruvate decarboxylase (PDC1) and alcohol dehydrogenase (ADH) genes. In some species, the reacquisition of this via was achieved through horizontal gene transfer (HGT) of ADH and co-option of a native decarboxylase, Aro10. This work aimed to build on the previous knowledge regarding alcoholic fermentation in the W/S clade, by combining in silico data obtained from newly sequenced genomes, with phenotypic assays, aiming to assess alcoholic fermentation abilities and characterization of Adh enzymes, in a subset of species. Three independent HGT events were previously reported to have introduced different bacterial ADH1 in distinct subgroups of the W/S clade. Subgroups A, B and C harbour ADH1a, ADH1b and ADH1c, respectively. Subgroup ADH0 does not carry an ADH1. In this work, data supporting these three HGT events was obtained and two new HGT events of bacterial ADH6 were detected. Most ADH6 genes were acquired in the ancestor of the subgroups reported for ADH1, while one was found in a ADH0 species (Wickerhamiella slavikovae) that seemingly lacks other alcoholic fermentation genes (ADH1, PDC1 and ARO10). As for the remaining species, while ARO10 is present, PDC1 is absent. Ethanol production was generally observed in subgroup A, while its assimilation was verified in subgroups B and C, suggesting that Adh proteins are functional. It was confirmed that Adh1a from Starmerella bombicola is involved in the interconversion of acetaldehyde and ethanol, using NAD(H) and NADP(H) as cofactors, which contrasts with the specificity of Adh proteins from yeasts towards NAD(H). To further understand the evolution of the alcoholic fermentation in the W/S clade, it is essential to combine comparative genomics with the characterization of these enzymes to evaluate their role on the central carbon metabolism.