BackgroundZygosaccharomyces bailii is considered the most problematic acidic food spoilage yeast species due to its exceptional capacity to tolerate high concentrations of weak acids used as fungistatic preservatives at low pH. However, the mechanisms underlying its intrinsic remarkable tolerance to weak acids remain poorly understood. The identification of genes and mechanisms involved in Z. bailii acetic acid tolerance was on the focus of this study. For this, a genomic library from the highly acetic acid tolerant hybrid strain ISA1307, derived from Z. bailii and a closely related species and isolated from a sparkling wine production plant, was screened for acetic acid tolerance genes. This screen was based on the transformation of an acetic acid susceptible Saccharomyces cerevisiae mutant deleted for the gene encoding the acetic acid resistance determinant transcription factor Haa1.ResultsThe expression of 31 different DNA inserts from ISA1307 strain genome was found to significantly increase the host cell tolerance to acetic acid. The in silico analysis of these inserts was facilitated by the recently available genome sequence of this strain. In total, 65 complete or truncated ORFs were identified as putative determinants of acetic acid tolerance and an S. cerevisiae gene homologous to most of them was found. These include genes involved in cellular transport and transport routes, protein fate, protein synthesis, amino acid metabolism and transcription. The role of strong candidates in Z. bailii and S. cerevisiae acetic acid tolerance was confirmed based on homologous and heterologous expression analyses.ConclusionsISA1307 genes homologous to S. cerevisiae genes GYP8, WSC4, PMT1, KTR7, RKR1, TIF3, ILV3 and MSN4 are proposed as strong candidate determinants of acetic acid tolerance. The ORF ZBAI_02295 that contains a functional domain associated to the uncharacterised integral membrane proteins of unknown function of the DUP family is also suggested as a relevant tolerance determinant. The genes ZbMSN4 and ZbTIF3, encoding a putative stress response transcription factor and a putative translation initiation factor, were confirmed as determinants of acetic acid tolerance in both Z. bailii and S. cerevisiae. This study provides valuable indications on the cellular components, pathways and processes to be targeted in order to control food spoilage by the highly acetic acid tolerant Z. bailii and Z. bailii-derived strains. Additionally, this information is essential to guide the improvement of yeast cells robustness against acetic acid if the objective is their use as cell factories.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2278-6) contains supplementary material, which is available to authorized users.

BackgroundThe food spoilage yeast species Zygosaccharomyces bailii exhibits an extraordinary capacity to tolerate weak acids, in particular acetic acid. In Saccharomyces cerevisiae, the transcription factor Haa1 (ScHaa1) is considered the main player in genomic expression reprogramming in response to acetic acid stress, but the role of its homologue in Z. bailii (ZbHaa1) is unknown.ResultsIn this study it is demonstrated that ZbHaa1 is a ScHaa1 functional homologue by rescuing the acetic acid susceptibility phenotype of S. cerevisiae haa1Δ. The disruption of ZbHAA1 in Z. bailii IST302 and the expression of an extra ZbHAA1 copy confirmed ZbHAA1 as a determinant of acetic acid tolerance. ZbHaa1 was found to be required for acetic acid stress-induced transcriptional activation of Z. bailii genes homologous to ScHaa1-target genes. An evolutionary analysis of the Haa1 homologues identified in 28 Saccharomycetaceae species genome sequences, including Z bailii, was carried out using phylogenetic and gene neighbourhood approaches. Consistent with previous studies, this analysis revealed a group containing pre-whole genome duplication species Haa1/Cup2 single orthologues, including ZbHaa1, and two groups containing either Haa1 or Cup2 orthologues from post-whole genome duplication species. S. cerevisiae Cup2 (alias Ace1) is a transcription factor involved in response and tolerance to copper stress. Taken together, these observations led us to hypothesize and demonstrate that ZbHaa1 is also involved in copper-induced transcriptional regulation and copper tolerance.ConclusionsThe transcription factor ZbHaa1 is required for adaptive response and tolerance to both acetic acid and copper stresses. The subfunctionalization of the single ancestral Haa1/Cup2 orthologue that originated Haa1 and Cup2 paralogues after whole genome duplication is proposed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3443-2) contains supplementary material, which is available to authorized users.