APPLIED GENETICS AND MOLECULAR BIOTECHNOLOGY HAA1 and PRS3 overexpression boosts yeast tolerance towards acetic acid improving xylose or glucose consumption: unravelling the underlying mechanisms Joana T. Cunha 1 & Carlos E. Costa 1 & Luís Ferraz 1 & Aloia Romaní 1 & Björn Johansson 2 & Isabel Sá-Correia 3 & Lucília Domingues 1 Received: 3 January 2018 /Revised: 12 March 2018 /Accepted: 18 March 2018 /Published online: 2 April 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Acetic acid tolerance and xylose consumption are desirable traits for yeast strains used in industrial biotechnological processes. In this work, overexpression of a weak acid stress transcriptional activator encoded by the gene HAA1 and a phosphoribosyl pyrophosphate synthetase encoded by PRS3 in a recombinant industrial Saccharomyces cerevisiae strain containing a xylose metabolic pathway was evaluated in the presence of acetic acid in xylose- or glucose-containing media. HAA1 or PRS3 overex- pression resulted in superior yeast growth and higher sugar consumption capacities in the presence of 4 g/L acetic acid, and a positive synergistic effect resulted from the simultaneous overexpression of both genes. Overexpressing these genes also im- proved yeast adaptation to a non-detoxified hardwood hydrolysate with a high acetic acid content. Furthermore, the overexpres- sion of HAA1 and/or PRS3 was found to increase the robustness of yeast cell wall when challenged with acetic acid stress, suggesting the involvement of the modulation of the cell wall integrity pathway. This study clearly shows HAA1 and/or, for the first time, PRS3 overexpression to play an important role in the improvement of industrial yeast tolerance towards acetic acid. The results expand the molecular toolbox and add to the current understanding of the mechanisms involved in higher acetic acid tolerance, paving the way for the further development of more efficient industrial processes. Keywords PRS3 and HAA1 overexpression . Acetic acid . Xylose consumption . Industrial Saccharomyces cerevisiae . Cell wall robustness Introduction Over the last years, environmental problems and worldwide economic issues have driven the research interest towards the value of lignocellulosic biomass as a sustainable solution for the production of bioenergy and value-added products (Moyses et al. 2016). Lignocellulosic biomass is a complex structure mainly consisting of lignin, cellulose (composed of glucose monomers) and hemicellulose (containing various hexose and pentose sugars). Pentoses, such as D-xylose, may represent up to 20% of lignocellulose sugar content (Zabed et al. 2016); however, this sugar is not naturally consumed by the yeast Saccharomyces cerevisiae. Furthermore, pretreatment and hy- drolysis stages, required to obtain fermentable sugars from lig- nocellulosic material, may result in the release of toxic com- pounds, such as acetic acid, furfural and hydroxymethylfurfural (HMF). Acetic acid is released mainly from the hemicellulose fraction (Jönsson and Martín 2016) and is a potent inhibitor of microbial growth (Parawira and Tekere 2011). Thus, an eco- nomically viable usage of this biomass requires an efficient utilization of its hemicellulosic fraction, which implies the de- velopment of genetically modified S. cerevisiae strains capable of xylose consumption and with thorough acetic acid tolerance. Joana T. Cunha and Carlos E. Costa contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00253-018-8955-z) contains supplementary material, which is available to authorized users. * Lucília Domingues luciliad@deb.uminho.pt 1 Centre of Biological Engineering (CEB), University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal 2 Center of Molecular and Environmental Biology (CBMA), University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal 3 Institute for Bioengineering and Biosciences, Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal Applied Microbiology and Biotechnology (2018) 102:4589–4600 https://doi.org/10.1007/s00253-018-8955-z