Functional Analyses of the Malolactic Wine Yeast ML01

Abstract

Deacidification of grape musts and wines is important for the production of well-balanced wines. The bacterial malolactic fermentation (MLF) process is unreliable and stuck MLF often leads to spoilage of wines and the production of biogenic amines. The genetically engineered wine yeast, ML01, is a Prise de Mousse strain that contains the malate transport gene (<i>mae1</i>) from <i>Schizosaccharomyces pombe</i> and the malolactic gene (<i>mleA</i>) from <i>Oenococcus oeni</i>, stably integrated into the genome at the <i>URA3</i> locus. Both genes were isolated from wine-related microorganisms and are expressed under control of the <i>Saccharomyces cerevisiae PGK1</i> promoter and terminator sequences. ML01 is capable of decarboxylating up to 9.2 g/L of malate to equimolar amounts of lactate in Chardonnay grape must during the alcoholic fermentation. ML01 contains no antibiotic resistance marker genes or vector DNA sequences. The presence of the malolactic cassette in the genome does not affect growth, ethanol production, fermentation kinetics, or metabolism of ML01. Wines produced by the ML01 yeast have lower volatile acidity and improved color properties than wines produced with the parental yeast and a bacterial MLF. Analysis of the volatile compounds, sensory analyses, and industrial production of wine indicate that ML01 is suitable for the commercial production of quality wine.