Strategy for yeast improvement

Selection and genetic improvement of yeast starter cultures are based on the ability to achieve a specific task or to perform a precise function. The process can be summarized into few steps: i) the knowledge of yeast microbiota in a specific ecological niche to yield species suitable to grow on specific substrates; ii) clonal selection for obtaining a wide genetic background; iii) definition of desired traits for yeast selection. However the selection of wild strains having complete combination of all traits is not so easy to obtain. There are many strategies for improving yeasts and increasing the recombination of all desired traits within an unique genome. The choice of most suitable strategy is mainly based on three factors: the genetic nature of traits (monogenic or polygenic), the knowledge of the genes involved, the aim of the genetic manipulation.Recent developments in genetic dissection of yeast quantitative traits highlighted how the several interesting traits can be complex and influenced by several genes. In a context of low phenotype-genotype correlation, both the rational approach involving DNA recombinant technologies and the traditional random techniques based on mutagenesis meet serious obstacles. Otherwise, different blind strategies, involving the cell entire genome, can be applied in order to obtain quickly strains with interesting recombinant traits. Laboratory sexual hybridization and genome shuffling are accelerated evolutionary approaches that allow to obtain desired complex phenotypes more rapidly than any normal rational methods.