Engineering class-B vitamin biosynthesis in Saccharomyces cerevisiae (IMX2816)
Saccharomyces cerevisiae is bradytroph for class B vitamins, it means that yeast cells exhibit slower growth in the absence of an external source of these metabolites. Alleviating these nutritional requirements for optimal growth performance would represent a valuable phenotypic characteristic for industrial strains since this would result in cheaper processes that would also be less susceptible to contaminations. In the present study, suboptimal growth of S. cerevisiae in absence of either pantothenic acid, para-aminobenzoic acid (pABA), pyridoxine, inositol and biotin were corrected by single or double gene overexpression of ScFMS1, ScABZ1 and ScABZ2, ScSNZ1 and ScSNO1, ScINO1 and the Cyberlindnera fabianii BIO1, respectively. Several strategies were attempted to improve growth of S. cerevisiae CEN.PK113-7D in absence of thiamine, revealing that overexpression of ScTHI4 and ScTHI4 - ScTHI5 improved growth up to 83% of the maximum specific growth rate of the reference CEN.PK113-7D in vitamins containing medium.By combining overexpression of solely seven S. cerevisiae genes and the heterologous CfBIO1, the strain IMX2816 was fast-growing at a maximum specific growth rate of 0.33 h-1 in medium devoid of all vitamins. Secondly, this strain exhibited physiological performances in oxic glucose-limited chemostat cultures at a dilution rate of 0.1 h-1 in absence of vitamins similar to that of the reference strain CEN.PK113-7D grown in fully supplemented medium. These physiological similarities were further emphasized by the limited differences observed in comparative transcriptome analysis from the chemostat culture grown cells that were essentially affecting genes of the class B vitamins biosynthetic pathways. This work paves the way towards construction of the first fast growing vitamin-independent S. cerevisiae strain.