Enhancing the production of uridine 5′-monophosphate by recombinant Saccharomyces cerevisiae using a whole cell biocatalytic process

Attempts were made with success to produce uridine 5′-monophosphate (UMP) from orotic acid by a recombinant Saccharomyces cerevisiae strain pYX212-URA5/BJX12, using the whole cell biocatalytic process. URA5 and URA3 genes, encoding orotate phosphoribosytransferase (OPRTase) and orotidine monophosphate decarboxylase (ODCase), respectively were successfully overexpressed in the industrial yeast strain. As a result, S. cerevisae pYX212-URA5/BJX12 exhibited the highest biocatalytic ability, in contrast with the original industrial yeast strain and S. cerevisae pYX212/BJX12 that overexpressed ODCase only. It indicated that the first step of UMP production from orotic acid is a rate-limiting step. Effects of cultivation for the recombinant strain and biocatalytic reaction conditions on UMP production were also investigated. Cultivating the cells in malt extract medium for 36 h in the exponential phase of growth is in favor of converting orotic acid to UMP. To acquire a higher UMP yield, the conditions of the whole cell biocatalytic reaction were optimized and up to 3.8 g l^-1 UMP was produced in 24 h consequently. The yield was fivefold higher than the original UMP yield from the industrial yeast. In addition, the accumulation of 2.6 g l^-1 UDP (uridne 5′-diphosphate) in the process demonstrated the possibility for further genetic manipulation: deleting the UMPK (Uridylate Kinase, catalyzing UMP-UDP).