Metabolic engineering of Mannheimia succiniciproducens for succinic acid production based on elementary mode analysis with clustering.

Mannheimia succiniciproducens, a capnophilic gram-negative rumen bacterium, has been employed for the efficient production of succinic acid. Although M. succiniciproducens metabolism was previously studied using a genome-scale metabolic model, more metabolic characteristics are to be understood. To this end, elementary mode analysis accompanied with clustering ('EMC' analysis) is used to gain further insights on metabolic characteristics of M. succiniciproducens allowing efficient succinic acid production. Elementary modes (EMs) generated from the central carbon metabolic network of M. succiniciproducens are clustered to systematically analyze succinic acid production routes. Based on the results of EMC analysis, zwf gene is identified as a novel overexpression target for the improved succinic acid production. This gene is overexpressed in a previously constructed succinic acid-overproducing M. succiniciproducens LPK7 strain. Heterologous NADPH-dependent mdh is later intuitively selected for overexpression to synergistically improve succinic acid production by utilizing abundant NADPH pool mediated by the overexpressed zwf. The LPK7 strains co-expressing mdh alone and both zwf and mdh genes are subjected to fed-batch fermentation to better examine their succinic acid production performances. Strategies of EMC analysis will be useful for further metabolic engineering of M. succiniciproducens and other microorganisms to improve production of succinic acid and other chemicals of interest.