The present invention relates to bacterial strains, capable of utilizing glycerol as a carbon source for the fermentative production of succinic acid, wherein said strains are genetically modified so that they comprise a deregulation of their endogenous pyruvate-formate-lyase enzyme activity, as well as to methods of producing organic acids, in particular succinic acid, by making use of such microorganism. The present invention also relates to the downstream processing of the produced organic acids by cation exchange chromatography.