Microbial colonies capable of fermenting L-malic acid to L-lactic acid were identified by means of a dark blue halo which formed after the colonies had been grown on medium containing malic acid and then covered with a soft agar overlay containing L-lactic acid dehydrogenase, nicotinamide adenine dinucleotide, phenazine methosulfate, and nitro blue tetrazolium. The system is stereospecific and discriminates between the production of D-lactic and L-lactic acid. Chromatographic analysis of the medium adjacent to the colony distinguishes between those colonies producing L-lactate from L-malate and those producing DL-lactate from glucose. The system may be used to identify wine microbes capable of performing a malo-lactic fermentation, comparing two bacterial strains for their ability to perform a malo-lactic fermentation, and for the identification of clones of an organism carrying a recombinant DNA vector with the genetic material necessary for malo-lactic fermentation.
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Subden et al. (1982) studied this question.