A genomic view on lactic metabolism

Lactic acid bacteria relate in many ways to the well-being and the economic activity of humans. Lactic acid bacteria are recognised as human pathogens but also are beneficial members of commensal microbial communities in humans and animals, and are used as probiotics. Lactic acid bacteria impact food quality and safety both as beneficial fermentation microbes and as spoilage organisms. Owing to their multi-faceted relationship to humans, the carbohydrate metabolism of lactic acid bacteria has been subject to research for more than a century. The aim of this review is to link the wealth of knowledge on lactic metabolism to the currently available genomic information on lactic acid bacteria. Homofermentative and heterofermentative lactic acid bacteria take a substantially different approach to energy generation, have different substrate preferences and thus co-exist in multiple ecological niches. Many lactic acid bacteria maintain electron transfer chains to use oxygen, nitrate or iron as terminal electron acceptors under suitable conditions. The metabolism of organic acids and diols contributes to acid resistance and support stationary-phase survival. The ecology of lactic acid bacteria also shapes metabolic preferences and several metabolic traits differentiate insect associated, vertebrate-host adapted, free living and domesticated lactic acid bacteria. Knowledge of metabolic preferences that relate to phylogeny or the adaptation to different ecological niches facilitates selection of starter cultures for conventional and novel food fermentations.