Core strategies of lactic acid biosynthesis in key Lactobacillaceae species: Phylogenetic patterns, metabolic pathways, and genetic regulation

Lactic acid bacteria of the Lactobacillaceae family play a key role in the food, chemical, agricultural, cosmetic and pharmaceutical industries as the main producer of lactic acid. The main success in production of lactic acid is achieved due to introduction of genetic engineering methods and precision fermentation aimed at the control of synthesis of individual optically clean L/D-isomers and utilization of certain components of sugar-containing substrates of nutrient media. At the same time, bacteria Lactobacillaceae have several natural evolutionary advantages that ensure success of their industrial use, including high acid resistance, productivity and safety. Lactobacillus delbrueckii, L. amylovorus, L. acidophilus, Lacticaseibacillus сasei, L. paracasei , Lactiplantibacillus plantarum and some others can be mentioned as the most promising strains — producers of lactic acid in natural conditions. Productivity of strains to a large extend depends on their ability to ferment specific substrates, first of all, different carbohydrate sources. The use of wastes of the food, agricultural and timber industries as substrates for largescale production of lactic acid is of particular scientific and practical interest. This approach makes it possible to significantly reduce expenses on complex nutrient media and cut production costs. The understanding of the main strategies of substrate utilization by various representatives of Lactobacillaceae allows for a more specific choice of a strain. In this review, the main attention is given to the key peculiarities of fermentation of L. с asei , L. delbrueckii, L. plantarum, and L. acidophilus strains with account for their phylogenetic characteristics and metabolic features. The paper examines the central mechanisms of the utilization of carbohydrates, substrate-specific activation of alternative pathways of metabolism, as well as key genes and their patterns associated with lactic acid synthesis. The authors describe the Embden–Meyerhof–Parnas metabolic pathway, pentose phosphate and phosphoketolase pathways, mechanism of carbon catabolite repression and the role of the Leloir pathway. The role of the key enzymes participating in the process of substrate utilization and formation of lactic acid, including lactate dehydrogenase, lactate racemase, aldolase, citrate lyase and others, is demonstrated.