Lactobacillus genus (overview)

The lactic acid bacteria — referred to collectively as 'LAB' or as the Lactobacillus genus in older taxonomy — are the most consequential microbial family in fermented foods. They drive the souring, preservation, and flavor development in lacto-fermented vegetables, dairy products, sourdough breads, fermented meats, kvass, kombucha (alongside yeast), and many fermented condiments. Without LAB activity, much of the world's fermentation heritage would not exist in recognizable form.

In 2020, taxonomists at the International Committee on Systematic Bacteriology reclassified the historically unwieldy Lactobacillus genus into 25 separate genera based on genomic phylogeny. L. plantarum became Lactiplantibacillus plantarum; L. brevis became Levilactobacillus brevis; many others moved. The new genera better reflect evolutionary relationships, but the umbrella term 'Lactobacillus' remains in common food-science usage and most home-fermentation literature.

Functionally, LAB are categorized as *homofermentative (producing lactic acid almost exclusively from sugars — L. plantarum, L. acidophilus, L. delbrueckii) or heterofermentative (producing lactic acid plus CO₂, acetic acid, and ethanol — Leuconostoc, L. brevis, L. fermentum*). The split matters: heterofermenters drive the early phase of many lacto-vegetable ferments because their CO₂ production displaces air and acidifies enough to suppress competitors; homofermenters dominate the final phase because they are more acid-tolerant.

Most LAB are microaerophilic (preferring low-oxygen environments), tolerate pH down to 3.5 or below, and grow optimally between 20-40°C depending on species. The food-relevant LAB are non-pathogenic and most carry GRAS (Generally Recognized As Safe) status from regulatory agencies. The probiotic claims associated with many LAB are real for some species and overstated for others; the encyclopedia presents specific claims at the species level.

LAB's metabolic core is lactic acid fermentation: glucose → 2 lactate via the Embden-Meyerhof-Parnas pathway (homofermenters) or glucose → lactate + CO₂ + ethanol via the phosphoketolase pathway (heterofermenters). The acid acidifies the substrate, which preserves the food and selects against spoilage organisms while contributing the tangy, sour flavor that defines the LAB-fermented food category.