Lactobacilli biology, applications and host interactions

Lactobacilli encompass more than 300 species, spanning 25 genera, found in the microbiomes of humans, animals and plants with relevance in agriculture, foods and medicine. Lactobacilli comprise all bacteria previously assigned to the Lactobacillus genus and, similar to other lactic acid bacteria, are characterized by their saccharolytic, fermentation-energy metabolism and diverse enzymatic pathways that support redox balance and maintain intracellular pH. Some lactobacilli are pervasive in dairy, meat and plant foods, where they either contribute to spoilage and food waste or are desired and necessary for the production of fermented foods and animal feed. Strains of lactobacilli are the most applied probiotics tested in clinical studies. The study of host-associated intestinal and vaginal microbiomes has demonstrated that lactobacilli drive epithelial and immune cell responses, resulting in mainly beneficial effects on host health. This Review explores both established and emerging concepts related to this group of microorganisms. It highlights central tenants of their genetic diversity, metabolism, stress tolerance and distribution across host-associated microbiomes, as well as their importance in fermented foods and in health modulation as probiotics. With this accumulated knowledge, there remain substantial opportunities for expanded application of lactobacilli across different domains relevant to food production and health.