Mining the diversity of plant-associated lactic acid bacteria

Lactic acid bacteria (LAB) are ubiquitous in food production and processing environments. These bacteria are best known for their fermentative metabolism converting mono/di-saccharides to organic acids, resulting in increased acidity and altered organoleptic qualities of foods and beverages. Aside from this common property, LAB constitute a very diverse collection of bacteria encompassing numerous species (such as Lactobacillus, Leuconostoc, and Weissella) and unlimited numbers of strains with extensive genotypic and phenotypic differences that are currently only partly understood. We are investigating the LAB associated with plants (leaves and fruits). Our studies are focused on the diversity of plant-associated LAB and the unique adaptations of those strains that support growth on plant tissues. Our investigations of a collection of 84 LAB strains from 29 species and 24 distinct fresh/fermented plant sources has uncovered a breadth of phenotypes. These differences include carbon source preferences (hexoses, pentoses, and oligosaccharides), the capacity for biofilm formation, and tolerance to a variety of environmental stresses (low and high temperatures, oxidative stress, low pH, and salinity). Phenotypic diversity was particularly notable for strains of Lactobacillus plantarum. These results combined with comparative genomic analyses are providing new knowledge on the novel capacities of LAB that can be exploited in new or improved food fermentations or leveraged to reduce their prevalence as spoilage agents that impair product shelf-life and quality.