From field to fermentation: The origins of Lactococcus lactis and its domestication to the dairy environment

• Lactococcus lactis inhabits in a wide range of environmental niches.
• Due to phenotype–genotype mismatching, a complex taxonomical structure exists.
• Adaptation to the milk environment has led to significant changes in the L. lactis genome.
• Non-dairy lactococci may have beneficial applications in dairy fermentations.
• Strains from non-dairy environments should be evaluated for safety for use in foods.

Lactococcus lactis is an organism of substantial economic importance, used extensively in the production of fermented foods and widely held to have evolved from plant strains. The domestication of this organism to the milk environment is associated with genome reduction and gene decay, and the acquisition of specific genes involved in protein and lactose utilisation by horizontal gene transfer. In recent years, numerous studies have focused on uncovering the physiology and molecular biology of lactococcal strains from the wider environment for exploitation in the dairy industry. This in turn has facilitated comparative genome analysis of lactococci from different environments and provided insight into the natural phenotypic and genetic diversity of L. lactis. This diversity may be exploited in dairy fermentations to develop products with improved quality and sensory attributes. In this review, we discuss the classification of L. lactis and the problems that arise with phenotype/genotype designation. We also discuss the adaptation of non-dairy lactococci to milk, the traits associated with this adaptation and the potential application of non-dairy lactococci to dairy fermentations.