Evolutionary changes of an intestinalLactobacillus reuteriduring probiotic manufacture

ABSTRACT Probiotic bacteria are frequently used to treat intestinal (and other types of diseases) or to improve health, however little is known about the evolutionary changes of these bacteria during probiotic manufacture. It has been observed that when bacteria adapt to a new environment, they lose the skills to thrive in the original niche. In this study, a strain of Lactobacillus reuteri was isolated from the duodenum of a mouse and subjected to 150 serial passes in milk to simulate industrial propagation of probiotic bacteria. The strain adapted to milk outperformed its ancestor in milk, but it showed reduced aptitude to grow culture media, and possibly in mouse intestines. Bacterial adaptation to milk seemed to select a number of non-synonymous mutations in metabolic genes. IMPORTANCE Bacteria in the microbiota must endure hostile conditions including antagonism from other members of the microbial community. Little is known about the evolution of probiotic bacteria in the dairy industry. We show that repeated growth of L. reuteri in milk results in reduced ability to grow in culture medium and possibly colonize the mammalian intestine. Our results contribute to the notion that probiotic bacteria colonize only transiently intestines.