Carbohydrate stress-related response in Bifidobacterium pseudolongum subsp globosum

Bifidobacteria are indigenous components of human and animal gastrointestinal microbiota, and their health-promoting benefits have long been recognized. Of the 36 currently described species of the Bifidobacterium genus, 8 contain plasmids, most of which are cryptic. It is possible that plasmid presence is related very closely to environmental change, so in conditions of stress this presence could be specifically controlled. For plasmid-positive Bifidobacterium pseudolongum subsp. globosum RU809/1, the influence of the type and concentration of the carbohydrate source is evident in the dramatic pVS809 curing effect when growth is conducted in the presence of 0.15% (w/v) glucose, lactose, maltose, melibiose, raffinose or starch. The effect is linked to carbohydrate starvation, not to carbohydrate abundance, and is independent of biomass growth. Plasmid curing was achieved after one or two consecutive transfers, also in cells grown on medium containing 0.15% arabinose, fructose, galactose and sucrose, but not mannose, ribose or xylose. Knowing plasmid behavior in stressful conditions, like carbon source availability, has allowed an early insight into carbohydrate starvation as a curing agent for bifidobacteria. Furthermore, knowledge of plasmid behavior in stressful conditions could be important not only in genetics and ecology but also in food-grade and pharmaceutical applications for the development of cloning and expression vector systems for bifidobacteria.