Manipulating the growth environment through co-culture to enhance stress tolerance and viability of probiotic strains in the gastrointestinal tract

ABSTRACT The viability of probiotics in the gastrointestinal tract is essential because it has an important role in their health benefits. Plasticity is a phenomenon associated with stress tolerance in bacteria, and stress tolerance of probiotic strains can be induced by the use of additives and weak stress. However, some of these processes are difficult to implement in the manufacture of probiotic beverages, and there are few methods that can be easily applied. Co-culture techniques have been used to produce fermented beverages and may impart distinct characteristics through differences in the culture environment compared with those of monoculture. Here, we show that the stress tolerance of a probiotic strain was altered by co-culture with other strains already used in product manufacturing. Stress tolerance in Lacticaseibacillus paracasei strain Shirota was enhanced by co-culture with Lactococcus lactis subsp. lactis YIT 2027 as a result of an earlier pH decrease. Therefore, the stress tolerance was similarly improved in monocultures where pH was manipulated. Strains with improved stress tolerance had an increase in dihydrosterculic acid in the cell membrane, with altered gene transcription in energy metabolism, lipid metabolism, and chaperone genes. Moreover, fermented beverage consumption studies revealed that the probiotics produced through co-culture were significantly more viable in the human gastrointestinal tract than those produced through monoculture. These data suggested that co-culture with specific strains can significantly enhance the viability of probiotic strains in the human gastrointestinal tract. IMPORTANCE The viability of probiotics in the human gastrointestinal tract is important, as some reports indicate that the health benefits of live bacteria are greater than those of dead ones. Therefore, the higher the viability of the probiotic strain, the better it may be. However, probiotic strains lose their viability due to gastrointestinal stress such as gastric acid and bile. This study provides an example of the use of co-culture or pH-controlled monoculture, which uses more stringent conditions (lower pH) than normal monoculture to produce probiotic strains that are more resistant to gastrointestinal stress. In addition, co-cultured beverages showed higher viability of the probiotic strain in the human gastrointestinal tract than monocultured beverages in our human study. The viability of probiotics in the human gastrointestinal tract is important, as some reports indicate that the health benefits of live bacteria are greater than those of dead ones. Therefore, the higher the viability of the probiotic strain, the better it may be. However, probiotic strains lose their viability due to gastrointestinal stress such as gastric acid and bile. This study provides an example of the use of co-culture or pH-controlled monoculture, which uses more stringent conditions (lower pH) than normal monoculture to produce probiotic strains that are more resistant to gastrointestinal stress. In addition, co-cultured beverages showed higher viability of the probiotic strain in the human gastrointestinal tract than monocultured beverages in our human study.