Milk oligosaccharide-mediated cross-feeding between and lactobacilli in the gut microbiota of infant rats.

We investigated bacteria that have a nutritional symbiotic relationship with respect to milk oligosaccharides in gut microbiota of suckling rats, with specific reference to sialyllactose (SL) degrading . Our next generation sequencing analysis of the colonic contents of 12-day-old suckling rats revealed that almost half of the bacteria in the microbiota belonged to the Lactobacillaceae family. Major species in the contents were identified as , , and . We then monitored changes in numbers of the above species, , and the bacteria belonging to the family Enterobacteriaceae (i.e., enterobacteria) in the colonic contents of infant rats at 7, 12, 21, 28, and 35 days of age by using real-time PCR assays targeting these bacterial groups. The 7-day-old infant rats had a gut microbiota in which enterobacteria were predominant. Such dominance was replaced by and the concomitant markedly increased in those of 12 and 21 days of ages. During this period, the number of enterobacteria declined dramatically, but that of surged dramatically. Our separate experiment showed that supplementation of culture media with SL promoted the growth of and , with marked production of lactic acid. These findings revealed possible milk oligosaccharide-mediated cross-feeding between and , with the former degrading SL to release lactose to be utilized by the latter.