Dietary Lactobacillus delbrueckii Affects Ileal Bacterial Composition and Circadian Rhythms in Pigs

Intestinal bacteria, synchronized with diet and feeding time, exhibit circadian rhythms and anticipate host gut function; however the effect of dietary probiotics on gut bacterial diurnal rhythms remains obscure. In this study, bacteria were sequenced at 6 Zeitgeber times (ZT) from a pig model of ileal T-shaped fistula to test ileal bacterial composition and circadian rhythms after Lactobacillus delbrueckii administration. The results showed that dietary L. delbrueckii enhanced ileal bacterial alpha-diversity at Zeitgeber time (ZT) 16, evidenced by an increased Simpson index compared with control pigs. At the phylum level, Firmicutes was identified as the largest phyla represented in pigs, but dietary L. delbrueckii only increased the abundance of Tenericutes at ZT16. At the genus level, 11/100 genera (i.e., Lactobacillus, Enterococcus, Leptotrichia, Pediococcus, Bifidobacte, Cellulosilyticum, Desulfomicrobium, Sharpea, Eubacterium, Propionivibrio, and Aerococcus) were markedly differentiated in L. delbrueckii-fed pigs and the effect was rhythmicity-dependent. Meanwhile, dietary L. delbrueckii affected six pathways of bacterial functions, such as membrane transport, metabolism of cofactors and vitamins, cell motility, the endocrine system, signaling molecules and interaction, and the nervous system. Cosinor analysis was conducted to test bacterial circadian rhythm in pigs, while no significant circadian rhythm in bacterial alpha-diversity and phyla composition was observed. Lactobacillus, Terrisporobacter, and Weissella exhibited significant rhythmic fluctuation in the control pigs, which was disturbed by probiotic exposure. In addition, dietary L. delbrueckii affected circadian rhythms in ileal Romboutsia, Erysipelatoclostridium, Cellulosilyticum, and Eubacterium abundances. Dietary L. delbrueckii affected both ileal bacterial composition and circadian rhythms, which might further regulate gut function and host metabolism in pigs.