Ruminal Microbes Exhibit a Robust Circadian Rhythm and Are Sensitive to Melatonin

Abstract

Gut hormones are not only able to regulate digestive, absorptive, and immune mechanisms of the intestine through biological rhythms, but impact the host through their interactions with intestinal microorganisms. Whether hormones in ruminal fluid have an association with the ruminal ecology is unknown. Objectives of the study were to examine relationships between the diurnal change in ruminal hormones and microbiota in lactating cows, and their associations in vivo and in vitro. For the in vivo study, six cows of similar weight (566.8 ± 19.6 kg), parity (3.0 ± 0.0), and milk performance (8,398.7 ± 1,392.9 kg/y) were used. They were adapted to natural light for 2 weeks before sampling and fed twice daily at 07:00 a.m. and 14:00 p.m. Serum, saliva, and ruminal fluid samples were collected at 02:00, 10:00, and 18:00 on the first day and 06:00, 14:00, and 22:00 on the second day of the experimental period. The concentrations of melatonin (MLT), growth hormone (GH), and prolactin (PRL) were measured via radioimmunoassay, whereas amplicon sequencing data were used to analyze relative abundance of microbiota in ruminal fluid. JTK_CYCLE analysis was performed to analyze circadian rhythms of hormone concentrations as well as the relative abundance of microbiota. For the in vitro study, exogenous MLT (9 ng) was added into ruminal fluid incubations to investigate the impacts of MLT on ruminal microbiota. The results not only showed that rumen fluid contains MLT, but the diurnal variation of MLT and the relative abundance of 9% of total rumen bacterial operational taxonomic units (OTUs) follow a circadian rhythm. Although GH and PRL were also detected in ruminal fluid, there was no obvious circadian rhythm in their concentrations. Ruminal MLT was closely associated with Muribaculaceae, Succinivibrionaceae, Veillonellaceae, and Prevotellaceae families in vivo. In vitro, these families were significantly influenced by melatonin treatment, as melatonin treatment increased the relative abundance of families Prevotellaceae, Muribaculaceae while it reduced the relative abundance of Succinivibrionaceae, Veillonellaceae. Collectively, ruminal microbes appear to maintain a circadian rhythm that is associated with the profiles of melatonin. As such, data suggest that secretion of melatonin into the rumen could play a role in host-microbe interactions in ruminants.

Melatonin promotes the growth and development of lambs by increasing growth hormone and testosterone, targeting on apoptosis signaling pathway and intestinal microflora

“…The crosstalk between the microbiota and the tissues of the host will influence the growth and development status of the host (53). It has been showed that melatonin treatment increased the relative abundance of families Prevotellaceae, Muribaculaceae while it reduced the relative abundance of Succinivibrionaceae, Veillonellaceae in ruminal of lactating cows (54). In this study, it was found that melatonin also affected rumen microflora of lambs.…”

Circadian rhythms of hosts and their gut microbiomes: Implications for animal physiology and ecology

“…mice, chickens, and fish; Brooks et al, 2021; Hieke et al, 2019; Parris et al, 2019; Zhang et al, 2021). Other types of microbiomes also undergo diurnal oscillations, including cow rumen microbiomes (Ouyang et al, 2021; Shaani et al, 2018), fish skin microbiomes (Ellison et al, 2021), plant rhizosphere microbiomes (Hubbard et al, 2018), invertebrate microbiomes (Pfenning‐Butterworth et al, 2022; Roeder et al, 2022), and coral microbiomes (Rosenberg et al, 2022), highlighting the ubiquity of diurnal rhythms across host‐associated microbiomes.…”

Melatonin in Health and Disease: A Perspective for Livestock Production

“…Salivary melatonin has roles in regulating inflammatory processes, promoting antioxidant responses, and rapid healing within oral wounds [ 91 ]. Moreover, salivary melatonin concentrations follow a similar circadian rhythm to the pattern in ruminal fluid and ruminal muscularis [ 92 ]. Thus, melatonin secreted into the saliva could be impacting microbial communities throughout the gastrointestinal tract via circadian fluctuations.…”

“…A study within lactating Holstein cows (n = 6) demonstrated a circadian rhythm within the rumen gut microbial populations and found that microbe relative abundance changed with ruminal melatonin concentrations. Specifically, increased melatonin concentrations resulted in increased relative abundance of the families Preovotellaceae and Muribaculaceae; there was a decrease in the relative abundance of the families Succininivibrionaceae and Veillonellaceae [ 92 ]. This is concurrent with previous research demonstrating melatonin’s ability to negatively affect gram-negative bacteria via cytokine production and altered metabolism [ 93 ].…”

“…This is concurrent with previous research demonstrating melatonin’s ability to negatively affect gram-negative bacteria via cytokine production and altered metabolism [ 93 ]. Based on the results, Ouyang et al [ 92 ] hypothesized that the oscillation of melatonin concentrations within the gastrointestinal tract alters key metabolic pathways that impact the dominant phyla (Firmicutes, Proteobacteria, and Bacteroidetes) within the rumen.…”