title: Microbial shifts in the aging mouse gut.
abstract: BACKGROUND
  The changes that occur in the microbiome of aging individuals are unclear, especially in light of the imperfect correlation of frailty with age. Studies in older human subjects have reported subtle effects, but these results may be confounded by other variables that often change with age such as diet and place of residence. To test these associations in a more controlled model system, we examined the relationship between age, frailty, and the gut microbiome of female C57BL/6 J mice.
  
  
  RESULTS
  The frailty index, which is based on the evaluation of 31 clinical signs of deterioration in mice, showed a near-perfect correlation with age. We observed a statistically significant relationship between age and the taxonomic composition of the corresponding microbiome. Consistent with previous human studies, the Rikenellaceae family, which includes the Alistipes genus, was the most significantly overrepresented taxon within middle-aged and older mice. The functional profile of the mouse gut microbiome also varied with host age and frailty. Bacterial-encoded functions that were underrepresented in older mice included cobalamin (B12) and biotin (B7) biosynthesis, and bacterial SOS genes associated with DNA repair. Conversely, creatine degradation, associated with muscle wasting, was overrepresented within the gut microbiomes of the older mice, as were bacterial-encoded β-glucuronidases, which can influence drug-induced epithelial cell toxicity. Older mice also showed an overabundance of monosaccharide utilization genes relative to di-, oligo-, and polysaccharide utilization genes, which may have a substantial impact on gut homeostasis.
  
  
  CONCLUSIONS
  We have identified taxonomic and functional patterns that correlate with age and frailty in the mouse microbiome. Differences in functions related to host nutrition and drug pharmacology vary in an age-dependent manner, suggesting that the availability and timing of essential functions may differ significantly with age and frailty. Future work with larger cohorts of mice will aim to separate the effects of age and frailty, and other factors.
authors.affiliation: Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia Canada ; Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Morgan Gi
authors.initials: MG
authors.lastname: Langille
authors.affiliation: Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia Canada ; Mycobacteriology Unit, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Conor J
authors.initials: CJ
authors.lastname: Meehan
authors.affiliation: Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Jeremy E
authors.initials: JE
authors.lastname: Koenig
authors.affiliation: Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Akhilesh S
authors.initials: AS
authors.lastname: Dhanani
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Rose
authors.affiliation: Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia Canada ; Department of Medicine (Geriatric Medicine), Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Howlett
authors.affiliation: Faculty of Computer Science, Dalhousie University, Halifax, Nova Scotia Canada.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Beiko
keywords: Aging; Alistipes; B12; Frailty index; Mice; Microbiome