A gut bacterium that builds muscle strength
Sarcopenia is often framed as a failure of exercise and nutrition. A new study now links one gut bacterium, Roseburia inulinivorans, to muscle strength in humans and shows a causal effect in micevia amino acid shifts.
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The gut microbiota regulates host metabolism, inflammation, and tissue function, yet its role in muscle health has remained a blind spot. While the concept of a gut-muscle axis has gained traction, no specific bacterial species had been causally linked to muscle strength.
A new study 1 published in Gut by Martinez-Tellez et al. from the Leiden University Medical Center and the University of Granada set out to fill that gap.
Gut-muscle axis
A bidirectional communication pathway through which gut microbes, their metabolites, and immune signals influence muscle mass and function. This study provides direct evidence that a single bacterial species within this axis can causally modulate muscle strength. 1
Sarcopenia
The progressive, age-related loss of skeletal muscle mass, strength, and function, contributing to frailty and poor clinical outcomes. The observed decline of R. inulinivorans with age suggests a potential microbiome-based therapeutic avenue for this condition. 1
From human association to causal proof in mice
The team conducted metagenomic analyses in two human cohorts:
- 90 young adults (18–25 years)
- and 33 older adults (65–75 years), extensively phenotyped for muscle strength.
Among all bacterial taxa, the relative abundance of Roseburia inulinivorans, but not other Roseburia species, was positively associated with handgrip strength in both age groups. Older adults with detectable R. inulinivorans exhibited 29% higher handgrip strength (p<0.01). In young adults, higher abundance also correlated with leg press and bench press performance (r≥0.26, p<0.05).
Roseburia inulinivorans
A butyrate-producing anaerobic bacterium of the Lachnospiraceae family, identified here as the only Roseburia species specifically and causally linked to enhanced muscle strength in both human cohorts and a murine model. 1
To test causality, 32 antibiotic-treated mice received oral gavage of :
- R. inulinivorans,
- R. faecis,
- R. intestinalis, or vehicle three times weekly for eight weeks.
Only R. inulinivorans induced a remarkable ~30% increase in forelimb grip strength (p<0.001). Muscle fibre analysis confirmed increased cross-sectional area, a higher frequency of large fibres (>5000 µm²), and a shift from type I to type II fibres, the fast-twitch fibres critical for force generation.
Type II muscle fibres
Fast-twitch skeletal muscle fibres characterised by high glycolytic capacity and rapid force generation. R. inulinivorans supplementation shifted fibre composition toward type II, coinciding with increased muscle fibre size and grip strength in mice. 1
An unexpected mechanism: amino acids, not butyrate
As Roseburia species are established butyrate producers, short-chain fatty acids were the expected driver. Yet caecal SCFA levels remained unchanged.
The key metabolic signature of R. inulinivorans lay elsewhere: a marked decrease in caecal amino acids including :
- methionine,
- leucine,
- isoleucine,
- valine,
- alanine,
- and lysine.
Genomic data indicate that R. inulinivorans depends on a unique succinylation-dependent lysine biosynthesis pathway and cannot use urea as a nitrogen source, likely increasing its luminal amino acid uptake. Downstream, untargeted metabolomics in skeletal muscle revealed activation of the purine and pentose phosphate pathways, central routes for nucleotide biosynthesis, NADPH production, and redox balance.
Purine metabolism can be stimulated by mTORC1, a master regulator of anabolic signalling and muscle growth, suggesting a mechanistic link between microbial amino acid consumption in the gut and muscle fibre hypertrophy.
29%
Among older adults, the detectable presence of R. inulinivorans is associated with a 29% increase in grip strength. ¹
A probiotic candidate for aging muscles
R. inulinivorans abundance was significantly lower in older versus young adults, a trend confirmed across 3,512 publicly available metagenomes (p=0.016).
The Roseburia genus is also depleted in:
- sarcopenia,
- cerebral palsy,
- anorexia nervosa,
- and cancer-related cachexia.
Sarcopenia: gut microbiota involved in the loss of skeletal muscle mass and function?
Notably, strength training has been shown to selectively increase Roseburia abundance, hinting at a bidirectional gut-muscle dialogue.
Taken together, these findings position R. inulinivorans as a species-specific modulator of the gut-muscle axis and a compelling probiotic candidate for nutraceutical strategies against age-related muscle wasting, though rigorous human intervention trials remain the critical next step.
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