Cryptic diversity of cellulose-degrading gut bacteria in industrialized humans

Abstract

Humans, like all mammals, depend on the gut microbiome for digestion of cellulose, the main component of plant fiber. However, evidence for cellulose fermentation in the human gut is scarce. We have identified ruminococcal species in the gut microbiota of human populations that assemble functional multienzymatic cellulosome structures capable of degrading plant cell wall polysaccharides. One of these species, which is strongly associated with humans, likely originated in the ruminant gut and was subsequently transferred to the human gut, potentially during domestication where it underwent diversification and diet-related adaptation through the acquisition of genes from other gut microbes. Collectively, these species are abundant and widespread among ancient humans, hunter-gatherers, and rural populations but are rare in populations from industrialized societies thus indicating potential disappearance in response to the westernized lifestyle.

Dietary fibre optimisation in support of global health

“…Based on modern hunter‐gatherer societies, daily dietary fibre intakes may have been in the order of 70–130 g, much higher than the current targets of around 20–40 g in industrialised societies (Tannock, 2024 ). A study targeted at cellulose‐degrading ruminococci revealed that they are more prevalent and abundant in humans in non‐industrialised societies, in agreement with their consumption of cellulose‐rich diets (Moraïs et al., 2024 , Table 1 ). Higher abundance of Treponema species has also been found in traditional societies, a genus known to harbour pathogenic species (for example T. pallidum , T. denticola ).…”

A 28-Day Repeated Oral Administration Study of Mechanically Fibrillated Cellulose Nanofibers According to OECD TG407

“…It is possible that the effect of fib-CNF on intestinal bacteria led to weight loss. Numerous studies and review articles discuss the degradation of cellulose and other dietary fibers by intestinal bacteria [24][25][26][27][28][29][30][31][32][33][34]. Although cellulose is a central component of plant fiber and is abundant in diets with plant-derived foods, humans, like other mammals, rely on gut microbiota to break down cellulose.…”