Eating habits in industrialised societies are far removed from those of ancient humans. This is impacting our intestinal flora, as newly discovered cellulose-degrading bacteria are being lost from the human gut microbiome, especially in industrial societies. The study, published in Science, reveals that the eating habits in industrialised societies are impacting our intestinal flora, as newly discovered cellulose-degrading bacteria are being lost from the human gut microbiome, especially in industrial societies.
Lead investigator Sarah Moraïs from Ben-Gurion University (BGU) explains that fiber has always been a mainstay of the human diet throughout human evolution and is a main component in the diet of our primate ancestors. Fiber keeps our intestinal flora healthy. Moraïs and her team identified important new members of the human gut microbiome, cellulose-degrading bacteria named Ruminococcus. These bacteria degrade cellulose by producing large and highly specialized extracellular protein complexes called cellulosomes.
Everyone knows that fiber is healthy and an important part of our daily diet. But what is fiber and why is it healthy? Fiber is cellulose, the stringy stuff that plants are made of leaves, stems, roots, stalks, and tree-trunks (wood) are made of cellulose. The purest form of cellulose is the long, white fibers of cotton. Dietary fiber comes from vegetables or whole grain products. Fiber helps to keep our intestinal flora (scientists call it our gut microbiome) happy and balanced. Fiber serves as the starting point of a natural food chain. It begins with bacteria that can digest cellulose, providing the rest of our microbiome with a balanced diet.
Cellulosomes are engineered by bacteria to attach to cellulose fibers and peel them apart, like the individual threads in a piece of rope. The cellulosomal enzymes then break down the individual threads of fiber into shorter chains, which become soluble. They can be digested, not only by Ruminococcus, but also by many other members of the gut microbiome. The production of cellulosomes puts Ruminococcus at the top of the fiber-degradation cascade that feeds a healthy gut microbiome. However, the study reveals that these cellulosome-producing bacteria are being lost from the human gut microbiome, especially in industrialized societies.
The study also indicates that Western culture is taking its toll on our microbiome. Sampling of human cohorts revealed that Ruminococcus strains are indeed robust components of the human gut microbiome among human hunter-gatherer societies and among rural human societies, but that they are sparse or missing in human samples from industrialized societies.
The evolutionary history of Ruminococcus is complicated, and it looks like humans have acquired important components of a healthy gut microbiome from livestock that they domesticated early in human evolution. Prof. Mizrahi from BGU, senior author of the study, explains that the cellulosome-producing bacteria of humans seem to have switched hosts during evolution, as the strains from humans are more closely related to the strains from livestock than to the strains from our own primate ancestors.