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Selfishness in human gut – some bacteria just do not share food

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Posted October 23, 2019

Selfishness sounds like a terrible quality to have, but in nature it’s just one of the survival mechanisms. You have to take care of yourself and your offspring before thinking about helping others. But what is surprising is that scientists from the Quadram Institute in Norwich and the University of York found human gut bacteria Ruminococcus gnavus to be selfish as well.

Ruminococcus gnavus struggle to colonize gut mucus, if selfish genes are removed. Image by Laura Vaux, the Quadram Institute

Ruminococcus gnavus is one of millions of microbes living in human gut. It feeds on acidic sugars (called sialic acid) found in the protective mucus that lines the gut. Scientists found that R. gnavus gains advantage against other microbes by keeping the most important nutrients to itself. This may sound ordinary for you, but other mucus-foraging bacteria release a type of food called sialic acid for other members of the microbiota to metabolise. Meanwhile R. gnavus modifies it so that it can be the only one to benefit from it.

The mechanism of this selfishness is actually quite interesting. R. gnavus releases modified sialic acid, which is then carried to its cells by specialized proteins. Once acid is inside, modification can be removed and sugary acids can be metabolised as a source of nutrition. Scientists removed genes responsible for this mechanism and found that at that point R. gnavus started struggling to colonise the mucus layer in the gut. This shows that the strategy of selfishness is very important for R. gnavus and without it this bacterium would struggle to survive.

Professor Nathalie Juge, lead author of the study, said: “We think that by modifying the sialic acid, R. gnavus makes sure it always keeps a part of the cake for itself. This strategy contributes to its success in colonising the mucus layer and is likely to be behind its prevalence in the human gut microbiota.”

Ruminococcus gnavus is found in the guts of 90 % of the people. However, in some cases its population may reach problematic levels. Understanding survival mechanisms of our gut microorganisms may help us creating new therapies for a variety of conditions, including the inflammatory bowel disease. Human health depends heavily on the gut microbiota. Different studies have shown that gut microbiota affect heart condition, immune system, digestive function and many other systems in our bodies.

Selfishness may work well for R. gnavus, but it is not always the answer. Symbiosis, when two organisms benefit from each other, and social animals, such as humans, show that staying together is sometimes more beneficial for survival.

 

Source: University of York

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