Battling bugs may help keep people's guts healthy

"Competition between different bacteria species in the gut is what keeps humans healthy," BBC News reports. 

Research suggests this competition – as opposed to co-operation, which many have assumed was the case – helps with digestion and boosts immune function.

This study explored the factors that influence the stability of the community of "friendly" bacteria that live in our gut – something thought to be central to keeping us healthy.

Up until now, we have lacked a clear understanding of what underlies this stability. It seems competition between different microbes, rather than co-operation, leads to a more stable gut environment.

At this stage, these are only hypotheses and may not provide the whole answer. There is also nothing presented in the study that someone could do to try to beneficially influence the balance of bacteria in their gut, such as through their diet or by taking certain types of probiotics.

The study may have few current practical implications, but is nevertheless valuable in furthering our understanding of what supports a healthy balance within the human gut, and could possibly lead to new insights in the future. 

Where did the story come from?

The study was carried out by researchers from the University of Oxford and the Graduate University for Advanced Studies in Japan, and was published in the peer-reviewed journal Science Magazine.

It was funded by the European Research Council, the Engineering and Physical Sciences Research Council, the Japan Society for the Promotion of Science, and the Goldschmidt family.

BBC News provides reliable coverage of this research. 

What kind of research was this?

The researchers discuss ecological theories to help understand microbiome stability in the human gut.

Microbiome refers to all the "friendly" bacteria that live within the human digestive tract. These bacteria are thought to bring many health benefits, such as helping break down our food, supporting our immune system, and helping to protect us against any disease-causing microbes that may get into the gut.

The gut microbiome is known to be quite stable, with each person tending to carry the same set of bacteria for long periods of time. This stability is thought to be essential to maintain our health and wellbeing, but is currently poorly understood.

The researchers aimed to better understand the general principles of microbiome stability, and identify ways we can promote stability in our gut.  

What do the researchers discuss about microbiome stability?

A person and their gut bacteria need to exist in a mutually beneficial way – it is not good for the survival of the bacteria if the host dies, for example.

The researchers say it seems intuitive to many scientists that co-operation between different microbes would support this relationship, while competition would impair it.

For example, bacteria competing with each other often secrete chemicals to kill or disable one another's growth, whereas those that co-operate secrete mutually beneficial chemicals, helping all to prosper.

The researchers expected that having highly diverse bacterial species in the gut would lead to greater instability within the microbiome.

However, they found interactions between microbes could be purely co-operative, purely competitive, or a mixture of the two. Influencing the level of co-operation between diverse microbes could be expected to lead to greater stability.

The researchers used ecological network theory to investigate gut bacteria stability. They measured stability in the gut bacteria by looking at:

• the likelihood a microbe population will return to its previous stable state after a small disturbance
• how long it took to return to normal
• the dynamics of the population during this return – which species were killed or severely depleted before bouncing back, which bacteria species out-competed the rest, etc

The researchers say, contrary to what would be expected, increasing co-operative interactions actually destabilises the microbiome. Increasing the number of co-operative interactions decreases the overall return rate and the likelihood of stability.

This is because although co-operation may support the survival and replication of a different species, and help facilitate their colonisation, it also creates dependency that could lead to mutual downfall. That is, an effect on the numbers of one species could pull others down with it, and so destabilise the whole system.

The researchers suggest the host organism – that is, humans – faces a trade-off. Increased co-operation between different microbes may help improve metabolic efficiency in the gut, but it comes with the risk of instability. It seems a competitive gut environment is in fact stabilising.  

What can we do to promote stability?

The researchers next considered how we can use these principles to better understand how a host organism interacts with its gut microbes.

The researchers suggest one way the host can weaken between-species interactions, and so decrease co-operation, is through the introduction of spatial structure. They predict that, "A host can benefit from compartmentalising species within gut communities to control interactions and limit the risk of extinctions."

Another method is to do with what we eat. What we eat is expected to be able to promote the stability of microbe communities, provided it weakens co-operative interactions. For example, this could be achieved by providing different nutrients for the different bacteria to feed off, so they are not all dependent on the same energy source.

How any individual could actually go about making any conscious efforts to influence these things isn't apparent from this study.   

How did the researchers interpret the results?

The researchers say they have "developed a body of theory to identify key principles underlying microbiome stability". They have also looked at how these principles allow them to try to rethink the key features of host biology, including spatial structuring and host feeding of microbes. 

Conclusion

This study explored the factors that influence the stability of the community of "friendly" bacteria that live in our gut – something thought to be central to keeping us healthy. To date, there has been little understanding of what underlies this stability.

This study suggests competition, rather than co-operation, between different microbes leads to a more stable gut environment. The researchers discussed how humans might manipulate this, and weaken the co-operative interactions between microbes to their benefit. Possible ways of doing this include through what we eat and drink, and compartmentalising microbes within the gut.

However, though these ideas are discussed in this research, there is nothing presented at this stage that someone could actually do to try to influence their gut balance. This research isn't trying to provide practical advice for people whose gut balance may have been upset through illness or antibiotic use, for example.

As the researchers say, it is difficult for a host to exercise control over individual microbe species in their gut. Much further study, delving deeper into the nature of interactions between the main groups of microbes in the gut, will be needed to better understand how we can manipulate this.

This study only presents hypotheses, and we do not know whether other existing or future research in this area may give conflicting findings. Although the study has little current practical implications, it is valuable in furthering our understanding of what supports a healthy balance within the human gut.