There is no denying from the mountains of accumulated evidence that the trillions of microbes in our gut are important to our health. But as scientists begin to delve deeper into this relationship, they are discovering some interesting nuances – such as some species of gut microbes do not need a large presence to wield power.

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When they put both types of bacteria together into germ-free fish in a ratio of 90% and 10%, the researchers found the inflammatory response was controlled by the minority.
Image credit: Annah S. Rolig/University of Oregon

The important discovery is the subject of a Cell Host & Microbe study from the University of Oregon in Eugene. The researchers suggest their findings could lead to ways of predicting – and perhaps even preventing – disease through learning how each species of gut bacteria regulates health.

The researchers used zebra fish in their study. They introduced gut bacteria found in healthy zebra fish one type at a time and also in combination into individual fish with germ-free intestines. They monitored the effect of this by measuring bacterial abundance and the response of neutrophils – the most prolific type of white blood cell in the immune system.

An important observation was that some types of bacteria appear to have a much bigger effect. For example, the genus Vibrio generated a rapid inflammatory response, while the genus Shewanella barely attracted any.

When the researchers put both types of bacteria together into germ-free fish in a ratio of 90% Vibrio and 10% Shewanella, the inflammatory response was controlled by the minority population.

First author Dr. Annah S. Rolig, a molecular biology researcher, says:

“Until now, we’ve only been able to capture proportional information, like you’d see displayed in a pie graph, of the makeup of various microbiota, in percentages of their abundance. Biologists in this field have typically assumed an equal contribution based on that makeup.”

In studying diseases linked to gut bacteria, scientists have regarded slight shifts in the abundant species as being important factors in obesity, diabetes and inflammatory bowel diseases such as Crohn’s disease. The role of minority species has been somewhat overlooked.

Dr. Rolig says that view is now changing, as scientists begin to understand that the impact of bacteria is not necessarily determined by how many cells are present. “There is a per-capita effect that needs to be considered,” she notes.

On further investigation, the team found the low-abundant species of bacteria appear to secrete molecules – yet to be identified – that dampen the size of immune response that the whole community triggers in the gut.

The paper also describes how the team used a math-driven model, developed by one of the members, to generate formulas that predict collective inflammatory responses of combinations of bacteria.

The researchers say their study findings and the model could be generalized to more complex organisms such as humans and used to predict disease severity. For example, in people with inflammatory bowel disease, examining cell cultures of their gut bacteria could help determine the strength of their pro-inflammatory effect.

Dr. Rolig concludes:

Now we’ve shown that these minor members can have a major impact. If we can identify these keystone species, and find that in a disease state one species may be missing, we might be able to go in with a specific probiotic to restore healthy functioning.”

In another study that Medical News Today reported recently, researchers investigating effects in mice found that through interaction with intestinal bacteria, different dietary fatty acids may influence flare-ups in multiple sclerosis and autoimmune disease differently.