Scientists have shown that the environment of the small intestine in mice can protect gut microbes against the antibacterial effects of soybean oil, according to a study in eLife.
The results have important implications for understanding the influence of dietary factors on the makeup of our healthy gut microbiome, and how this may affect the success of treatments aimed at manipulating the microbiome in diseases such as metabolic syndrome and Crohn’s disease.
Consumption of soybean oil, a common constituent in vegetable oil, has dramatically increased in the western world during the twentieth century. One of the dominant components is linolenic acid, which has been shown to prevent the growth of beneficial gut bacteria cultured in the lab.
“Although one strain of lactobacilli declined around the same time as the introduction of soybean oil, lactobacilli in general have persisted in the human gut,” says lead author Dr Sara Di Rienzi, who worked on this study while a postdoctoral researcher with senior author Professor Ruth Ley at Cornell University, US. (Di Rienzi is now at Baylor College of Medicine, US, while Ley is Director of the Department of Microbiome Science at the Max Planck for Developmental Biology, Germany). “This suggests there are mechanisms that protect against the toxic effects seen on lactobacilli exposed to components of soybean oil in the lab. We wanted to explore whether it is the lactobacilli themselves that are able to adapt to the linoleic acid in soybean oil or if the gut environment provides protection.”
The team grew strains of lactobacilli from humans and a variety of different animals in the lab, and then exposed particularly sensitive strains to linolenic acid to see if they could develop resistance to it. They then compared this with lactobacilli in the small intestine of mice fed diets low or high in soybean oil for ten weeks to mimic chronic dietary exposure. They also gave the mice a one-off high dose of linolenic acid by mouth, to study the effects of acute exposure.
Like previous studies, they found that growth of the lactobacilli was slowed by exposure to linolenic acid, but that the bacteria acquired mutations in genes that help them develop resistance to linolenic acid over time.
However, by contrast, the mice fed low or high soybean oil had roughly the same amounts of lactobacilli present in their small intestines. The microbes also survived the single high dose of linolenic acid, which was double the amount the mice would normally encounter in their total daily diet.
The results suggest that fats such as linolenic acid have only a minor effect on the microbiome. This is different from the effects of fat seen in microbial systems engineered for waste disposal, where similar concentrations of linolenic acid affect the bacteria to such an extent that the waste breakdown processes fail. It suggests that the resistance of lactobacilli to linolenic acid in the mouse is mainly due to the complexity of the small intestine habitat that the bacteria are living in.
“We have shown that the host gut environment can protect gut microbes from the growth inhibitory effects of fats, but that the microbes can also develop resistance themselves, providing additional resilience,” explains Ruth Ley. “Future work will explore exactly how this host environment protects gut microbes from otherwise toxic dietary components.”
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This research will be included in eLife’s upcoming Special Issue on mechanistic microbiome studies. To be alerted as new papers are published as part of this Special Issue, please sign up here.
To speak to senior author Ruth Ley, please contact her at ruth.ley@tuebingen.mpg.de.
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eLife
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Max Planck Institute for Developmental Biology
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eLife aims to help scientists accelerate discovery by operating a platform for research communication that encourages and recognises the most responsible behaviours in science. We publish important research in all areas of the life and biomedical sciences, which is selected and evaluated by working scientists and made freely available online without delay. eLife also invests in innovation through open-source tool development to accelerate research communication and discovery. Our work is guided by the communities we serve. eLife is supported by the Howard Hughes Medical Institute, the Max Planck Society, the Wellcome Trust and the Knut and Alice Wallenberg Foundation. Learn more at https://elifesciences.org/about.
About the Max Planck Institute for Developmental Biology
The Max Planck Institute for Developmental Biology, home of the Nobel Laureate Christiane Nüsslein-Volhard, conducts basic research in the fields of biochemistry, genetics and evolutionary biology. It employs about 360 people and is one of four Max Planck Institutes on the Max Planck Campus in Tübingen. The Max Planck Society for the Advancement of Science supports 84 independent institutes.
