UNL Scientists Studying Gut Microbes' Relationship with Hosts


University of Nebraska-Lincoln scientists trying to understand how microorganisms in the gastrointestinal tract influence human health are learning more about how the relationships between microbiota and their vertebrate hosts have evolved, with an eye toward how modern lifestyles affect the microbial populations in the human gut.

The research, which is one facet of UNL's Gut Function Initiative, recently was featured in the Proceedings of the National Academy of Sciences in an article co-written by gastrointestinal microbiologist Jens Walter.

The Gut Function Initiative, featuring a team of about 12 scientists from across the university, aims to unlock the mysteries of the gastrointestinal tract and, ultimately, transform that understanding into practices and products - including what some call "designer foods" - that might help address obesity, disease and other concerns.

Walter's research about which he wrote for PNAS focuses on the symbiotic relationship between host organisms - mammals and birds - and their microbial symbionts in the gastrointestinal tract, with a focus on Lactobacillus reuteri, a bacterium found in the gut of mammals and birds that's known for many positive health effects.

"We learn more and more about what the microbiota does but we don't know a lot about how that relationship evolved and the biological principles that govern this partnership," Walter said.

One question scientists are trying to resolve: While both hosts and gut microbes have evolved, was their respective evolution coincidental or did they "coevolve," specifically adapting to each other along the way? By using studies with Lactobacillus reuteri, UNL scientists could show that some gut microbes remain firmly associated with particular groups of vertebrate hosts, including humans, over evolutionary time.

Lactobacillus reuteri has a number of benefits when present in the GI tract. Past studies have shown it helps modulate the host's immune system. One study showed it improved infants' health in a day-care setting; it's also been shown to reduce symptoms of colic.

These beneficial effects of Lactobacillus reuteri"might be a direct consequence of its shared evolutionary fate (and potentially coevolution) with groups of vertebrate hosts," Walters wrote in the article.

Research has shown L. reuteri was more prevalent in humans 50 years ago than it is today. That may be because humans' lifestyle has changed, including increased use of antibiotics, development of highly refined diets and other features such as hygiene and the prevalence of cesarean sections.

"What we do today in modern western society is virtually everything possible to prevent the natural or healthy transmission of these microbial communities between generations," Walter said. That may explain why so-called "lifestyle diseases" that are associated with aberrations of the gut microbiota have become more prevalent in recent decades.

"Every symbiosis is reliant on the environmental conditions in which these organisms live," he added. For example, while antibiotics have been key in fighting pathogenic bacteria, they also may be harming beneficial bacteria.

"We need to understand these symbioses and how they are shaped by our environment," Walters said. "This has important implications on how we can modulate that ecosystem to benefit humans."

Ultimately, as these relationships become better understood, microbes such as Lactobacillus reuteri could be restored to humans' GI systems to improve health.

Popular medicine already is making promises in this area, with dietary supplements containing beneficial bacteria and non-digestible carbohydrates (prebiotics) heavily marketed in over the counter products. While these strategies may have some health benefits, Walter said, a more systematic selection of probiotic strains and prebiotic substrates based on an understanding of how the microbiota and hosts interact and evolve is sure to be more effective.

Other authors of the PNAS article are Robert Britton of Michigan State University and Stefan Roos of the Swedish University of Agricultural Sciences.

- Dan Moser, IANR News

More details at: http://go.unl.edu/76j