Tag Archives: gut microbiome

Sunlight might affect gut microbiome diversity

Researchers at the University of British Columbia in Canada have found a significant link between exposure to ultraviolet rays and an increase in gut bacterial diversity. The findings could prove important in managing autoimmune diseases known to be associated with gut bacterial diversity, such as inflammatory bowel disease.

Credit: Pixabay.

Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelengths ranging from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. Our senses cannot detect UV rays — not until the damage is done — which is why they can be especially dangerous. Too much time in the sun causes sunburns, eye damage, accelerate aging, and skin cancer.

There are 2 main types of UV rays that interact with our skin.

  • UVB, which is responsible for the majority of sunburns, and
  • UVA, which penetrates deep into the skin. It ages the skin, but contributes much less towards sunburn.

Although prolonged exposure to UV radiation can be very harmful, we also require moderate exposure in order to live healthily. Research has shown a link between UV exposure and the synthesis of vitamin D, which promotes the formation and strengthening of bones (a deficiency will cause bone softening diseases, which then causes rickets in children and osteomalacia in adults), strengthens the immune system, and offers protection against some cancers.

In the study, 21 female participants received three 60-second full-body UVB exposure sessions over the course of one week. The researchers drew blood and fecal samples from each subject at the beginning and end of the trial in order to analyze changes in vitamin D and gut bacteria. Half of the participants had taken vitamin D supplements during the prior three winter months.

The subjects who didn’t take vitamin D supplements experienced an increase in alpha and beta gut microbiome diversity. They also experienced a 10% increase in blood serum vitamin D concentration after the week-long UVB exposure. On the other hand, those who took vitamin D supplements did not experience an increase in gut microbiome diversity. This suggests that vitamin D is the mediating factor between UVB exposure and gut microbial activity.

“Prior to UVB exposure, these women had a less diverse and balanced gut microbiome than those taking regular vitamin D supplements,” says lead-author Bruce Vallance, from the University of British Columbia. “UVB exposure boosted the richness and evenness of their microbiome to levels indistinguishable from the supplemented group, whose microbiome was not significantly changed.”

Although the researchers haven’t identified a formal mechanism, they think that the initial exposure to UVB light alters the immune system — first at the level of the skin, then more systematically throughout the body, affecting how bacteria interact with the environment inside the intestines. Previously, studies have shown that inflammatory bowel disease symptoms can worsen when the body experiences vitamin D deficiency, which strengthens the idea sunlight exposure and gut health are somewhat connected.

Next, the team plans on performing similar studies on a larger cohort of subjects in order to investigate this link better.

“The results of this study have implications for people who are undergoing UVB phototherapy, and identifies a novel skin-gut axis that may contribute to the protective role of UVB light exposure in inflammatory diseases like MS and IBD,” says Vallance.

The findings appeared in the journal Frontiers in Microbiology.

Probiotics are rarely actually useful — and they might sometimes be bad for you

When it comes to probiotics, it’s a bit like “the good, the bad, and the nothing” — they can do some good, they do a whole load of nothing most of the time, and, as a new study has shown — they can also do a bit of bad.

Probiotics are essentially living yeast and bacteria, which are thought to improve various aspects of your health when consumed. However, despite popular belief, the evidence that supports the benefits of probiotics is limited and often restricted to isolated cases.

In order to figure out what really happens when people ingest probiotics, immunologist Eran Elinav of the Weizmann Institute of Science in Israel, directly analyzed people’s microbiomes, after they were fed either a probiotic cocktail or a placebo. Along with colleagues, Elinav and colleagues sampled the microbiomes of volunteers directly, through endoscopies and colonoscopies — most studies were carried through proxies.

For starters, they found that faecal samples are not representative of what goes on in the gut.

“Relying on faecal samples as an indicator of what goes on inside the gut is inaccurate and wrong,” says Elinav.

Then, they found that there are major differences between individuals and probiotics greatly differ in efficiency.

The reasons which caused these differences are not clear, but the study suggests that there’s not enough justification to administer probiotics to everybody because their effect can vary so much.

“This tells us the currently used paradigm of one-size-fits-all probiotic preparation and treatment should be replaced by a tailored therapy which harnesses science and measurement and technology,” said Elinav, adding that “with this tailored approach probiotics have greater chances to benefit health”.

Then, in another study, they administered probiotics to a third group, which had previously been administered antibiotics. This was done to test whether probiotics can help the microbiome recover after a course of antibiotics — a common-held belief.

Researchers found that the probiotics readily colonized the participants’ guts, but they took over so much that the original microbiome had a hard time recovering.

“Once the probiotics had colonised the gut, they completely inhibited the return of the indigenous microbiome which was disrupted during antibiotic treatment,” said Elinav.

This would suggest that the use of probiotics is actually counter-productive in some cases.

Overall, the findings cast a big shadow over probiotics: for once, they only seem to be efficient for some people, and they’re also not always as harmless as most people think.

Journal Reference: CellDOI: 10.1016/j.cell.2018.08.04110.1016/j.cell.2018.08.047

Scientists write molecular cookbook for our gut bacteria

Scientists have written an unusual cookbook — one that’s not for humans, but rather for our microbiome.

Cookbooks for humans are aplenty, but this is the first one aimed at gut bacteria.

When scientists publish something, it’s usually complex papers about previously unknown mechanisms or processes, but today, in Nature Microbiology, scientists are putting a new spin on that: they’re publishing recipes to successfully grow and study gut bacteria in the lab. Their work will help researchers across the world to advance our understanding of gut bacteria.

Recent research has increasingly shown that gut bacteria is important for our health, with studies finding that the meager bacteria in our guts play a part in protecting against diseases, recovering from injuries, even regulating our genes. However, we know surprisingly little about how all this happens. We don’t know how it grows, how it metabolizes nutrients, and we don’t even know what kind of food it likes.

Nassos Typas and his colleagues from the European Molecular Biology Group have addressed that in their latest study. Along with Peer Bork and Kiran Patil, he selected the most common bacteria to be found in the human gut, plus important species connected to gut diseases such as colorectal cancer and inflammatory bowel disease, ending up with 96 strains from 72 bacterial species, in 19 different growth environments.

They characterized the nutritional preference of these bacteria, as well as their ability to digest and produce specific molecules. As it so often happens with studies on gut bacteria, results were quite surprising.

“We were surprised to find new bacteria with the capability to utilize mucin, the protein that makes up mucus,” says Kiran Patil. “These bacteria can contribute to inflammation and infection by weakening the protective mucus barrier lining the gut. Another surprise came from bacteria that proved to be inhibited by amino acids and short-chain fatty acids, common ingredients in most growth media. It turns out that rich media with many nutrients can be toxic for these species, whereas we used to think: the more food, the better.”

Also surprisingly, researchers found that even bacteria that are closely related to each other can have very different nutritional preferences, showing that a bacterium’s genes alone can’t predict what it likes to ‘eat.’

With this scientific ‘cookbook’ filled with molecular recipes on how to grow gut bacteria, researchers want to provide the scientific community with tools to study the structure and function of the human gut microbe. It’s clear that we need much more work before we can thoroughly understand the role and impact of gut bacteria, and this could be a major stepping stone for such future studies.

“Our resource provides scientists with tools to experimentally investigate the gut microbiome ecology, going beyond correlations and identifying causes and effects,” says Nassos Typas.

Journal Reference: Tramontano, M., Andrejev, S. et al. Nutritional preferences of human gut bacteria reveal their metabolic idiosyncrasies. Nature Microbiology, published online 19 March 2018.