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Certain gut bacteria may be able to help relieve constipation. Dave and Les Jacobs/Stocksy
  • The makeup of the gut microbiome has been linked to a number of conditions, including depression, menopause symptoms, and autoimmune disease.
  • Studying the gut microbiome involves studying the genomes of bacteria, viruses, and fungi.
  • A team of researchers in China have determined that a particular gene cluster on a bacteria that lives in the gut is responsible for improved metabolism of a particular sugar and relieves constipation in humans and mice.

Twenty years on from the completion of the Human Genome Project, deciphering the significance of the human microbiome genome is the next big hurdle for scientists to climb.

Decreasing the time it takes to sequence the genome has led to a number of breakthroughs in our understanding of the influence of human genetics on our health. It has also made sequencing the genomes of the myriad organisms that make up our microbiomes possible.

Microbiome is the term used to describe the collection of microbes, including bacteria, fungi, viruses, and their genes, that live in and on our bodies — for example on our skin, and our gut.

The gut microbiome and its dysbiosis (an imbalance in bacteria) has been linked to a range of conditions, including mental health, heart disease, menopause, autoimmune disease, and a variety of gut conditions, including inflammatory bowel disease and constipation.

Despite these findings, there have been few breakthroughs that have demonstrated how and if the gut microbiome can be altered in a way that improves health. Fecal transplants have been used to repopulate the gut with potentially beneficial bacteria in people who have significant dysbiosis, for example, Clostridioides difficile infection. Meanwhile, research into the value of probiotics for improving the microbiome has remained largely inconclusive.

Now, a group of scientists have determined that a particular strain of a bacterium called Bifidobacterium longum, or B. longum, can help improve chronic constipation with no known underlying cause.

The researchers have published their results in Cell Host and Microbe.

Scientists analyzed 354 fecal samples of individuals ages 0–108 from 17 provinces in China. They isolated 185 B. longum strains and sequenced their genomes. They then identified a genetic cluster that improved the use of a certain plant-based sugar called arabanin. They named this abfA cluster.

Study author Dr. Shi Huang, from the University of Hong Kong, China, told Medical News Today: “Bacterial metabolic functions are shaped by their genetic background or genome. Gene clusters refer to groups of genes that are physically close to each other in a genome and often function together in a coordinated manner.”

“These clusters can be involved in specific biological processes, pathways, or functions. In bacteria, gene clusters can play a crucial role in various cellular activities, such as the synthesis of certain metabolites, antibiotics, or other specialized functions,” he further explained.

The presence of these clusters was due to the environmental pressures in the gut and the adaptations the bacteria made to be able to use the sugars present for fuel, he explained.

Next, researchers performed fecal transplants with donations from healthy human donors, with either a high level of B. longum strains with the abfA clusters or a low level and transplanted them into mice that had constipation induced with a drug called loperimide.

Their findings showed that mice transplanted with abfA-cluster-abundant feces had their constipation alleviated, the whole gut transit time decreased by 50 minutes, and fecal output increased in the same mice.

The researchers recruited a cohort of 87 elderly individuals over the age of 65 from a single hospital in China who had been diagnosed with functional constipation. These participants were then divided up into four treatment groups. They were randomly assigned to receive either a placebo or one of three strains of B. longum, 1,6, or 8.

They completed questionnaires about their basic health information, dietary structure, and living condition on the first visit to the clinic. Then, they filled out questionnaires about the symptoms of their constipation on each return visit. Researchers then collected their stool samples.

Supplementing with B. longum strains carrying the abfA-cluster boosted the utilization of arabanin, raised bacterial metabolites, and improved constipation symptoms in participants.

“The abfA cluster is a gut-microbiome therapeutic target for constipation in humans. More broadly, the results suggest that genetic factors governing the unique metabolic capability of probiotics should be primarily considered for screening probiotics or inferring their treatment efficacy for gastrointestinal diseases.”
— Dr. Shi Huang

“The abfA gene cluster plays a crucial role in the efficacy of probiotics in treating functional constipation (FC), by governing the utilization of dietary arabinan, a significant portion of pectic polysaccharides in various plant tissues. Understanding these genetic factors can lead to more effective probiotic therapies,” Dr. Huang said.

Alison Clark, registered dietitian and British Dietetic Society spokesperson, told MNT in an interview that she had reservations around the age of the human participants, who were all over the age of 65. It would not be possible to extrapolate these findings to younger people, or indeed to people who are not Chinese or who do not live in China, due to different diets and heritage.

She also said that probiotics are not currently recommended for constipation but there are other dietary factors that count, such as choosing whole grains.

“And then we’ve got things like, obviously, fruit and vegetables, and if we can try for fruit that are high in sorbitol that would be good like apples, apricot, grapes and raisins, peaches, pears, plums, raspberries, and strawberries. That would be really good. But if we can act on five fruit and veg as a minimum a day if possible,” she said.

Clark added that with regard to supplements, products such as psyllium husk were available and helpful.