What is already known on this topic
Alterations of the gut microbiota have been linked to a number of human diseases. However, consistent signatures of altered gut microbiota are lacking, likely because the human microbiota changes over time in response to external perturbations and biological processes.
What this research adds
For one year, researchers analyzed the gut microbiota of 75 people living in Sweden. They found that 23% of microbiota variation occurred in the same individual over time. People with a highly variable gut microbiota had lower abundances of Faecalibacterium prausnitzii, a butyrate-producing microbe with anti-inflammatory effects, as well as Bifidobacterium longum and Bifidobacterium breve, two human bifidobacteria with immune-modulatory functions. In contrast, the abundance of bacteria such as Escherichia coli and Lactobacillus acidophilus varied extensively within individuals.
Conclusions
The findings suggest that the human gut microbiota isn’t stable in adulthood, so reliable quantifications require repeated samples to address variations that occur in the same individual over time.
Alterations of the gut microbiota have been linked to a number of human diseases, but consistent signatures of altered gut microbiota are lacking. A new study may explain why: by analyzing stool samples from dozens of people in Sweden, researchers have found that the microbiota isn’t stable in adulthood.
The findings, published in Cell Host & Microbe, highlight the need to collect repeated samples to address variations that occur in the same individual in order to obtain reliable quantifications of microbiota alterations.
“Our study underscores the importance of the temporal dynamics of gut microbiota for gut microbiome research and the need for localized longitudinal investigations in well-defined populations to assess the value of potential biomarkers for health or disease, particularly among features with high intra-individual bias,” the researchers say.
Several studies have suggested that the microbiota could be used as a biomarker for diagnosing diseases and developing new therapeutic approaches. However, the lack of consistent signatures of microbiota alterations limit our understanding of the role of gut microbes in human diseases.
To characterize the temporal dynamics of the gut microbiota under stable conditions, researchers led by Valentina Tremaroli and Fredrik Bäckhed at the University of Gothenburg analyzed the gut microbiota of 75 Swedish people aged 50 to 65 years.
Microbiota-stabilizing bacteria
The study participants were screened at four visits over one year and did not receive antibiotics. The researchers found 184 bacterial species that were present in all samples. The analysis confirmed that the gut microbiota is individualized, but 23% of microbiota variation occurred in the same individual over time.
The degree of variability in gut microbiota composition differed between study participants. People with a highly variable gut microbiota had lower abundances of Faecalibacterium prausnitzii, a butyrate-producing microbe with anti-inflammatory effects, as well as Bifidobacterium longum and Bifidobacterium breve, two human bifidobacteria with immune-modulatory functions.
“F. prausnitzii, B. longum, and B. breve might be markers of stable communities and/or possible stabilizing factors of the gut microbiota in our population,” the researchers say. The team hypothesizes that human genetics and diet may influence the abundance of B. longum and B. breve, which may in turn affect the stability of the whole microbiota community through their anti-inflammatory properties and interaction with the immune system.
Intra-individual variation
The team observed the largest variance, both across and within individuals, for bacteria such as Akkermansia muciniphila, Prevotella copri, Lactobacillus acidophilus and Escherichia coli. The abundance of E. coli and L. acidophilus varied extensively between consecutive visits of the same study participants, the researchers found. This suggests that “occasional blooming of these species is a normal feature of the human gut microbiota,” they say.
The team also validated the results in an independent group of 62 healthy people. The 20 most dominant species in this group included Bacteroidetes, Parabacteroides, Alistipes and F. prausnitzii.
“Reliable determination of abnormal abundances might be challenging for species with large intra-individual variation, and study designs with repeated sampling or observation of large effect sizes in large samples might be required to draw reliable conclusions for associations with health or disease states,” the researchers say.
