Geographical variation of human gut microbial composition.

Area of Science:

• Microbiology
• Human Ecology
• Human Genetics

Background:

• Gut microbial composition exhibits significant variation within host species, but the drivers and reasons for this variation remain largely unknown.
• In humans, obesity is linked to altered proportions of dominant bacterial phyla, specifically an increase in Firmicutes and a decrease in Bacteroidetes.
• Bergmann's rule suggests that body mass increases in colder climates, implying a potential geographical influence on human physiology.

Purpose of the Study:

• To investigate the relationship between geographical latitude and the relative abundance of Firmicutes and Bacteroidetes in the human gut microbiome.
• To determine if human gut microbial composition follows patterns consistent with Bergmann's rule regarding adaptation to colder climates.

Main Methods:

• Analysis of gut microbial composition from 1020 healthy individuals across 23 populations, utilizing data from six published studies.
• Statistical correlation analysis to assess the relationship between latitude and the abundance of Firmicutes and Bacteroidetes.
• Exploration of potential confounding factors including sex, age, and bacterial detection methods, as well as host genotype comparisons.

Main Results:

• A significant positive correlation was observed between the proportion of Firmicutes and increasing latitude.
• A significant negative correlation was found between the proportion of Bacteroidetes and increasing latitude.
• The observed patterns remained robust across different sexes, age groups, and bacterial detection methodologies, and host genotype did not appear to explain the geographical variations.

Conclusions:

• Human gut microbial composition, specifically the ratio of Firmicutes to Bacteroidetes, demonstrates a clear correlation with geographical latitude.
• These findings support the hypothesis that human gut microbiome variations may be influenced by adaptations to large-scale geographical and climatic factors, consistent with Bergmann's rule.
• The study highlights a novel link between geography and human gut microbial ecology, warranting further investigation into the underlying mechanisms and implications.