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Of ethnicity, environment, and microbiota

Cellular & Molecular Immunology volume 16, pages 106–108 (2019)Cite this article

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In a recent study, Deschasaux et al.4 have used the second-generation sequencing to analyze the V4 hypervariable region of the bacterial 16S ribosomal RNA (rRNA) gene in the fecal matter of 2084 participants consisting of the Dutch and immigrant populations—Ghanaians, Moroccans, African Surinamese, South-Asian Surinamese, and Turkish.4 Principal coordinate analysis indicated that ethnicity significantly contributed to the inter-individual dissimilarities (β-diversity) at the operational taxonomic unit (OTU) level. Similarly, the richness and evenness of bacterial composition and α-diversity (Shannon diversity index) also differed dramatically among various ethnicities. The strongest determinant of α- and β-diversity remained ethnicity and none of the other factors including dietary patterns, age, gender, education, body mass index, lifestyle, area of residence, sample collection, and sequencing run appeared to have an effect on microbial taxa distribution in analyzed samples. Since a previous study suggested an association between fecal microbiota and metabolic syndrome, type 2 diabetes,5 a restricted number of participants without this metabolic syndrome were also analyzed, which reiterated similar ethnic patterns in α- and β-diversity.4 Notably, the Dutch displayed the highest α-diversity in contrast to the ethnic groups who immigrated from non-Western countries. Several bacterial families were highly represented in the Dutch which were depleted in South-Asian Surinamese. Overall, distinct OTUs were mutually associated with one or other ethnicities, indicating that the ethnic origin of individuals could be a marker for differences in the fecal microbial composition. This is consistent with a previous report of ethnic-specific fecal microbial taxa distribution in Chinese patients with ulcerative colitis.6

Many studies indicated that although a proportion of the microbial taxa is heritable, they are subject to modulation by environmental cues. A recent investigation of a highly homogeneous ancestry (99% Han Chinese) allowed the isolation of the effect of geography without ethnicity as a confounding factor.7 In this study, the 16S rRNA gene V4 hypervariable region was analyzed on stool samples from 7009 individuals from 14 districts within one province of China. Geographic location dominated the variation among the ‘healthy’ microbial taxa found in controls. It also exceeded the common metabolic diseases such as type 2 diabetes, obesity, and fatty liver. Importantly, extrapolation of healthy reference baselines of fecal microbiota derived from one location to others led to incorrect healthy status predictions even in a population of highly homogeneous ancestry. Thus, these data are in support of the influence of the environment on the fecal microbial composition. Further support for this notion comes from the work of Rothschild et al.8 who analyzed 1046 healthy Israeli individuals of different ancestral origins—Ashkenazi, North African, Middle Eastern, Sephardi, Yemenite, and admixed ancestries who shared a common environment. Although a previous study indicated that 42 single-nucleotide polymorphisms (SNPs) in the peripheral blood-derived DNA could be associated with 10% of the β-diversity variance in the fecal matter,9 similar analysis by Rothschild et al.8 did not result in a statistically significant outcome.8 Principal coordinate analysis indicated no significant correlation between any of the top five host genetic groups and any of top five microbiome β-diversity. No significant differences between ancestries in microbiome composition, Shannon diversity index (α-diversity), or abundance of specific taxa and evenness were observed at the phylum level. Significant similarity among microbiomes of genetically unrelated individuals who shared a household but not among the relatives who lived in different dwellings was evident. Correlation between phenotypes based on metabolic parameters such as obesity and blood glucose levels and microbial taxa found in the stool reinforced the idea that host genetics and environment are independent of each other.

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Acknowledgements

Arathi Jayaraman is acknowledged for critical comments on the manuscript.

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  1. Department of Surgery, University of Illinois College of Medicine at Peoria, Peoria, IL, USA

    Sundararajan Jayaraman

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Correspondence to Sundararajan Jayaraman.

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Jayaraman, S. Of ethnicity, environment, and microbiota. Cell Mol Immunol 16, 106–108 (2019). https://doi.org/10.1038/s41423-018-0179-8

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