Inverse Association between Serum Vitamin B₁₂ Level and Abundance of Potential B₁₂-Producing Gut Microbes in Indian...

The human gut microbiome is a natural source of essential micronutrients like B vitamins, which are used by both the host and other community members. The prevalence and abundance of known B-vitamin producers and B-vitamin biosynthesis pathways have already been reported in gut microbiome cohorts of a few countries including India.

This study tested whether the presence of B-vitamin producers/biosynthetic pathways associates with serum B-vitamin levels, taking vitamin B₁₂ as a case example.

Fecal samples were collected from non-deficient (serum vitamin B₁₂ level > 210 pg/mL; n = 29) and vitamin B₁₂ deficient (serum vitamin B₁₂ level < 210 pg/mL; n = 30) children from a tribal region of central India. Whole metagenomic DNA was extracted, sequenced, and analyzed for taxonomic profiling and diversity comparisons. Differentially abundant taxa between two groups were identified. The prevalence and abundance of potential vitamin B₁₂ producers were compared, and their association with serum vitamin B₁₂ level was established.

A comparison of within-sample diversity between the two groups did not show any difference; however, between-sample diversity was significantly less in the vitamin B₁₂-deficient group. Differential abundance testing also showed different microbiome structure in the vitamin B₁₂-deficient group, where a higher abundance of vitamin B₁₂ transporter-carrying Bacteroides thetaiotaomicron, a few pathogenic species, and ten known vitamin B₁₂ producers was observed. Potential vitamin B₁₂ producers were also significantly prevalent and abundant in the deficient group. Their cumulative abundance was also significantly higher in the deficient group and showed a negative association with serum vitamin B₁₂ levels.

A higher abundance of potential vitamin B₁₂ producers in the deficient group suggest an adaptive mechanism by the gut microbiome to meet the community's vitamin B₁₂ requirements, by selectively promoting the growth of vitamin B₁₂ producers, but causality remains to be proved.