Abstract
Delivery mode (natural vs. cesarean) and feeding type (breast vs. formula feeding) are relevant factors for neonatal gut colonization. Biomolecular methods have shown that the ecological structure of infant microbiota is more complex than previously proposed, suggesting a relevant presence of unculturable bacteria. It has also been postulated that among unculturable bacteria, hydrogenotrophic populations might play a key role in infant health. Sulfate-reducing bacteria (SRB), acetogens, and methanogenic archaea use hydrogenotrophic pathways within the human colon. However, to date, few studies have reported detection of hydrogenotrophic microorganisms in newborns, possibly because of limitations on available group-specific, culture-independent quantification procedures. In the present work, we analyzed 16 fecal samples of healthy babies aged 1–6 months by means of quantitative PCR (qPCR) targeting the 16S rRNA or metabolic functional genes and by denaturing gradient gel electrophoresis (DGGE). qPCR data showed quantifiable levels of methanogens, SRB, and acetogens in all samples, indicating that the relative abundances of these microbial groups were not affected by delivery mode (natural vs. caesarian). DGGE revealed a high prevalence of the Blautia genus within the acetogenic bacteria despite strong interindividual variability. Our preliminary results suggest that hydrogenotrophic microorganisms, which have been a neglected group to date, should be included in future ecological and metabolic studies evaluating the infant intestinal microbiota.
Highlights
Hydrogenotrophic microorganisms inhabiting the gut microbiota of humans and non-human animals are involved in a mutualistic relationship
Quantitative PCR assays were performed to evaluate the numbers of acetogens, Clostridium cluster XIVa, Blautia spp., total archaea, methanogens, sulfate-reducing bacteria (SRB), and total bacteria in fecal samples
We found a higher abundance of acetogens, as assessed both by acsB and fhs gene quantification, compared with both methanogenic archaea and SRB
Summary
Hydrogenotrophic microorganisms inhabiting the gut microbiota of humans and non-human animals are involved in a mutualistic relationship. Methanogens were detected in 10 out of 40 children (aged 3 months to 10 years), but their levels could not be precisely measured because the 16S rRNA gene density was below the assay’s lower detection limit [4]. By using quantitative PCR (qPCR), Palmer et al [5] detected archaeal 16S rRNA gene sequences in 7 out of 14 samples from 1-year-old infants. Archaeal presence has been identified in feces samples collected from birth to age 2.5 years [7]. Methanobrevibacter smithii is the dominant species detected in the human gut microbiota [8]. M. smithii was detected in all fecal specimens collected from 16 children up to the second year of life, including one sample gathered from a 2-week-old infant [9]. Previous studies found no evidence of a possible correlation between intestinal archaeal colonization in newborns and dietary habits [10], but a potential, direct mother-to-child transmission has been hypothesized [5]
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