Expanding the cultivable human archaeome: Methanobrevibacter intestini sp. nov. and strain Methanobrevibacter smithii ‘GRAZ-2’ from human faeces (April 2025) Archaea

[NiroZ]

https://phys.org/news/2025-04-microbiologists-species-methane-archaea-human.html
https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijsem.0.006751

The new species Methanobrevibacter intestini WWM1085 clearly differs genetically and physiologically from all previously known species. It thrives exclusively under strictly anaerobic conditions and produces methane and surprisingly large amounts of succinic acid, a metabolic product that is associated with inflammatory processes in the human body.


The second strain that was discovered, a variant of Methanobrevibacter smithii referred to as GRAZ-2, exhibits unusual features: It produces formic acid, a molecule that may interfere with the metabolism of other gut inhabitants.

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"Our discovery is a further piece in the puzzle towards understanding how the human microbiome functions," explains Christine Moissl-Eichinger, Professor of Interactive Microbiome Research at Med Uni Graz. While microbiome research focuses on bacteria, archaea have eked out a shadowy existence—in spite of their potentially great influence on key metabolic processes in the human body.

"Archaea have long been overlooked," says Moissl-Eichinger. "They may play a significant role in gut function, microbial gas metabolism and possibly even the development or progression of certain diseases."

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ABSTRACT

Two mesophilic, hydrogenotrophic methanogens, WWM1085 and M. smithii GRAZ-2, were isolated from human faecal samples. WWM1085 was isolated from an individual in the United States and represents a novel species within the genus Methanobrevibacter. M. smithii GRAZ-2 (=DSM 116045) was retrieved from a faecal sample of a European, healthy woman and represents a novel strain within this species. Both Methanobrevibacter representatives form non-flagellated, short rods with variable morphologies and the capacity to form filaments. Both isolates showed the typical fluorescence of F420 and methane production. Compared to M. smithii GRAZ-2, WWM1085 did not accumulate formate when grown with H2 and CO2. The optimal growth conditions were at 35–39 °C and pH 6.5–7.5. Full genome sequencing revealed a genomic difference of WWM1085 to the type strain of M. smithii DSM 861 (=PST), with 93.55% average nucleotide identity (ANI) and major differences in the sequence of its mcrA gene (3.3% difference in nucleotide sequence). Differences in the 16S rRNA gene sequence were very minor, and thus distinction based on this gene marker might not be possible. M. smithii GRAZ-2 was identified as a novel strain within the species Methanobrevibacter smithii (ANI 99.04% to M. smithii DSM 861 [=PST]). Due to the major differences between WWM1085 and M. smithii type strain M. smithii DSM 861 (=PST) in phenotypic, genomic and metabolic features, we propose Methanobrevibacter intestini sp. nov. as a novel species with WWM1085 as the type strain (DSM 116060T = CECT 30992T).

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I'm sharing this mostly because it's cool that researchers managed to identify a strain of archaea, cultivate it and study it, and it highlights just how much we don't actually know about the microbiome despite intensive study of the bacteriome to the point where people often make the mistake of assuming microbiome = bacteria.

It also would have been nice to know more about the donors, all that is stated is that the second donor was a healthy 42yo woman, but they likely didn't have that information themselves.