Anaerobutyricum soehngenii
Gut microbiota, butyrate and the limits of scientific evidence

After today’s piece on the EFSA opinion for strain CH106, it helps to separate strain from species. Anaerobutyricum soehngenii is a strict gut anaerobe that produces butyrate — with its own taxonomic and ecological history. This article gathers primary sources on origin, microbiota niche and what science actually shows, versus what must not be sold as claims.

1. Taxonomy: do not confuse A. soehngenii with A. hallii

The name Eubacterium hallii goes back to Holdeman and Moore (1974), who described the species from human faecal isolates. For decades, related but non-identical lineages were filed under that label.

In 2018, Shetty et al. in the International Journal of Systematic and Evolutionary Microbiology (DOI 10.1099/ijsem.0.003041) proposed the genus Anaerobutyricum within Lachnospiraceae:

• Anaerobutyricum hallii — reclassification of the E. hallii type (=DSM 3353^T=ATCC 27751^T);
• Anaerobutyricum soehngenii — new species; type strain L2-7^T (=DSM 17630^T=KCTC 15707^T), isolated from infant faeces.

The epithet soehngenii honours Nicolaas L. Söhngen, first professor of microbiology at Wageningen, for contributions to anaerobic microbiology (LPSN / IJSEM description). DNA–DNA hybridisation between L2-7 and DSM 3353 was about 26%, supporting separate species status.

2. Origin and research history

Strain L2-7 was isolated from infant faeces in work on human-gut butyrate producers (including Barcenilla et al., 2000; available from DSMZ as DSM 17630). Duncan, Louis and Flint (2004) showed that isolates then affiliated with “E. hallii” use D- and L-lactate (with acetate) to form butyrate — unlike many butyrate producers that mainly ferment sugars.

Later the complete L2-7 genome was sequenced (Shetty et al., 2017) and a lactate-utilisation gene cluster (lctABCDEF) conserved in Anaerobutyricum and Anaerostipes was characterised (Shetty et al., 2020). Wortelboer et al. (2022) review the path from FMT association toward developing this commensal as a next-generation probiotic / LBP candidate.

3. Where it occurs — gut ecology

A. soehngenii is Gram-positive, catalase-negative and strictly anaerobic. Microbiome literature treats Anaerobutyricum species as core members of the human gastrointestinal microbiota, detectable early in life. Metabolically it often acts as a cross-feeder: it consumes lactate and acetate made by other bacteria (e.g. bifidobacteria) and converts them to butyrate — a short-chain fatty acid central to gut ecology.

The L2-7 genome includes genes suggesting effects on bile-acid metabolism (bile acid sodium symporter, choloylglycine hydrolase) and vitamin B₁₂-related pathways — genomic hypotheses, not ready-made product claims.

4. Health-related actions — what science describes (carefully)

The literature does not equate to a medicinal product label. It reports, among other things:

• Gut mechanism: lactate-to-butyrate conversion may limit lactate accumulation and support the SCFA network (Duncan 2004; Louis/Flint reviews).
• Animal models: oral dosing (then labelled E. hallii) improved insulin sensitivity in db/db mice (Udayappan et al., 2016) — preclinical only.
• Humans: after lean-donor FMT in metabolic-syndrome subjects, butyrate-producing anaerobes including Anaerobutyricum-related lineages rose alongside improved insulin sensitivity (Vrieze et al., 2012) — correlation in an FMT context, not mono-strain proof.
• Mono-strain interventions: early trials with L2-7 (e.g. Gilijamse 2020 — safety and dose–glucose signals; Koopen 2022 — duodenal infusion, GLP-1, glycaemic variability) report tolerability and metabolic signals in narrow cohorts. That is not the same as established clinical efficacy “on the label”.

5. Known versus unknown

1. Comparatively well known: taxonomic placement (2018), L2-7 isolation, lactate+acetate → butyrate capacity, gut-commensal status, type-strain availability (DSMZ).
2. Partly known: bile acids / GLP-1 / glycaemia signals in exploratory studies; colonisation often transient after cessation in reported trials.
3. Poorly known / open: long-term population effects, diet and drug interactions (e.g. metformin — hypotheses in the literature), safety and efficacy outside studied groups, strain-to-strain differences within the species.
4. EU regulatory reality (as of this article’s date): the species alone does not unlock claims. Claims need the 1924/2006 pathway. A separate novel-food safety assessment applies to a specific ingredient/strain and conditions of use — for CH106 see the NDA opinion; that is still not Union-list entry or a claim.

6. What this means for market communication

You may educate about butyrate’s ecological role and taxonomic history with citations. You must not suggest product health benefits without claim authorisation. Even wording such as “contains probiotics” can be treated in the EU as a claim needing substantiation. Novel food (where applicable) and health claims are independent tracks.

Conclusion

A. soehngenii is a well-described gut anaerobe in Lachnospiraceae, carved out taxonomically in 2018 from the old E. hallii complex, with type strain L2-7 from infant faeces and a characteristic lactate→butyrate metabolism. Science provides mechanisms and early clinical signals — not a universal efficacy proof or a right to health claims. The EFSA opinion on CH106 concerns novel-food safety, not health marketing.

Primary sources

1. Shetty SA et al. Reclassification of Eubacterium hallii as Anaerobutyricum… Int J Syst Evol Microbiol. 2018. DOI: 10.1099/ijsem.0.003041 — species/genus description; PubMed 30351260.
2. Duncan SH, Louis P, Flint HJ. Lactate-utilizing bacteria… Appl Environ Microbiol. 2004.
3. Barcenilla A et al. Phylogenetic relationships of butyrate-producing bacteria… Appl Environ Microbiol. 2000.
4. Shetty SA et al. Complete genome sequence of Eubacterium hallii strain L2-7. Genome Announc. 2017.
5. Shetty SA et al. Unravelling lactate-acetate… into butyrate. Environ Microbiol. 2020.
6. Wortelboer K et al. From FMT toward next-generation beneficial microbes: A. soehngenii. Front Med. 2022.
7. Gilijamse PW et al. Treatment with A. soehngenii: pilot safety and dose–response… NPJ Biofilms Microbiomes. 2020.
8. Koopen A et al. Duodenal A. soehngenii infusion… Gut. 2022.
9. EFSA NDA Panel. Safety of A. soehngenii CH106 as a novel food. EFSA Journal 2026 — strain safety ≠ claims.
10. Regulation (EC) No 1924/2006 — nutrition and health claims.
11. LPSN: Anaerobutyricum soehngenii — nomenclatural status, type strain, etymology.