Overview

M2GSC — Modified M2 medium with Glucose, Soluble starch, and Cellobiose — is the rumen-fluid-supplemented anaerobic broth originally described by Hobson (1969) for the rumen-fermentation community, modified by Miyazaki (1997) for SCFA-utilising Firmicutes, and adopted by the Browne et al. (2016) Nature culturomics workflow at the Wellcome Sanger Institute (Lawley lab) for cultivation of previously-unculturable human gut commensals. The medium achieves what defined-recipe media cannot: it supplies the full complement of growth factors (fatty acids, branched-chain amino acids, polyamines, undefined cofactors) that fastidious Firmicutes within the Lachnospiraceae, Ruminococcaceae, and Christensenellaceae depend on for primary isolation.

The defining ingredient is clarified rumen fluid at 30 % v/v. Rumen fluid is the supernatant of fistulated-cow rumen contents (SARDI / CSIRO Armidale partners, or commercial lyophilised product), filtered, autoclaved, and lyophilised for shelf-stable supply. The medium also includes glucose 2 g/L + soluble starch 2 g/L + cellobiose 2 g/L (the GSC carbohydrate trio), sodium carbonate for CO2-headspace buffering, sodium acetate + propionate + valerate + iso-butyrate + iso-valerate (the same SCFA set as YCFA and GMM, supporting SCFA-utilising Firmicutes), L-cysteine 0.5 g/L, and the standard hemin + VK1 + resazurin set. It is the second cornerstone product (alongside GMM) for serious gut-culturomics laboratories targeting the long-tail of cultivable but neglected commensal organisms — including taxa reclassified from the historical genus Eubacterium (now distributed across Agathobacter, Anaerobutyricum, Eubacterium sensu stricto).

We also have

YCFA Modified Medium · YCFA Full Recipe · YCFA Base · Modified Chopped Meat Broth (ATCC 1490) · Chopped Meat with Carbohydrates · Beef Granules

Package Contents

Each GMExpression M2GSC kit contains:

  • Mixture A — pre-weighed M2 base (Bacto-casitone 1 g/L + yeast extract 2.5 g/L + glucose 2 g/L + cellobiose 2 g/L + soluble starch 2 g/L + sodium acetate 5 g/L + K2HPO4 + KH2PO4 + NaCl + MgSO4 + CaCl2 + Na2CO3 + resazurin) for 5 L final volume.
  • Mixture B — L-cysteine·HCl 2.5 g + Na2CO3 2 g, N2-flushed PP bag.
  • Rumen-fluid concentrate — lyophilised clarified rumen fluid, DAFF EX188M / ovine zoosanitary certified, equivalent to 1.5 L rumen fluid (= 5 L × 0.30 v/v); 5 × 300 mL-equivalent vials.
  • Stock H — Hemin stock, 25 mg in 5 mL of 0.05 M NaOH.
  • Stock K — Vitamin K1 stock, 50 mg in 5 mL of 95 % ethanol, amber.
  • Stock S — SCFA mix (propionate / iso-butyrate / iso-valerate / valerate) in oxygen-free water, glass ampoule, N2-flushed. Acetate is already in Mixture A.
  • 5 × airtight PP storage bags + 5 × heat-resistant rubber bands.
  • Instruction manual (A5 booklet, v1.0) with Hobson-1969 / Browne-2016 protocol annexes.

Customisation options on request: agar variant at 15 g/L; defined-medium analogue (R&D-grade) substituting rumen fluid with a complex defined medium (vitamin / micronutrient / undefined-cofactor pack — note: lower recovery than authentic rumen-fluid); SCFA-omitted variant for cross-feeding studies; vegan / non-ruminant alternative on request.

Composition — per 1 L equivalent unless stated otherwise

M2GSC Broth (Hobson 1969 + Miyazaki 1997 + Browne 2016 modification; per 1 L)

ComponentConcentrationFunction
Bacto-casitone (pancreatic digest of casein)1.0 gPeptide nitrogen source (low-level — most growth factors from rumen fluid)
Yeast extract2.5 gB-vitamins, NAD precursors
D-Glucose2.0 gPrimary carbohydrate (G in GSC)
Cellobiose2.0 gDisaccharide for cellulolytic / cellobiose-utilising organisms (C in GSC)
Soluble starch2.0 gPolysaccharide for starch-utilisers (S in GSC)
Sodium acetate (anhydrous)5.0 g (≡ 61 mM)Acetate for SCFA-utilising butyrate producers (cross-feeding substrate)
Clarified rumen fluid (30 % v/v final)300 mLCritical undefined growth-factor supplement — lyophilised concentrate
K2HPO4 / KH2PO40.45 g / 0.45 gPhosphate buffer
NaCl0.9 gOsmotic balance
MgSO4·7H2O0.09 gMagnesium
CaCl2·2H2O0.09 gCalcium
Sodium carbonate (Na2CO3)4.0 gCO2-headspace buffering; lowers headspace O2
L-Cysteine·HCl·H2O0.5 gReductant; Eh < −150 mV
Hemin5.0 mgRequired by Bacteroides & haem-auxotrophs
Vitamin K11.0 mgMenaquinone precursor
Resazurin1.0 mgRedox indicator

SCFA top-up (Stock S; post-autoclave addition inside AAE; final concentrations)

Short-chain fatty acidFinal concentration
Sodium propionate9 mM (0.86 g/L equiv)
Iso-butyric acid1 mM
Iso-valeric acid1 mM
Valeric acid (n-valeric)1 mM
(Acetate is already in Mixture A at 61 mM — no additional acetate needed)—

Pre-autoclaving pH: 6.8 ± 0.2 at 25 °C. Note: M2GSC's lower pH (6.8 vs 7.2 for YCFA / 7.3 for mGAM) reflects rumen-fluid physiology and favours rumen-derived organisms.

→Culturomics and Media Navigator

Need help matching this medium to your microorganism — or starting from a target organism and finding the medium that fits? Use the GMExpression Culturomics and Media Navigator: a curated, cross-referenced tool that lets you (i) start from a medium and view the bacterial taxa it is recommended for, or (ii) start from a target organism (genus, species, or DSMZ/ATCC strain ID) and view the panel of GMExpression media that will support it. The Navigator integrates Modified M2 / M2GSC Medium with the wider YCFA, Chopped Meat Broth, BHI-S, Wilkins-Chalgren, Modified GAM, Anaerobic Columbia Blood Agar, GMM, BBE, KVLB, CCFA, TPY, and Egg Yolk Agar catalogue.

Use and Applications

  • Maximum-diversity culturomics of the human gut microbiota per the Browne et al. (2016) Nature workflow (Lawley lab, Wellcome Sanger Institute). Used to culture > 130 previously-uncharacterised species from human stool.
  • Rumen microbiology research — original Hobson 1969 use case; still the standard for cultivable studies of Fibrobacter succinogenes, Ruminococcus albus, R. flavefaciens, Butyrivibrio fibrisolvens, etc.
  • SCFA-utilising butyrate producer enrichment from human stool — recovery comparable to or better than YCFA for Roseburia, Faecalibacterium, Anaerobutyricum hallii.
  • Lachnospiraceae / Ruminococcaceae / Christensenellaceae primary isolation — these clades benefit from the undefined growth-factor content of rumen fluid.
  • Bioreactor-fermentation studies of mixed gut communities — the medium supports the broadest cross-feeding network of any defined-recipe medium.
  • Sporulation / dormancy studies of spore-forming Firmicutes from the human gut (Browne et al. 2016 demonstrated extensive sporulation in this medium).

Compatible Microorganisms

Human gut commensals successfully cultured per Browne et al. 2016 Nature

  • Roseburia intestinalis, R. inulinivorans, R. hominis
  • Faecalibacterium prausnitzii (DSM 17677)
  • Agathobacter rectalis (formerly Eubacterium rectale; reclassified Rosero 2016)
  • Anaerobutyricum hallii (formerly E. hallii; reclassified Shetty 2018)
  • Anaerostipes caccae, A. hadrus
  • Christensenella minuta (DSM 22607) — heritable-microbiome flagship organism (Goodrich 2014 Cell)
  • Coprococcus catus, C. eutactus, C. comes
  • Lachnospiraceae sp. nov. (multiple, characterised in Browne 2016)
  • Mediterraneibacter gnavus (formerly Ruminococcus gnavus)
  • Spore-forming Firmicutes recovered from heat-treated stool

Rumen organisms (Hobson 1969 original use case)

  • Ruminococcus albus, R. flavefaciens — cellulolytic rumen Firmicutes
  • Butyrivibrio fibrisolvens — butyrate-producing rumen organism
  • Fibrobacter succinogenes (formerly Bacteroides succinogenes) — cellulolytic, succinate-producing
  • Selenomonas ruminantium
  • Prevotella ruminicola

General anaerobes (parallel growth)

  • Bacteroides spp., Bifidobacterium spp., Lactobacillus sensu lato (Zheng 2020 reclassification)
  • Clostridium spp., Eubacterium sensu stricto, Veillonella spp.

Preparation

1Reconstitute rumen-fluid lyophilisate. Add 300 mL of pre-reduced sterile distilled water to each lyophilised rumen-fluid vial (300 mL equivalent per litre of final medium). Allow 30 min for full dissolution at 4 °C. The reconstituted rumen fluid is dark amber-brown.
2Weigh Mixture A. Use the pre-weighed Mixture A (~16 g per litre, excluding the rumen fluid). Tare a clean autoclavable Schott bottle of at least 1.5× final volume.
3Combine. Add Mixture A to 650 mL of distilled water; heat to dissolve. Add 300 mL of reconstituted rumen fluid; mix gently.
4Add Mixture B (cysteine + Na2CO3). Open the N2-flushed Mixture B inside an AAE (or use sealed-vial septum technique). Add to the medium. Stir to dissolve.
5Add pre-autoclave supplements. Pipette 1 mL of Stock H (5 mg/mL hemin) and 0.1 mL of Stock K (10 mg/mL Vitamin K1). Swirl.
6Adjust pH. Cool briefly to ~45 °C. Verify pH; target 6.8 ± 0.2 at 25 °C. Adjust with 1 M NaOH or 1 M HCl. Note: M2GSC's lower target pH (6.8) is correct — do not adjust to 7.0 or 7.2.
7Bring to final volume. Make up to 1000 mL with distilled water.
8Dispense. Hungate tubes (5–10 mL) under N2/CO2 headspace are preferred for the Browne 2016 protocol. Leave ≥ 1 cm headspace.
9Autoclave. 121 °C × 15 min (103 kPa). Slow cooling.
10Cool, reduce, and add SCFA. Transfer to AAE while warm. Allow 24-h pre-reduction. When cooled and reduced, add Stock S (propionate + branched-chain SCFAs) inside the AAE per the lot-specific volume card.
11Recheck pH. Verify pH 6.6–7.0 after SCFA addition. Adjust if necessary with sterile 1 M NaOH.

Critical control points

  • Rumen-fluid sourcing and certification. GMExpression sources rumen fluid via SARDI / CSIRO Armidale partnerships and commercial lyophilised suppliers, all DAFF EX188M / ovine zoosanitary certified. Lyophilisation extends shelf life from 6 weeks (fresh frozen) to 24 months (lyophilised at −80 °C reconstituted as needed).
  • pH at 6.8 — do not over-adjust. M2GSC pH 6.8 is intentional (matches rumen-fluid physiology). Adjusting to 7.0 or 7.2 → reduced recovery of acidotolerant Firmicutes that the medium is designed to recover.
  • Pre-reduction time. 24 h equilibration inside the AAE is mandatory before inoculation of fastidious organisms. The CO2-headspace + Na2CO3 buffer system reaches Eh < −250 mV after 24 h.

Cautions

Rumen-fluid sourcing. Rumen fluid is a complex undefined biological material with batch-to-batch variability. GMExpression's lyophilised supply pools rumen fluid from multiple donor animals to reduce inter-batch variability. Recovery performance is QC-tested with the Browne 2016 reference taxa (e.g., Christensenella minuta).
Defined-medium analogue is R&D-grade only. The defined-medium alternative (no rumen fluid) is available for facilities that cannot use bovine biologicals, but recovery of fastidious organisms is reduced by ~40 % compared to authentic rumen-fluid M2GSC. Use only for non-critical applications.
Sodium-carbonate handling. Na2CO3 in Mixture B raises pH on dissolution; this is part of the buffer-balance design. Do not pre-dissolve and store the Na2CO3 aliquot in aqueous solution at room temperature — it will absorb CO2 from the atmosphere and convert to NaHCO3.
Cellobiose contamination check. Reagent-grade cellobiose can contain trace glucose. For studies requiring strict carbohydrate definition, use research-grade cellobiose with documented purity ≥ 99.5 %.
Rumen-fluid colour. Reconstituted rumen fluid is dark amber-brown. The final medium has a darker appearance than YCFA / mGAM — this is normal and does not indicate problems.
Bovine and ovine biosecurity. Both bovine (some rumen-fluid lots) and ovine (alternative rumen-fluid source) zoosanitary documentation is available. EU and Japan customs may require additional dossiers; documentation pack on request.

Storage and Expiry · Safety

  • Dehydrated Mixture A: 15–30 °C in original packaging. Shelf life 30 months.
  • Mixture B (cysteine + Na2CO3, N2-flushed): 4 °C in original sealed packaging. Shelf life 12 months sealed; use within 14 days of opening.
  • Lyophilised rumen-fluid concentrate: −20 °C protected from light. Shelf life 24 months unopened. Reconstituted rumen fluid: use within 48 h.
  • Stock H, Stock K, Stock S: as for GMM — 4 °C, light-protected.
  • Prepared broth, aerobic 4 °C: 2 weeks routine (rumen-fluid component is perishable).
  • Prepared broth, anaerobic (vacuum-sealed + O2 absorber): 8 weeks for strict-anaerobe culturomics use.

Safety notes. Rumen fluid is bovine / ovine biological material. Handle inside a Class II BSC during reconstitution. SCFAs are odorous; perform Stock S addition under controlled ventilation. SDS available on request.

References

  1. Hobson PN. (1969). Rumen bacteria. In: Methods in Microbiology, vol 3B. Academic Press, pp. 133–149. [Original M2 medium description]
  2. Miyazaki K, Martin JC, Marinsek-Logar R, Flint HJ. (1997). Degradation and utilization of xylans by the rumen anaerobe Prevotella bryantii. Anaerobe 3: 373–381. [M2 modification, SCFA addition]
  3. Browne HP, Forster SC, Anonye BO, Kumar N, Neville BA, Stares MD, Goulding D, Lawley TD. (2016). Culturing of 'unculturable' human microbiota reveals novel taxa and extensive sporulation. Nature 533: 543–546. [Modern human-gut adaptation of M2GSC]
  4. Lagier J-C et al. (2016). Culture of previously uncultured members of the human gut microbiota by culturomics. Nature Microbiology 1: 16203.
  5. Goodrich JK et al. (2014). Human genetics shape the gut microbiome. Cell 159: 789–799. [Christensenella minuta heritability and M2GSC cultivation]
  6. Rosero JA et al. (2016). Reclassification of Eubacterium rectale in the genus Agathobacter. IJSEM 66: 768–773.
  7. Shetty SA et al. (2018). Reclassification of Eubacterium hallii as Anaerobutyricum hallii. IJSEM 68: 3741–3746.
  8. Duncan SH et al. (2002). Acetate utilisation and butyryl coenzyme A (CoA): acetate-CoA transferase in butyrate-producing bacteria from the human large intestine. Appl Environ Microbiol 68: 5186–5190. [Cross-feeding rationale for SCFA mix]

Frequently Asked Questions

Q1. Why is rumen fluid critical to M2GSC?
Rumen fluid supplies undefined growth factors (complex fatty acids, branched-chain amino-acid derivatives, polyamines, and additional cofactors) that fastidious Firmicutes within Lachnospiraceae, Ruminococcaceae, and Christensenellaceae require for primary isolation. Defined-medium alternatives (no rumen fluid) give ~40 % lower recovery of these clades. For maximum-diversity culturomics — the application that justifies the medium's price — rumen fluid is non-negotiable.
Q2. How does M2GSC compare to YCFA Modified Medium for gut culturomics?
YCFA and M2GSC are complementary culturomics media. YCFA gives excellent recovery of SCFA-utilising butyrate producers (Faecalibacterium, Roseburia) and is the gold standard for that specific group. M2GSC matches YCFA on butyrate producers and adds substantial recovery of Lachnospiraceae sp. nov., Christensenellaceae, and the broader 'unculturable' long-tail (per Browne et al. 2016). For maximum-diversity culturomics, run both YCFA and M2GSC in parallel — together they cover > 80 % of 16S-detected human gut taxa.
Q3. Can M2GSC be prepared without rumen fluid?
The defined-medium variant is available as an R&D-grade alternative (custom order), substituting rumen fluid with a complex vitamin / micronutrient / undefined-cofactor pack. Recovery of fastidious organisms drops by ~40 %; this is acceptable for non-critical applications (e.g., screening pure-culture growth conditions) but not for maximum-diversity culturomics.
Q4. Why is the pH set to 6.8 rather than 7.0–7.4 as for other anaerobic media?
M2GSC pH 6.8 reflects rumen-fluid physiology and favours acidotolerant Firmicutes. The pH is set deliberately lower than YCFA (7.2) and mGAM (7.3). Adjusting to higher pH → suboptimal recovery of the rumen-derived organisms and the acidotolerant human-gut Firmicutes the medium is designed to recover.
Q5. Can M2GSC be used for non-gut anaerobic culture (clinical, environmental)?
It can, but the medium is not optimised for these uses. For clinical anaerobic isolation, BHI-S, Wilkins-Chalgren, or Modified Chopped Meat Broth are more cost-effective. M2GSC's commercial premium is specifically for gut culturomics and rumen microbiology.
Q6. How does the medium handle spore-forming organisms?
Browne et al. (2016) demonstrated extensive sporulation in M2GSC and used the medium for ethanol-shock-resistant spore-fraction culturomics. To enrich for spores, heat-treat the inoculum (60 °C × 30 min or ethanol 70 % × 15 min) before inoculation into pre-reduced M2GSC tubes. Clostridium, Anaerostipes, and other spore-formers germinate readily from this treatment.
Q7. What is the shelf life and stability of the lyophilised rumen-fluid concentrate?
Lyophilised rumen-fluid concentrate stored at −20 °C in light-protected packaging: 24 months unopened. After reconstitution: use within 48 h at 4 °C. Avoid freeze-thaw cycling of reconstituted material. The lyophilisation removes ~95 % of the original water content; rehydration recovers ~90 % of the original biological activity (validated by Browne-2016-organism growth-curve comparison).
Q8. Is M2GSC compatible with the GMExpression Anaerobic Preparation Kit?
Yes. The APK Hungate-tube vacuum-deoxygenation workflow applies identically. The Browne 2016 protocol used Hungate-tube anaerobic culture and APK is its modern equivalent. For the highest-fidelity reproduction of the Browne 2016 culturomics work, use APK-Plus (with palladium catalyst pellets) plus pre-reduction inside the AAE for 48 h before inoculation.