Overview

2×YT Broth (Double Yeast-Tryptone) is the high-density variant of LB designed for high-titre filamentous-phage stock production and large-scale recombinant work. First described by Miller (1972) in Experiments in Molecular Genetics and codified in Sambrook & Russell (2001), 2×YT carries 60 % more tryptone and 2× the yeast extract of LB at the same NaCl strength. The defining feature is sustained E. coli growth to OD600 3–6 (vs ~2 for LB) before stationary-phase plateau, which directly drives a 10–100× higher M13 supernatant titre and a 5–10× higher λ lysate titre.

The GMExpression formulation is supplied as pre-weighed dehydrated base (Tryptone 16 g/L, yeast extract 10 g/L, NaCl 5 g/L; total 31 g/L) with pre-balanced pH 7.0 ± 0.2. Optional sterile-filtered antibiotic stocks (kanamycin for M13K07 / VCSM13 helper-phage selection, ampicillin or carbenicillin for phagemid selection) and MgSO4 (for λ tail-attachment supplementation) are supplied as post-autoclave additions. 2×YT is the broth-of-record for phage-display library biopanning across the antibody-, peptide-, and scaffold-engineering literature.

We also have

LB Broth (Lennox / Miller) · NZCYM Broth (lambda gold-standard) · Bacteriophage Nutrient Broth (ΦX174 propagation grade) · TSB + 10 % Glycerol (host cryostock) · SM Buffer (phage diluent / storage) · BHI Broth (Gram-positive phage hosts)

Package Contents

Each GMExpression 2×YT kit contains:

  • Mixture A — pre-weighed dehydrated 2×YT base (Tryptone 80 g, yeast extract 50 g, NaCl 25 g; total 155 g for 5 L final volume). Triple-foil-pouched; CofA traceable to the peptone and yeast-extract lots.
  • Stock B (optional) — 50 mg/mL kanamycin sulfate, filter-sterilised at 0.22 µm, sterile-fill 5 mL amber vial; dosed at 1 mL/L for 50 µg/mL final (M13K07 / VCSM13 helper-phage selection).
  • Stock C (optional) — 100 mg/mL ampicillin or carbenicillin sodium, filter-sterilised, sterile-fill 5 mL vial; dosed at 1 mL/L for 100 µg/mL final (phagemid selection).
  • Stock D (optional) — 1 M MgSO4 · 7H2O, filter-sterilised, sterile-fill 10 mL vial; dosed at 10 mL/L for 10 mM Mg2+ λ-tail-attachment supplementation.
  • Instruction manual including M13 helper-phage propagation, phage-display biopanning round protocol, PEG-precipitation phage harvest method, and a recombinant-protein expression annex (A5 booklet, v1.0).

Customisation options on request: animal-origin-free 2×YT (soy-substituted peptone), low-endotoxin 2×YT for clinical-grade phage display, antifoam-supplemented 2×YT for fermenter use, IPTG-supplemented 2×YT for induction workflows.

Composition — per 1 L equivalent unless stated otherwise

2×YT Broth (Miller 1972 / Sambrook & Russell 2001 / BD Difco 244020; per 1 L)

ComponentConcentrationFunction
Tryptone (pancreatic digest of casein)16.0 gPrimary nitrogen and free amino acid source; 60 % more than LB — supports OD600 3–6
Yeast extract10.0 gB-vitamins, purines, pyrimidines, NAD precursors; 2× the LB load — directly drives higher burst size and recombinant protein yield
Sodium chloride (NaCl)5.0 gOsmotic balance (86 mM); maintained at LB-Lennox level to preserve phage adsorption rates

Total dry solids: 31 g/L. Pre-autoclaving pH: 7.0 ± 0.2 at 25 °C — typically requires ~ 0.2 mL of 5 M NaOH per litre to reach pH 7.0 (the higher peptone content shifts the equilibrium slightly acidic).

Optional supplements for phage / phage-display / expression workflows

SupplementFinal concentrationUse caseNotes
Kanamycin sulfate (CAS 25389-94-0)50 µg/mLM13K07, VCSM13 helper phage selectionAdd 1 mL of 50 mg/mL stock per litre post-autoclave; stable in 2×YT at 37 °C for 24–48 h
Ampicillin or carbenicillin sodium100 µg/mLPhagemid selection (pComb, pIT2, pAK / pYK series)Add 1 mL of 100 mg/mL stock per litre post-autoclave; carbenicillin is more stable than ampicillin in 37 °C cultures
Chloramphenicol25–35 µg/mLDual-selection with pComb / pAK vectorsAdd 1 mL of 25 mg/mL ethanolic stock per litre
MgSO4 · 7H2O10 mM (= 2.47 g/L)λ phage lysate at 2×YT yieldsAdd 10 mL of 1 M sterile filtrate per litre post-autoclave
IPTG (Isopropyl β-D-thiogalactopyranoside)0.1–1.0 mMLac-operator induction (BL21(DE3), Rosetta etc.)Add when culture reaches OD600 0.4–0.8; do not pre-induce
Glucose1–2 % w/v (= 10–20 g/L)"2YTAG" for phage-display amplificationCatabolite-represses helper-phage promoter; standard phagemid round-amplification format

→Culturomics and Media Navigator

Need help matching this medium to your phage–host combination — or starting from a phage-display vector 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 supported phage–host pairings, or (ii) start from a phagemid / helper-phage / display vector and view the panel of GMExpression media for biopanning, amplification, and titering. The Navigator integrates 2×YT with the wider LB, NZCYM, Bacteriophage Nutrient Broth, BHI, SM Buffer, TSB–Glycerol, PPLO, Hayflick, and SP-4 catalogue.

Use and Applications

  • M13 / fd / f1 filamentous-phage stock production. 2×YT + Kan 50 µg/mL inoculated with M13K07 or VCSM13 helper phage + F+ E. coli (TG1, JM109, ER2738, XL1-Blue); shake overnight 30 or 37 °C, 250 rpm; PEG-precipitate the supernatant to harvest the phage. Typical titre 1012–1013 PFU/mL — an order of magnitude above LB.
  • Phage-display library biopanning rounds. 2×YT + Amp/Carb + Kan + glucose ("2YTAG") for round amplification; 2×YT + Amp/Carb alone for the helper-phage rescue step. Standard Smith / Winter / Marks / Bradbury protocols.
  • λ phage liquid lysate. 2×YT + 10 mM MgSO4 + λ at MOI 0.01; harvest at clearing; expect > 1010 PFU/mL. NZCYM remains the gold standard but 2×YT is a routine alternative.
  • Recombinant protein expression. Routine high-density growth broth for BL21(DE3), Rosetta, NiCo21, C41/C43, and Origami strains under IPTG induction; final OD600 4–6 in shake flasks, 8–12 in stirred bioreactors with antifoam.
  • Plasmid maxiprep host growth. Single-colony inoculation of 2×YT + selection antibiotic; overnight to OD600 4–5 gives 2–3× the wet-cell mass of an equivalent LB culture, enabling proportionally larger plasmid yields per litre.
  • Single-stranded DNA template preparation for Sanger sequencing or site-directed mutagenesis using M13mp / pBluescript / pCAB phagemids.
  • Helper-phage propagation for M13K07 and VCSM13 (both carry a kanamycin-resistance cassette; the helper-phage–infected cells are selected on kanamycin).

Compatible Microorganisms

Phage-display and filamentous-phage hosts (primary use)

  • E. coli TG1 (F+, supE, hsdD5, thi) — antibody scFv / Fab phage-display reference host (Cambridge Antibody Technology / MRC LMB heritage)
  • E. coli ER2738 (F+) — New England Biolabs PhD-series peptide display host
  • E. coli JM109 (F+) — M13 propagation and ssDNA preparation
  • E. coli XL1-Blue (F+, tetR) — Agilent phagemid host
  • E. coli SS320 (F+, electroporation-optimised) — large phage-display library electroporation

Recombinant protein expression hosts

  • E. coli BL21(DE3), BL21-Star, BL21-CodonPlus — T7 promoter-driven expression
  • E. coli Rosetta(DE3), Rosetta2(DE3) — rare-codon supplementation
  • E. coli Origami(DE3), SHuffle — disulfide-bond-supportive expression
  • E. coli NiCo21(DE3) — metal-affinity-optimised expression
  • E. coli C41(DE3), C43(DE3) — membrane-protein and toxic-protein expression

General molecular biology hosts

  • Cloning strains: DH5α, TOP10, NEB Stable, NEB 5-alpha
  • BAC / cosmid hosts: DH10B, EPI300

Not optimised for: ΦX174 (use LB Lennox + 5 mM CaCl2 with E. coli C; 2×YT is too rich), Gram-positive phages (use BHI), mycoplasmas (use PPLO + serum), strictly anaerobic phage hosts (use anaerobic-modified BHI).

Preparation

1Weigh. Use the pre-weighed Mixture A: 31 g for 1 L. Tare a clean autoclavable Schott bottle or flask of at least 1.5× final volume to leave headspace for foaming (2×YT foams more than LB during autoclaving).
2Suspend & dissolve. Add Mixture A to 950 mL of distilled or deionised water (Type II reagent water, > 1 MΩ·cm). Stir for 5–8 min; the higher peptone load requires a longer dissolution time than LB.
3Adjust pH. Check pH with a calibrated meter; target 7.0 ± 0.2 at 25 °C. The base typically reads pH 6.7–6.8 before adjustment; titrate with 5 M NaOH (typically 0.2–0.3 mL/L) to bring to pH 7.0.
4Bring to final volume. Make up to 1000 mL with distilled water.
5Dispense. Bulk flasks: leave caps one-quarter turn loose for pressure equilibration; do not fill flasks more than 40 % full when working with high-aeration shake cultures (the higher peptide content increases foaming).
6Autoclave. 121 °C × 15 min for ≤ 500 mL; 121 °C × 20 min for 1 L bottles. Slow cooling. Optional antifoam (0.01 % silicone-based) for fermenter-scale work.
7Cool to < 50 °C before adding post-autoclave supplements (antibiotics, Mg2+, IPTG, glucose).
8Add selection antibiotic. For M13K07 / VCSM13 helper-phage work: 1 mL of 50 mg/mL kanamycin per litre (= 50 µg/mL final). For phagemid selection: 1 mL of 100 mg/mL ampicillin or carbenicillin per litre. Mix gently.
9For λ lysate work. Add 10 mL of 1 M MgSO4 per litre (= 10 mM final); do not omit for λ — tail attachment to LamB requires > 2 mM Mg2+.
10Storage. Sealed glass bottles at 2–8 °C, light-protected. Use antibiotic-supplemented broth within 2 weeks (kanamycin), 1 week (carbenicillin), or 3–5 days (ampicillin).

Critical control points

  • F-pilus expression temperature. Filamentous phages adsorb to the F pilus, whose expression is temperature-regulated. Standard biopanning rounds are performed at 30 °C to maintain the F-pilus at maximum density; 37 °C reduces F-pilus density and lowers phage recovery. Helper-phage rescue is also typically done at 30 °C for the same reason. Plasmid maxiprep and recombinant protein expression are routinely done at 37 °C.
  • Glucose catabolite repression. The "2YTAG" format (2×YT + Amp + Glucose) deliberately includes 1–2 % glucose to keep the phagemid lac / lacUV5 promoter driving pIII-fusion expression under catabolite repression during phagemid round amplification, preventing premature pIII display, particle assembly, and pIII-toxicity-driven clone bias. When switching to the rescue step, the cells must be washed out of glucose-containing broth (and, if the phagemid promoter is IPTG-inducible, IPTG added) for full helper-phage rescue and particle release.
  • Antifoam compatibility with downstream phage work. Silicone antifoams are generally phage-inert; polypropylene-glycol-based antifoams (some Antifoam 204 formulations) can reduce filamentous-phage infectivity by 20–50 % per round. Verify antifoam compatibility before fermenter-scale display work.
  • Oxygen transfer rate. 2×YT cultures consume oxygen at 2–3× the rate of LB cultures at equivalent OD600. Shake flasks: 1:5 culture-to-flask ratio, 250 rpm minimum; fermenters: aeration ≥ 1 vvm or DO control ≥ 30 % saturation throughout the growth phase.

Cautions

Foaming during autoclaving and aeration. 2×YT contains 60 % more peptide than LB and foams vigorously during autoclaving and during shake-flask aeration. Use bottles / flasks at ≤ 40 % fill, cap one-quarter turn loose during autoclaving, and add silicone-based food-grade antifoam (e.g. Antifoam 204 or 289) at 0.01–0.05 % v/v for fermenter-scale batches. Confirm antifoam is compatible with downstream filamentous-phage display.
pH drift in dense cultures. Mixed-acid fermentation by E. coli at OD600 > 4 drops the pH from 7.0 toward 5.5–6.0 within 4–6 h. For extended expression runs or biopanning rounds use 50 mM MOPS pH 7.4 or 25 mM HEPES pH 7.4 as a buffer top-up; do not buffer with phosphate (incompatible with Mg2+ in λ work).
Ampicillin instability. Ampicillin has a half-life of ~ 6 h in 37 °C cultures; overnight cultures of phagemid-bearing hosts lose ampicillin selection by ~ 10 PM and may accumulate plasmid-free cells. Use carbenicillin (half-life ~ 24 h) for overnight cultures and dual-day biopanning rounds. The 2×YT formulation does not affect β-lactam stability per se — it is purely a function of incubation time and temperature.
Helper-phage rescue at 37 °C drops library diversity. Standard phage-display protocols rescue at 30 °C precisely to maintain F-pilus density and avoid clone-bias from F-pilus loss in fast-growing cells. Rescuing at 37 °C accelerates round throughput by ~ 30 % but documented protocols report 5–10× loss of library diversity per round. Use 30 °C for naive library rounds; 37 °C may be acceptable for late-round affinity-mature selections.
PEG precipitation conditions. Filamentous-phage harvest from 2×YT supernatant by 4 % PEG 8000 + 0.5 M NaCl on ice for 60 min is standard. Excessive PEG (> 5 %) co-precipitates host-cell proteins and reduces phage purity; insufficient PEG (< 3 %) gives a low-recovery pellet. Lower PEG concentration is preferable for naive libraries (preserves diversity); higher PEG (5 %) is used for affinity-matured selections where yield matters more than purity.

Storage and Expiry · Safety

  • Dehydrated powder (Mixture A): store sealed at 15–25 °C in original packaging away from direct sunlight. Shelf life 36 months from manufacture.
  • Sterilised broth (unsupplemented): 2–8 °C or 15–25 °C in sealed glass, 6 months; 1 month after opening.
  • Sterilised broth + kanamycin: 2–8 °C, 2 weeks.
  • Sterilised broth + ampicillin / carbenicillin: 2–8 °C, 1 week (ampicillin) or 2 weeks (carbenicillin).
  • 2×YT + MgSO4: 2–8 °C, 1 month (Mg2+ does not precipitate without phosphate).
  • Kanamycin 50 mg/mL stock: −20 °C aliquots, 12 months; 2–8 °C, 2 months.
  • Ampicillin 100 mg/mL stock: −20 °C aliquots, 6 months; 2–8 °C, 1 month.

Safety notes. 2×YT is a non-hazardous routine bacterial broth. The principal biosafety concerns are the host strain (most phage-display hosts are BSL-1) and the antibiotic stocks (kanamycin, ampicillin and carbenicillin are reproductive toxins on long-term occupational exposure; handle in PPE and follow institutional waste-stream rules). M13K07 and VCSM13 helper phages are non-pathogenic E. coli-specific viruses (BSL-1). SDS available on request.

References

  1. Miller, J. H. (1972). Experiments in Molecular Genetics. Cold Spring Harbor Laboratory Press. [Original 2×YT recipe]
  2. Sambrook, J. & Russell, D. W. (2001). Molecular Cloning: A Laboratory Manual, 3rd ed., CSH Press. Chapter 3 (Phage display) and Appendix A: 2×YT and M13 propagation protocols.
  3. Vieira, J. & Messing, J. (1987). Production of single-stranded plasmid DNA. Methods in Enzymology 153: 3–11.
  4. Smith, G. P. (1985). Filamentous fusion phage: novel expression vectors that display cloned antigens on the virion surface. Science 228: 1315–1317.
  5. Marks, J. D., Hoogenboom, H. R., Bonnert, T. P., McCafferty, J., Griffiths, A. D., Winter, G. (1991). By-passing immunization: human antibodies from V-gene libraries displayed on phage. Journal of Molecular Biology 222: 581–597.
  6. Barbas, C. F., Burton, D. R., Scott, J. K., Silverman, G. J. (2001). Phage Display: A Laboratory Manual. Cold Spring Harbor Press.
  7. BD Difco & BBL Manual, 12th ed., 2×YT Broth monograph (BD 244020).
  8. Russel, M., Lowman, H. B., Clackson, T. (2004). Introduction to phage biology and phage display. In Clackson & Lowman (eds), Phage Display, IRL/Oxford University Press.
  9. Rondot, S., Koch, J., Breitling, F., Dübel, S. (2001). A helper phage to improve single-chain antibody presentation in phage display. Nature Biotechnology 19: 75–78. [Hyperphage]
  10. Hanahan, D. (1983). Studies on transformation of Escherichia coli with plasmids. Journal of Molecular Biology 166: 557–580. [SOB / SOC origin]

Frequently Asked Questions

Q1. Why use 2×YT instead of LB for M13 propagation?
2×YT supports E. coli growth to OD600 3–6 vs ~ 2 for LB, which directly drives a 10–100× higher M13 supernatant titre (1012–1013 PFU/mL vs ~ 1011/mL in LB). Filamentous phages are released continuously from infected cells during growth without lysis, so total phage output is approximately linear in total host biomass × growth duration. The extra 60 % tryptone and 2× yeast extract pay for themselves in phage yield on every M13 stock preparation, every helper-phage propagation, and every biopanning round.
Q2. Can I use 2×YT for ΦX174 propagation?
Technically yes, but not recommended. ΦX174 burst size is essentially independent of broth richness above ~ 108 CFU/mL host density; once the host hits log phase the burst is determined by Ca2+ availability and LPS-receptor density, not by additional carbon/nitrogen. LB Lennox + 5 mM CaCl2 with E. coli C is the standard. For ASTM E1052 / PDA TR41 / regulatory-grade ΦX174 work, use Bacteriophage Nutrient Broth (the dedicated ΦX174-propagation grade) rather than 2×YT.
Q3. Why 30 °C for phage-display biopanning rounds?
F-pilus expression in E. coli is temperature-regulated by the traJ/traY control circuit, with maximum F-pilus density at 25–30 °C and minimum at 37 °C. Filamentous phages (M13, fd, f1) adsorb to the F-pilus tip, so the receptor density at 30 °C is > 3× that at 37 °C. Standard naive-library biopanning is therefore performed at 30 °C to maximise both adsorption efficiency and helper-phage rescue yield. 37 °C is acceptable for late-round affinity-mature selections where throughput matters more than diversity.
Q4. What is "2YTAG" and when should I use it?
2YTAG = 2×YT + Ampicillin 100 µg/mL + Glucose 2 % w/v. Standard phage-display round-amplification broth. Glucose catabolite-represses the phagemid lac (or lacUV5) promoter that drives pIII-fusion expression, keeping the displayed protein at a minimum during amplification and preventing premature phage-particle assembly and pIII-toxicity-driven clone bias. After the amplification step, cells are pelleted, washed out of glucose-containing broth, and resuspended in 2×YT + Amp + Kan (no glucose, optionally with IPTG) for the helper-phage rescue and phage particle release. Skipping the glucose step gives a 2–5× lower phage particle yield with clone bias toward fast-replicating, low-display variants.
Q5. How does the choice of helper phage (M13K07 vs VCSM13 vs hyperphage) affect my workflow?
M13K07 (Vieira & Messing 1987) carries the Tn903-derived kanamycin-resistance cassette and the p15A replication origin inserted into the M13 intergenic (IG) region between gene II and gene IV; produces wild-type-rate phage release on infection of an F+ host. VCSM13 (Stratagene/Agilent) is also kanamycin-resistant and functionally similar; some users prefer its slightly higher titre. Hyperphage (Rondot et al. 2001; M13K07-derived) carries a deletion in gene III, so the only pIII source is the phagemid-encoded pIII fusion — this increases display valency from ~ 0.1 to ~ 3–5 pIII-fusions per particle and is useful for low-affinity selections. Use M13K07 / VCSM13 for routine selections; hyperphage when target affinity is low and avidity matters.
Q6. Can I use 2×YT for IPTG-induced expression of T7-driven constructs in BL21(DE3)?
Yes — this is one of the standard recommended uses. 2×YT supports growth to OD600 0.6–0.8 typically within 3–4 h at 37 °C; induce at OD600 0.4–0.6 with 0.1–1.0 mM IPTG; harvest at 4–6 h post-induction. Compared to LB, 2×YT typically gives 2–3× the wet-cell mass and proportionally higher protein yield. For toxic proteins use C41(DE3) or C43(DE3); for low-temperature induction use 18 °C overnight (Studier auto-induction is also compatible with 2×YT, with added 0.5 % glycerol, 0.05 % glucose, 0.2 % α-lactose).
Q7. Why does my 2×YT broth read pH 6.7 before adjustment?
The higher peptide content of 2×YT shifts the buffer equilibrium slightly acidic. The tryptone component contains free aspartate, glutamate, and free amino acids with carboxylic side chains; at 16 g/L tryptone (vs 10 g/L in LB) the additional carboxylate load drops the unadjusted pH from ~ 7.1 in LB to ~ 6.7–6.8 in 2×YT. Titrating with 5 M NaOH (typically 0.2–0.3 mL/L) brings to pH 7.0 with no impact on growth or downstream applications. The CofA reports the pre- and post-adjustment pH for traceability.
Q8. Is 2×YT compatible with Studier auto-induction protocols?
Yes. 2×YT is the standard base for Studier ZYM-5052 auto-induction medium (Studier 2005, Protein Expr Purif 41: 207): 2×YT base + 25 mM Na2HPO4 + 25 mM KH2PO4 + 50 mM NH4Cl + 5 mM Na2SO4 + 2 mM MgSO4 + 1× trace metals + 0.5 % glycerol + 0.05 % glucose + 0.2 % α-lactose. The phosphate buffer prevents pH drift during overnight induction at 18–25 °C; the glucose / lactose / glycerol mixture provides auto-induction without manual IPTG addition. GMExpression can supply a ZYM-5052 add-on pack on request.