TG1 Escherichia coli Strains
Product Advantages: The fastest-growing cloning host derived from E. coli K-12 lineage, producing visible colonies on agar plates within just 7 hours at 37°C. As the primary strain for phage display applications, TG1 supports efficient M13 phage propagation and antibody library construction. The lacIqZΔM15 genotype enables blue/white screening for rapid clone identification. Ideal for high-throughput cloning, phage display library construction, plasmid amplification, and general molecular biology workflows requiring rapid colony growth. | Technical Parameters: Detection Range: N/A (cloning/host strain) | Sensitivity: High transformation efficiency with F' episome-mediated conjugation | Applications: Phage display (M13 filamentous phage), blue/white screening, plasmid cloning and amplification, recombinant DNA construction, and high-throughput molecular biology.
Product Overview: The TG1 strain is a derivative of the E. coli K-12 strain and is currently recognized as one of the fastest-growing cloning strains available. On LB agar plates at 37°C, visible colonies appear within approximately 7 hours — significantly faster than most standard laboratory strains. TG1 serves as the primary host strain for phage display applications, particularly with M13 filamentous phage systems used in antibody engineering and peptide library screening. It is also fully compatible with routine plasmid construction workflows. The presence of the lacIqZΔM15 allele enables blue/white colony screening via α-complementation of β-galactosidase. Notably, this strain does not carry the endA1 mutation, meaning intracellular nuclease levels are relatively high; therefore, when extracting plasmids from TG1 cultures, it is strongly recommended to use a protein-removal reagent (such as the neutralization buffer component of alkaline lysis kits) to effectively remove abundant nucleases that could degrade plasmid DNA.
Pricing & Availability
| Catalog No. |
Packing |
Storage |
Lot No. |
Expiry Date |
| S0026 |
100 µL |
-80°C |
According to label |
According to label |
Technical Specifications
| Genotype | K12 (lac-pro), supE, thi, hsdS / F'[traD36, proAB, lacIq, lacZΔM15] |
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| Resistance | None (antibiotic-sensitive) |
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| Strain Category | Escherichia coli K-12 derivative |
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| Culture Medium | LB Medium (no antibiotic) |
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| Culture Conditions | 37°C, aerobic |
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| Preservation Method | 20% glycerol, -80°C (or -20°C for short-term) |
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| Colony Appearance Time | ~7 hours at 37°C on LB plates |
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| Key Features | F' episome (traD36), lacIqZΔM15 (blue/white screening), supE (amber suppressor), fastest growth rate among K-12 clones |
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| Primary Applications | Phage display (M13), plasmid cloning, blue/white screening, general molecular biology |
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Strain Description & Characteristics
The TG1 strain is derived from the E. coli K-12 lineage and represents one of the fastest-growing cloning hosts available in modern molecular biology laboratories. Its key characteristics include:
Strain Features
- Rapid Growth Rate: Among all K-12-derived cloning strains, TG1 exhibits the fastest growth velocity. Visible colonies appear on LB agar plates after only ~7 hours of incubation at 37°C, making it ideal for time-sensitive cloning workflows and high-throughput applications where rapid colony formation is critical.
- Phage Display Host: TG1 is the primary and most widely used host strain for M13 filamentous phage display systems. The F' episome carrying traD36 enables efficient F-pilus formation, which is essential for M13 phage infection and propagation. This makes TG indispensable for antibody library construction, affinity maturation, and peptide display screening.
- Blue/White Screening Compatible: The lacIqZΔM15 genotype on the F' episome provides both the lac repressor (lacIq, overexpressed for tight regulation) and the ω-fragment of β-galactosidase (lacZΔM15). When combined with plasmids carrying the α-fragment (such as pUC series or pBluescript vectors), functional β-galactosidase is reconstituted through α-complementation, enabling blue/white colony screening on X-gal/IPTG plates.
- supE Suppressor: The supE (supE44) amber suppressor tRNA allows readthrough of amber (UAG) stop codons, which can be useful for certain phage display applications where partial readthrough is desired.
- Note on Plasmid Extraction: Unlike many modern cloning strains (e.g., DH5α, TOP10), TG1 does not carry the endA1 mutation. This means intracellular endonuclease I activity remains high. For optimal plasmid yield and quality, always use a plasmid miniprep kit with effective protein/nuclease removal steps (particularly the neutralization buffer in alkaline lysis protocols) when preparing plasmid DNA from TG1 cultures.
TG1 must be cultured in antibiotic-free LB medium under aerobic conditions at 37°C. For long-term storage, prepare 20% glycerol stocks and store at -80°C (or -20°C for short-term storage up to several months).
Storage & Propagation Guidelines
Storage
Glycerol stocks should be stored at -80°C (preferred) or -20°C (acceptable for short-term). Before freezing, aliquot the stock into multiple small volumes to minimize repeated freeze-thaw cycles, which progressively reduce cell viability.
Propagation Methods
Two methods are recommended for expanding TG1 from glycerol stocks:
- Direct Inoculation: Pipette 100–200 µL of glycerol stock directly into 3–5 mL of fresh LB medium (no antibiotic). Incubate overnight at 37°C with shaking (220 rpm).
- Plate Streaking Method: Streak the glycerol stock onto an LB agar plate (no antibiotic) using the cross-streak method. Incubate at 37°C for 7 hours (or overnight). Pick a single well-isolated colony and inoculate into fresh LB medium for overnight culture.
Minimal Medium Plate Preparation
For specialized applications requiring defined minimal media, prepare as follows:
Autoclave the salt base and agar base bottles simultaneously. Cool both to 50–60°C, then combine. Add 1 mL of 1 M MgCl₂·6H₂O, 1 mL of 1 M CaCl₂·2H₂O, 1 mL of 1 M thiamine HCl, and 5 mL of 20% glucose. Mix thoroughly and pour plates immediately.
Caution & Storage Guidelines
- 1. This product is FOR RESEARCH USE ONLY!
- 2. Upon receiving the second-generation glycerol stock, it should be immediately stored at -80°C and should NOT be stored at -20°C for long-term preservation.
- 3. Minimize freeze-thaw cycles of the glycerol stock — the more cycles, the lower the strain viability. Aliquot before initial freezing whenever possible.
- 4. When propagating the strain, ensure no more than four generations per expansion to maintain genomic stability. After propagation, re-preserved strains must undergo phenotypic and functional validation. Only strains with fully intact phenotypes and functions may be used as seed stocks.
Frequently Asked Questions (FAQ)
Q: Why is TG1 considered the preferred strain for phage display applications?
A: TG1 carries three genetic features that make it uniquely suited for M13 phage display: (1) The F' episome with traD36 enables expression of the F-pilus, which is absolutely required for M13 bacteriophage infection — without the F' factor, M13 cannot efficiently infect the host cells; (2) The supE amber suppressor allows controlled readthrough of amber stop codons, which is essential for displaying certain peptide/protein libraries where the displayed fusion protein contains an amber codon; (3) The extremely rapid growth rate (~7-hour colonies at 37°C) dramatically accelerates the phage display workflow cycle, from transformation to panning output. These combined features have established TG1 as the gold-standard host for antibody phage display libraries since the technology's inception.
Q: How do I handle the high nuclease issue when extracting plasmids from TG1?
A: Unlike DH5α and most modern cloning strains, TG1 lacks the endA1 mutation. Endonuclease I (EndA) is a periplasmic enzyme that degrades double-stranded DNA. During alkaline lysis plasmid preparation, if cells are inadequately lysed or the neutralization step is incomplete, EndA can contaminate the final plasmid prep and subsequently degrade your plasmid DNA during downstream applications (especially restriction digests and sequencing). To mitigate this: (1) Always use a commercial plasmid miniprep kit with optimized neutralization buffer that effectively precipitates proteins and nucleases; (2) Ensure complete resuspension, lysis, and neutralization with thorough mixing at each step; (3) Consider an additional RNase A treatment step if RNA contamination is suspected; (4) For large-scale preps, perform an additional phenol-chloroform extraction or use a column-based cleanup step. If you consistently need high-quality plasmid from TG1, consider switching to an endA1-deficient strain like DH5α for routine cloning while reserving TG1 specifically for phage display work.
Q: What is the difference between TG1's F' episome and a regular F-plasmid, and why does it matter?
A: The F' episome carried by TG1 is a modified Fertility (F) factor — a conjugative plasmid that enables bacterial mating. Specifically, TG1's F' factor is F'[traD36, proAB, lacIq, lacZΔM15], which differs from a wild-type F-plasmid in three important ways:
• traD36 mutation: This partially disables the transfer (tra) operon, meaning the F' factor can still express the genes needed for F-pilus formation (essential for M13 infection) but has greatly reduced ability to transfer itself to other bacteria by conjugation — improving biosafety in the laboratory.
• proAB insertion: The proline biosynthesis genes are inserted into the F' factor, complementing the chromosomal lac-pro deletion in the K-12 background.
• lacIqZΔM15 insertion: This provides both the overexpressed Lac repressor (for tight control of lac promoter-driven vectors) and the ω-fragment of β-galactosidase (for α-complementation blue/white screening).
The F' episome is maintained as an extrachromosomal element and is stably inherited by daughter cells. It is what makes TG1 simultaneously suitable for phage display (via F-pilus), blue/white screening (via lacZΔM15), and complementation of the chromosomal proline auxotrophy (via proAB).
Citations & References
(Editor's Note: Please update the citations below to reflect relevant literature.)
- [1] Gibson, T.J. (1984). Studies on the Epstein-Barr virus genome. Ph.D. thesis, University of Cambridge. (TG1 strain origin and characterization.)
- [2] Sidhu, S.S., et al. (2003). Phage display for selection of novel binding peptides. Methods in Enzymology, 363, 212–234.
- [3] Sambrook, J., & Russell, D.W. (2001). Molecular Cloning: A Laboratory Manual, 3rd ed. Cold Spring Harbor Laboratory Press. (Chapter 1: Media preparation and bacterial culture.)
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