SOS-ChromoTest™ Kit
A rapid microplate genotoxicity bioassay using a genetically engineered strain of E. coli PQ37 to detect DNA damage in water, wastewater, effluents, chemicals, and environmental samples — providing clear, objective results in just a few hours.
The SOS-ChromoTest™ is based on a novel genetically engineered strain of Escherichia coli PQ37, in which the sfiA SOS repair gene is fused to the lacZ reporter gene. When a genotoxic agent causes DNA damage, the SOS repair pathway is activated, triggering simultaneous production of β-galactosidase. The degree of enzyme induction — measured by a simple colour change — is directly proportional to the extent of DNA damage and is expressed as the SOS-Inducing Potency (SOSIP). Results are highly correlated with the Salmonella Ames Test for many classes of genotoxic compounds.
- Test organismEscherichia coli PQ37 (sfiA::lacZ chromosomal fusion)
- EndpointSOS DNA repair induction — β-galactosidase activity; darker colour = more genotoxic; clear wells = acute cytotoxicity
- Result expressionSOS-Inducing Potency (SOSIP); induction factor (IF)
- Incubation time2 hours (+ substrate development)
- Format96-well microplate
- Tests per kit96 unit tests total (min. 16 for standards & controls; 4–10 samples per kit)
- Metabolic activationCompatible with S9 liver fraction (Product No. 5051S9) for pro-mutagen testing
- DetectionVisual or spectrophotometric at 420 nm / 580 nm; substrates: X-gal alone (blue) or X-gal + pNPP simultaneously (green)
- Sample matricesWater, wastewater, effluents, sediment extracts, chemicals, food, cosmetics, air extracts
- Ames correlationHighly correlated with Salmonella Ames Test; fewer false positives
🛒 Order or Enquire
🍁 Ships from Burlington, Ontario, Canada · International shipping available · Cold-chain packaging included
How the SOS-ChromoTest™ Works
When a genotoxic compound enters an E. coli PQ37 cell and damages DNA, the cell activates the SOS repair system. In the SOS-ChromoTest™ strain, the sfiA SOS repair gene is genetically fused to the lacZ gene encoding β-galactosidase. SOS induction therefore causes β-galactosidase to be produced simultaneously — its activity is measured by adding chromogenic substrates (X-gal alone, or X-gal + pNPP together) and reading the resulting colour. The darker the colour, the more genotoxic the sample — the bacteria are working harder to repair damaged DNA. The greater the DNA damage, the stronger the enzyme induction and the deeper the colour development.
ProcedureSimple 4-Step Assay Procedure
Expose
Add sample dilutions to E. coli PQ37 bacteria in microplate wells; incubate 2 hours at 37°C
Develop
Add chromogenic substrates: X-gal alone (blue endpoint) or X-gal + pNPP simultaneously (green endpoint); incubate to allow colour development
Read
Measure absorbance at 420 nm (β-galactosidase) and 580 nm (cell density) or evaluate visually
Calculate SOSIP
Calculate the SOS-Inducing Potency (SOSIP) or induction factor (IF) relative to positive and negative controls
Fig. 1 — SOS-ChromoTest™ 96-Well Plate Result
The photograph below shows a typical SOS-ChromoTest™ result. The assay uses two chromogenic substrates simultaneously: X-gal alone produces a blue colour, while X-gal combined with pNPP produces a green colour. In both cases, the intensity of colour is directly proportional to genotoxicity — the darker the colour, the harder the bacteria are working to repair damaged DNA, and therefore the more genotoxic the sample. Clear / colourless wells indicate acute cytotoxicity rather than genotoxicity — the bacteria have been killed before DNA repair can be measured. As sample dilutions increase across the plate (lower concentration), colour intensity decreases, reflecting the dose–response relationship.
Reading the Plate Result
Clear / Colourless
Acute cytotoxicity. The bacteria have been killed by the sample before any DNA repair activity can occur. No β-galactosidase is produced. Genotoxicity cannot be assessed in these wells — the sample concentration is too high.
Blue — X-gal Substrate Only
β-galactosidase activity detected using X-gal alone. The darker the blue, the more the bacteria are attempting to repair DNA damage — and therefore the more genotoxic the sample. Blue colour fades with increasing dilution as genotoxic load decreases.
Green — X-gal + pNPP Simultaneously
β-galactosidase activity detected using X-gal and pNPP together. Again, the darker the green, the harder the bacteria are working to fix damaged DNA — the more genotoxic the sample. Green intensity decreases across the dilution series.
Genotoxicity Screening for Drinking Water & Wastewater
The SOS-ChromoTest™ is widely used in drinking water and wastewater research and monitoring programs. EBPI has supported international universities and environmental agencies in the application of the SOS-ChromoTest™ to water quality assessment for over 10 years.
💧 Drinking Water & Source Water
Disinfection by-products (DBPs) such as trihalomethanes, haloacetic acids, and chloramines formed during water treatment can have genotoxic activity. The SOS-ChromoTest™ provides a rapid, cost-effective screen for genotoxic potential in:
- Treated drinking water and distribution system samples
- Source water and reservoir monitoring
- Disinfection by-product assessment
- Groundwater contamination screening
- Source Water Protection Plan (SWPP) investigations
See also: Microbial Source Tracking for fecal contamination source identification in drinking water catchments.
🏭 Wastewater & Effluent Monitoring
Industrial and municipal effluents may contain complex mixtures of genotoxic compounds including PAHs, heavy metals, pharmaceuticals, and industrial chemicals. The SOS-ChromoTest™ screens for:
- Industrial effluent genotoxicity before discharge
- Municipal wastewater treatment plant (WWTP) influent and effluent
- Pharmaceutical and hospital wastewater
- Mining and leachate effluents
- Combined sewer overflow (CSO) events
- Treated effluent compliance screening
Complement with the Toxi-ChromoTest™ for a combined acute toxicity + genotoxicity battery on the same effluent sample.
⚙️ Metabolic Activation with S9 Fraction (Product No. 5051S9)
Many genotoxic compounds (pro-mutagens) require metabolic activation before they become genotoxically active — they are not intrinsically genotoxic but are converted to active forms by liver enzymes. The SOS-ChromoTest™ can be run with or without S9 metabolic activation. Adding S9 (a crude rat liver enzyme fraction) to the assay allows detection of pro-mutagens such as benzo[a]pyrene, aflatoxin B1, and aromatic amines. EBPI’s S9 Activation Enzymes (Product No. 5051S9) are available separately and are optimized for use with the SOS-ChromoTest™.
Full Range of SOS-ChromoTest™ Applications
Environmental Water Monitoring
Drinking water, groundwater, surface water, and sediment pore water genotoxicity screening.
Industrial & Municipal Effluents
Effluent characterization, compliance testing, and pre/post-treatment genotoxicity evaluation.
Chemicals & Raw Materials
Rapid genotoxicity screening of industrial chemicals, process intermediates, and raw materials.
Food & Cosmetics
Genotoxicity screening of food additives, packaging extracts, cosmetic ingredients, and formulations.
Sediment & Soil Extracts
Aqueous extracts of sediment and soil assessed for genotoxic PAHs, heavy metals, and persistent contaminants. See also: SOS Direct Contact Sediment Test (Product No. 7031).
Research & Education
Used in universities across North America. Available in educational kit format — contact EBPI for educational pricing and protocols.
Kit Specifications & Performance Characteristics
| Parameter | Detail |
|---|---|
| Product Number | 5031 |
| Product Name | SOS-ChromoTest™ |
| Test Organism | Escherichia coli PQ37 (chromosomal sfiA::lacZ fusion; rfa mutation for increased membrane permeability) |
| Assay Endpoint | SOS DNA repair induction; β-galactosidase enzyme activity. Darker colour = more genotoxic (bacteria working harder to repair DNA damage). Clear wells = acute cytotoxicity (bacteria killed before repair can occur) |
| Substrate System | X-gal alone (produces blue colour) or X-gal + pNPP simultaneously (produces green colour). Colour intensity decreases with increasing sample dilution |
| Result Expression | SOS-Inducing Potency (SOSIP); Induction Factor (IF); dose–response relationship |
| Test Format | 96-well microplate |
| Incubation Time | 2 hours at 37°C (+ substrate development period) |
| Tests per Kit | 96 unit tests total (minimum 16 for standards & controls; 4–10 samples per kit with dilutions) |
| Detection Method | Spectrophotometric at 420 nm (β-galactosidase) and 580 nm (turbidity correction), or visual qualitative evaluation |
| Metabolic Activation | Compatible with S9 fraction (available separately as Product No. 5051S9) for pro-mutagen testing |
| Sample Matrices | Water, wastewater, effluents, sediment and soil extracts, air extracts, chemicals, food, cosmetics, and any material soluble in aqueous micro-suspension |
| Ames Test Correlation | Highly correlated with Salmonella Ames Test for many compound classes; fewer false positives reported |
| Kit Contents | All reagents and disposable plastics for a minimum of four complete sample sets (including dilutions and controls) |
| Manufacturer | EBPI — Environmental Bio-Detection Products Inc., Burlington ON, Canada |
Technical Resources
Excel Worksheet
Data recording and SOSIP calculation worksheet for the SOS-ChromoTest™
⬇️ Download PDFAssay Flow Chart
Quick-reference bench flowchart for the SOS-ChromoTest™ procedure
⬇️ Download PDFOther Genotoxicity & Toxicity Testing Kits
Contact EBPI for pricing, volume discounts, educational kit options, or technical support for the SOS-ChromoTest™.