Genetically modified organisms (GMOs) are engineered with the goal of producing traits such as herbicide resistance, insect resistance or increased yield. GM crops are primarily grown for use in biofuels, animal feed and clothing; a relatively small percentage of total GMO production is used in food.
In the European Union, regulation of GMOs is based on thresholds for GMO content. The legal threshold for GMO content in food and feed in the EU is 0.9 percent; GMO content below that threshold is excluded from EU labeling requirements (1) . There is no law in the US requiring that foods with GMO ingredients be labeled accordingly; federal legislation has been proposed that would mandate labeling of any food with a GMO ingredient, but this proposed legislation has not advanced (2) .
Quantitative PCR assays are used to determine the amount of a GMO present in a food sample, enabling the verification of GMO thresholds; these quantitative assays are a relatively recent development in the food testing market. PCR-based GMO detection methods can be designed to detect a specific GMO event, or to detect a variety of different GMO events.
Event-specific GMO tests: A GMO “event” refers to a unique genetic alteration used to generate a specific transgenic plant. Event-specific assays are customized to detect specific genetic alterations in individual plants and crops.
Broad-spectrum GMO tests: Many transgenic sequences incorporate the same viral and bacterial genetic elements, to regulate expression of the genetic alterations. Testing for these elements does not reveal a specific GMO event; rather, these broad-spectrum tests can be used to detect a variety of different GMO events. Commonly used transgenic elements include:
- Bt endotoxin sequences: The engineered gene produces an endotoxin protein from the bacterium Bacillus thuringiensis, which is poisonous to certain insect pests. Organic growers commonly use Bt corn as an alternative to spraying insecticides.
- 35S promoter (P35S) from cauliflower mosaic virus (CaMV)
- NOS terminator (TNOS) from Agrobacterium tumefaciens
- 34S promoter (P34S) from figwort mosaic virus (FMV): Monsanto has developed a variety of GM crops with glyphosate herbicide tolerance that utilize the 34S promoter, including MON89788 soy, H7-1 sugar beet and GT73 rapeseed (canola).
To quantitate the GMO level in a particular sample, a combination of broad-spectrum and event-specific qPCR assays is often the most efficient approach (3) .
The Maxwell® RSC PureFood GMO and Authentication Kit used with the Maxwell® RSC Instrument is designed to provide an easy and automated method for efficient purification of DNA used in PCR-based testing for Genetically Modified Organism (GMO) DNA sequences and PCR-based food and ingredient authentication.
The Maxwell® RSC Instrument is supplied with preprogrammed purification methods and is designed for use with predispensed reagent cartridges, maximizing simplicity and convenience. The instrument can purify DNA in approximately 40 minutes from 1 to 16 raw and processed food samples including: corn, soybeans, canola, ground pork, ground beef, pork gelatin, breaded fish, tortillas, corn chips and rice cakes.
In this article, we extracted DNA from a variety of food samples using the Maxwell® PureFood GMO and Authentication Kit and the Maxwell® RSC instrument. The extracted DNA was evaluated for the presence of GM sequences using three qPCR assays:
Amplification Primers (IDT)
|ORFIII (CaMV) (4)
- Forward primer
- Reverse primer
- Probe (FAM-IB FQ/ZEN)
- Forward primer
- Reverse primer
- Probe (HEX-IB FQ/ZEN)
- Universal forward primer
- Universal reverse primer
Maxwell® RSC Protocol
The Maxwell® RSC PureFood GMO and Authentication Kit Technical Manual #TM473 and the Maxwell® RSC Methods Installation Technical Manual #TM435 are available at www.promega.com/protocols/
or by contacting Technical Services at firstname.lastname@example.org.