Detection systems for GMO crops

Kimball Nill reports on interference by soil-borne bacteria and micro-organisms when using PCR-based detection methods.

The European Union's proposed mandatory atraceability' law would be impossible to implement in the real world of international commerce. That is because it would force so-called aGMO testing' of imported agricultural commodities (eg, maize, soybeans, canola, etc) to be done at an earlier step in the multi-step pathway between farms and the shelves of European food retailers. In those earlier steps, the aforeign material' (FM) within the raw commodity has not yet been screened-out, since the FM-cleaning step occurs just prior to processing of the commodity to become food or animal feed. FM is all matter, including soybeans and pieces of soybeans, that will pass readily through an 1/8-in sieve, and all matter other than soybeans remaining on the sieve after sieving (eg, small amounts of hulls, straw, and other crop plant materials such as weeds).

A cubic centimetre of typical topsoil contains hundreds of thousands of harmless soil-dwelling bacteria. Just like humans or animals, bacteria must be able to amanufacture' certain critical amino acids (eg, glutamine) in order to grow. Different species of bacteria, plants, and animals utilise somewhat different enzymes to amanufacture' their needed amino acids (ie, from the amolecular building blocks' they each derive via photosynthesis or by consuming food).

The soil bacterium Streptomyces hygroscopicus has a gene (the BAR gene) that causes production of the enzyme called phosphinothricin acetyl transferase (PAT). The soil bacterium Streptomyces viridochromogenes has a gene (known as the PAT gene) that causes production of the same enzyme (ie, PAT). When the BAR or PAT genes from these soil bacteria are inserted via biotechnology methods into crop plants, those (bioengineered) crop plants are essentially immune to herbicides containing glufosinate-ammonium (eg, in herbicide tolerant Liberty Link canola grown in Canada). Other plants (weeds) are killed because glufosinate-ammonium inhibits the amanufacture' of the critical amino acid glutamine in (non-engineered) weed plants.

Similarly, a strain known as CP4 of the soil bacterium Agrobacterium tumefaciens had its gene for the enzyme EPSPS (enolpyruvyl-shikimate phosphate synthase) inserted via biotechnology into certain crop plants to render those crop plants essentially immune to herbicides containing the active ingredient known as glyphosate (eg, in herbicide tolerant Roundup Ready soybeans). Although those crop plants already had a gene for the EPSPS enzyme, that particular plant EPSPS enzyme had not been resistant to glyphosate.

According to Dr Barbara Van Til, the specialist in charge of GMO test technology of GIPSA at the US Department of Agriculture, the primary PCR-based GMO tests used in Europe can be misled by the presence of common bacteria in soil in the FM resulting in incorrectly indicating the supposed presence of a GMO in a shipment of agricultural commodity. p

Enquiry No 42

Kimball Nill is Biotechnology and Technical Issues Director, American Soybean Association, St. Louis, MO, USA. www,ussoymeal.org or www.asa-europe.org

Recent Issues