GM microbes invade North America.

• Author: Cummins, Joe
• Position: Thinking Ecologically

A number of GM microbes are being widely deployed since their first release six years ago. Sinorhizobium meliloti is a bacterium added to soil or inoculated into seeds to enhance nodule formation and nitrogen fixation in the roots of legumes, released in 1997.

The other commercial GM microbes are designated as biopesticides. These include GM Agrobacterium radiobacter k1026, used to prevent crown gall disease in fruit and vegetables, and Pseudomonas fluorescens modified from Bacillus thuringiensis (Bt). The modified cultures are killed by heat and provide a persistent biopesticide that degrades much more slowly in sunlight than Bt.

Neither the people selling nor those using these preparations are necessarily aware that the microbes are genetically modified. Even organic farmers may be using them inadvertently.

The legume symbiont, Sinorhizobium meliloti, is tremendously important for fixing nitrogen from the air into plant roots and the soil. The genetically modified commercial strain (RMBPC-2) has genes added that regulate nitrogenase enzyme (for nitrogen fixation) along with genes that increase the organic acid delivered from the plant to the nodule bacterium. It also has the antibiotic resistance marker genes for streptomycin and spectinomycin. The commercial release was permitted in spite of concerns about the impact on the environment.

Evidence supporting the initial concerns has accumulated but not dampened the use of the GM microbe. For example, a recent review reports that GM S. meliloti strains persisted in the soil for six years, even in the absence of the hosts. Horizontal gene transfer to other soil bacteria and microevolution of plasmids was observed. Other studies showed that a soil microarthropod ingested GM S. meliloti, and then a GM E. coli in the gut facilitated gene transfer to a range of bacteria.

There is little doubt that the antibiotic resistance markers for streptomycin and spectinomycin will be transferred to soil bacteria and to a range of animal pathogens. The resistance genes for streptomycin could be observed to transfer to infecting bacterium when homologous gene sequences were present.

The antibiotics spectinomycin and streptomycin are used extensively in human and animal medicine. Spectinomycin treats human gonorrhea and bovine pneumonia. Streptomycin treats human tuberculosis and Meniere's disease and is used as a pesticide on fruits and vegetables.

The commercial release of GM Sinorhizobium meliloti has...