Investigation on gene transfer from genetically modified corn (Zea mays L.) plants to soil bacteria

Abstract

Knowledge about the prevalence and diversity of antibiotic resistance genes in soil bacteria communities is required to evaluate the possibility and ecological consequences of the transfer of these genes carried by genetically modified (GM) plants to soil bacteria. The neomycin phosphotransferase gene (nptII) conferring resistance to kanamycin and neomycin is one of the antibiotic resistance genes commonly present in GM plants. In this study, we investigated kanamycin-resistant (Km^R) and neomycin-resistant (Nm^R) soil bacterial populations in a 3-year field trial using a commercial GM corn (Zea mays L.) carrying the nptII gene and its near isogenic line. The results showed that a portion (2.3 – 15.6 %) of cultivable soil bacteria was naturally resistant to kanamycin or neomycin. However, no significant difference in the population level of Km^R or Nm^R soil bacteria was observed between the GM and non-GM corn fields. The nptII gene was not detected in any of the total 3000 Km^R or Nm^R isolates screened by PCR. Further, total soil bacterial cells were collected through Nycodenz gradient centrifugation and bacterial community DNA was subjected to PCR. Detection limit was about 500 cells per gram of fresh soil. Our study suggests that the nptII gene was relatively rare in the soil bacterial populations and there was no evidence of gene transfer from a GM corn plant to soil bacteria based on the data from total soil bacterial communities.

Keywords:

• Soil microbial ecology; genetically modified (GM) corn; soil bacteria; antibiotic resistance; kanamycin; neomycin; real-time PCR.

Acknowledgments

This work was a joint cooperative research between Environment Canada and Agriculture and Agri-Food Canada, and was financially supported in part by the Canadian Environmental Protection Act (CEPA) and the Strategic Applications of Genomics in Environmental Research (STAGE) grants. We are indebted to Dr. Yiu-Kwok Chan for proofreading of the manuscript. AAFC-ECORC contribution No.: 11-148.

This article is dedicated to Dr. Bin Zhu, a Research Scientist from Environment Canada, who passed away in May 2010.