Impact of Field-Grown Genetically Modified Maize on Native Rhizobacteria

Abstract

Plant-root interaction occurs in the rhizosphere, a region referred to as a biologically active zone of soil where microorganisms and plant roots interact. This study examined the impact of genetically modified (GM) maize (Bt) on functional community of rhizobacteria. Soil samples of field grown GM and non-GM maize were collected from an experimental field in Delmas, South Africa, at 30 days after sowing (DAS) and I day after harvest (DAH). Chemical analyses of soil properties in GM and Non-GM soil samples were performed. Quantitative analysis was achieved through soil dilution and plate count (colony forming units) using selective and non-selective media (tryptic soy agar, nutrient agar, Luria Bertani agar and Pseudomonas selective agar). Qualitative analysis was achieved using analytical profile index identification systems and sequence data of rhizobacterial isolates. Biolog GN2 microplate was used to compare community catabolic profile of rhizobacteria in GM and non-GM soils and denaturing gradient gel electrophoresis technique (DGGE) was used in comparing rhizobacterial community profiles in GM and non-GM soil samples. Chemical analyses of GM and non-GM soil samples collected 30 DAS and 1 DAH indicated the same elements with similar percentages. The pH of GM and non-GM soil samples range from 6.12-7.03, indicating slightly acidic to slightly alkaline soil. Total count of rhizobacteria (cfulg) in GM and non-GM maize soil samples collected 30 DAS and 1 DAH was not significantly different in the media. Similar rhizobacterial species from the rhizosphere of both GM and non- GM maize were identified using analytical profile index and sequence data. No significant difference was observed in the community catabolic profile among the rhizobacteria in GM and non-GM soil samples. Cluster analyses of DGGE bands indicated that band patterns of GM and non-GM samples 30 DAS and 1 DAH were similar to each other. These findings suggest that the GM maize was not able to alter microbial community and activity and are significant to the investigation of the impact of GM maize on rhizobacteria.