Distribution And Horizontal Gene Transfer Of Exogenous Recombinant Dna From Transgenic Bt Cotton In Soil Environment

Molecule behavior and distribution of exogenous recombinant DNA from transgenic Bt cotton in soil is an important part of the environmental risk assessment of genetically modified plants. In this study, we studied the dynamics and spatial characteristics of exogenous recombinant DNA from transgenic Bt cotton, horizontal gene transfer of antibiotic resistant gene, the effect on community structure and abundance of Ammonia-oxidizing bacteria(AOB) and Ammonia-oxidizing archaea(AOA) in soil based on field trials by real-time quantitative PCR, terminal restriction fragment length polymorphism, colony PCR and bioinformatics methods. This study can provide theoretical support for comprehensive evaluation of the biosafety of transgenic Bt cotton. The main results were as follows:1. The dynamic changes of copy number of different exogenous recombinant DNA fragments from transgenic Bt cotton were coincident. The copy number of 35S-Cry1 A and 35S-NPTⅡ fragments from transgenic Bt cotton increased firstly and then decreased with the growth periods. The results showed the maximum of copy number appeared in boll-forming stage, except that the maximum of 35S-NPTⅡfragments appeared in budding stage. There was no significant difference of exogenous recombinant DNA fragment between boll-forming stage and budding stage, but significantly before and after sowing(p<0.05).2. Distribution of 35S-Cry1 A and 35S-NPTⅡfragments from transgenic Bt cotton in different size soil aggregates were in accordance. The maximum copy numbers of both the fragments were all in 500μm~2000μm size, which were significantly more than that in other sizes(p<0.05).3. According to Kanamycin-resistant bacterial culture results, Kanamycin-resistant bacteria were found in soil during seedling stage, budding stage, boll-forming stage and boll opening stage of cotton.-Cloning and sequencing NPT II gene, some differences were found between resistant bacteria and transgenic Bt cotton, which meant no exogenous recombinant NPTⅡ gene from transgenic Bt cotton was detected.4. The dominant population of-AOB and AOA –from transgenic Bt cotton soil was same as control with no significant difference during the growth periods, but disparity with cotton varieties. During whole growth periods, there was no significant difference of Shannon index and Evenness index of soil AOB between transgenic Bt cotton and control. Soil AOA of transgenic Bt cotton, whose Shannon index was no significant difference with control, but Evenness index was significantly lower than control at the seedling stage(p<0.05)and no significant difference with control at other stages. In comparatively, the abundance of soil AOB of transgenic Bt cotton was higher than control at the boll-forming stage, but lower than control at other three stages. During all four stages, the abundance of AOA of transgenic Bt cotton was lower than control. Transgenic Bt cotton had no significant impact on the community structure of soil AOB and AOA, but reduced their quantity, suggesting potential impacts of transgenic Bt cotton on soil ammonia-oxidizing microorganisms.