Effect Of Transgenic Maize On Bacterial Community In Rhizosphere Soil

Genetically Modified(GM)Crops are kinds of genetically engineered crops,which contain integrated artificially isolated or modified exogenous genes in their genomes by genetic engineering technology.The exogenous genes could be stably inherited to the next generation in GM crops.In general,the original traits of GM crops will be replaced by new stable traits,such as herbicide resistance,insect resistance and disease resistance.The safety and stability of soil ecosystem is one of the important conditions to ensure the sustainable and healthy development of agriculture,and soil microorganisms are the key point in the biological structure of soil.The planting of transgenic maize enables Bt protein to enter the soil ecosystem through a variety of ways.With the development of commercialized cultivation of GM crops,people pay more attention to the ecological security risk of GM crops.In this study,we adopted multiple methods,including plate culture,high-throughput sequencing and enzyme-linked immuno sorbent assay(ELISA)to evaluate the potential risk of transgenic maize Shuangkang 12-5 on the rhizosphere soil microorganisms.In addition,we also detected the degradation dynamics of Bt protein content in rhizosphere soil at various developmental period of transgenic maize Shuangkang 12-5,comparing with Xianyu 335.The results provided new information for the environmental safety evaluation of transgentic maize Shuangkang 12-5.The main results of this study are listed as follows:(1)The results of plate culture showed that there was no significant difference in the biomass of fungi and actinomycetes isolated from rhizosphere soil between transgenic maize Shuangkang 12-5 and its parental control at different developmental period.Shuangkang 12-5 showed similar changes of the five functional bacteria to Xianyu 335,the diversity and distribution uniformity of the colony were the most abundant at the tassel stage and the lowest at the jointing stage.But the dominant concentration was the most obvious at the jointing stage.Except the aerobic nitrogen-fixing bacteria at the silking stage and the aerobic fibre-decomposing bacteria in trumpet stage,the bacterial quantity of other rhizosphere soil bacteria of Shuangkang 12-5 and Xianyu 335 showed no significant difference at other developmental period.(2)High-throughput sequencing analysis showed that Shuangkang 12-5 and Xianyu335 had the same dominant microflora.A total of 44 phyla,435 families and 842 genera were obtained.Proteobacteria,Actinobacteria,Acidobacteria and Chloroflexi were the dominant bacteria,accounting for more than 10% of the samples in each growth period.The dominant bacteria had a roughly same trend in the whole growth period of Shuangkang 12-5 and Xianyu 335.It showed significant differences in Gaiellales during the whole growth period.The abundance of this strain in rhizosphere soil of the transgenic corn was higher than the parent controls.There were significant differences between the bacteria in the rhizosphere soil of the two groups of maize in some of the developmental period.For example,there were significant differences in community abundance in seven genera of bacteria between the two kinds of maize in silking stage,milking stage and ripening stage.Samples at the milky stage and ripening stage had the largest number of strains that show significant differences.For example,Gaiella showed significant differences,Gemmatimonadaceae and MSB-1E8 showed extremely significant differences in the two groups of maize at the milky stage.At the ripening stage,srains of Nitrosomonadaceae,MSB-1E8,Gaiella and Anaerolineaceae showed significant differences,while Gaiellales had extremely significant differences between the two groups of samples.The diversity of bacterial community was basically same in the rhizosphere soil of the two groups of maize,and the biggest difference of community diversity was in the ripening stage.(3)ELISA analyses revealed that the content of Bt toxin protein in rhizosphere soil of transgenic corn Shuangkang 12-5 changed dynamically with the development of maize growth.It reached the maximum at tassel stage and the minimum at bell-bottom stage.After straw returning to the field,Bt toxin protein was degraded rapidly at the early stage,slowed down at the middle stage and micro-degraded at the later stage.When the straw was returned to the field for 170 days,the content of Bt toxin protein in the sample was less than 0.2ng/g.The Bt toxin protein will not accumulate in soil ecosystem for a long time.