Effect Of Bt Transgenic Rice (KMD) On Soil Bacterial Community And Rhizosphere AM Fungi

There have been few investigations of the possible effects ofgenetically engineered plants on the microbiota in flooded soil. Westudied the influence of the transgenic rice Kemindao (KMD) straw onthe culturable anaerobic bacteria and bacterial community composition ina flooded paddy soil under laboratory conditions. KMD contained asynthetic crylAb gene from Bacillus thuringiensis under the control of amaize ubiquitin promoter and linked in tandem with the gusA and hptgenes. The experiments were conducted in plastic pots each containing1500g air-dried fluvio marine yellow loamy soil amended either with 3%(w/w) Bt-transgenic rice straw, 3% (w/w) parental rice straw or no straw.Nine hundred mL sterile distilled water was added to submerge the soil.The flooded soils were then incubated in the dark at 28±1℃. Soilsamples were taken from each pot at defined intervals over the incubationto assay for anaerobic bacteria and bacterial community composition.Results showed that there were only some occasional significantdifferences (P<0.05) in the number of anaerobic fermentative bacteria,denitrifying bacteria, hydrogen-producing acetogenic bacteria, andmethanogenic bacteria between the paddy soils amended withBt-transgenic rice straw and with non-Bt parental rice straw during theearly stage of incubation. Bacterial community composition wasdescribed by denaturing gradient gel electrophoresis (DGGE) DNAfingerprints of amplified soil bacterial 16S rRNA genes. The DGGEfingerprints showed that there were apparent differences in thecomposition of the bacterial community between soil amended with Bt-transgenic rice straw and non-Bt parental rice straw from three weeks to five weeks of incubation, but there were few differences in bacterial community composition between two soils after eleven weeks of incubation. However, both soils to which rice straws were added demonstrated significant differences in the number of anaerobic microorganisms and bacterial community composition with respect to the control soil over the entire incubation. The above results indicated that, under the laboratory conditions, the Bt-straw from KMD has no long-term negative effects on a variety of culturable anaerobic bacteria and bacterial community composition in the studied flooded paddy soil.Field studies were performed to investigate the effects of Bt crylAb gene transfer into the rice genome on the number of rhizosohere AM fungi and rice residue decomposition. Results showed that there were no significant differences in number of rhizosohere AM fungi between Bt transgenic rice and non-Bt parental rice. In addition, no significant differences in the decomposition rate between rice residues due to the transfer of Bt crylAb gene into rice genome.