Effects Of Transgenic Cotton With Bt And Bt Plus CpTI Gene On Soil Microbial Community Structure

By the methods of plate culture counting, Biolog, PCR-DGGE and PLFA, a comparativestudy was conducted to assess the effects of (long-term) cultivation of transgenic insect-resistentcotton on soil microbial communities, which play an important role in the decomposition oforganic matter and hence are largely exposed to GM plant residues. The experiments carried out inthree different types of cotton-growing areas(Jiangsu, Hubei, Henan province), two pairs oftransgenic insect-resistent cotton (Zhongmian41,GK-12) and their parental conventional cotton(Zhongmian23,Simian3) were used, rhizosphere soil samples (0-20cm) were collected atseeding, budding, boll forming, boll opening and aging stage during the year2010and2011,according to the different growth stages of cottons, we studied the population of culturablemicroorganisms (bacterial, fungal, actinomycetes, denitrobacteria, azotobacter and nitrosobacteria),the functional diversity of microbial metabolism, the diversity of bacterial community, fungicommunity and microbial community structure. The results show that:1. There are obvious influence on the number of culturable microorganisms between two pairsof transgenic insect-resistent cotton and their parental cotton, respectively. Throughout the growingperiod of cotton, comparing to their corresponding line, the number of culturable microorganismsslightly lower in the soil of transgenic Bt cotton, especially the number of bacterial is significantlylower than that of parental line at boll opening stage. However, the number of culturablemicroorganisms slightly higher in the soil of transgenic Bt+CpTI cotton, fungal is significantlyaffect at seeding, boll-forming and boll-opening stages, actinomycetes is significantly influenced atseeding stage. While the number of azotobacter, denitrobacteria and nitrosobacteria is notsignificantly different.2. There are also a certain influence on the carbon source metabolic activity of soilmicrobial,transgenic cotton varieties and cotton growing areas were related. Throughout thegrowing period of cotton, comparing to their corresponding isolines non-transgenic cotton,carbon source metabolic activity of soil microbial slightly lower in the soil of transgenic Bt cotton,which is significantly different at boll-opening stage. However, carbon source metabolic activityof soil microbial slightly higher in the soil of transgenic Bt+CpTI cotton, but only showedsignificantly different at budding stage in Yancheng site.3. PCR-DGGE results suggest that it has a high similarity in bacterial community diversityand fungal community diversity between gene modified cotton and non-GM isoline cotton at samegrowth stage.4. PFLA analysis was accepted as indicator for risk evaluation of transgenic insect-resistentcotton on soil microbial community, in our study, the results showed that there was no significant effect on the type and content of PLFA of soil microbial,which suggest microbial biomass andcommunity structure were stable even at the situation of planting transgenic cotton.5. Sampling date and location were found to greatly influence soil microbial communitystructure. Different sampling time has significant effects on the composition and diversity of soilmicrobial.