Effect of Bt-transgenic cotton pot cultivation on rhizosphere and non-rhizosphere bacterial community

In this study, effects of T2 Bacillus thuringiensis (Bt) transgenic cotton (line 61) and its non-transgenic line on bacterial dynamics were investigated during the cotton development stages (seedling, squaring, flowering and boll formation) using culturable (viable plate count) and unculturabale (polymerase chain reaction-denaturing gradient gel electrophoresis, PCR-DGGE) assays. The number nitrogen-fixing bacteria, organic and inorganic phosphate-dissolving bacteria in the rhizosphere soil were also determined by cultivation on specific growth media. Viable plate count analysis showed an increase in the number of total bacteria in rhizosphere soils of both transgenic and non-transgenic cultivars as compared to the bulk soil. PCR-DGGE confirmed the results of viable plate count assays. No significant differences in number of functional bacteria were observed between rhizosphere soil of Bt transgenic and non-transgenic cotton at one particular stage. However, significant differences in bacterial population size in rhizosphere soil observed during the cotton development stages in both transgenic and non-transgenic plants, but not for bulk soil. The results indicated that Bt transgenic cotton (line 61) might have no adverse effects on community structures and total number of culturable bacteria in the rhizosphere.