Enumeration of culturable bacteria colonies on nitrogen fixing medium (NFM) and LB medium conducted by this study revealed statistically significant difference among various soil samples collected from both transgenic Bacillus thuringiensis (Bt) rice fields and non-transgenic Bacillus thuringiensis (Bt) rice field.The transgenic Bt rice had generated impact on the quantities of microorganism communities in soil.Similar results were obtained by measuring shoot lengths after seeds germination.This also suggested that the planting of transgenic Bt rice may affect rice cultivation in the same field.However,such inhibitory effect was often transient in duration.Phylogenetic tree of 16S rDNAs showed a great genetic diversity of our isolated nitrogen fixation bacteria strains,and found that the majority of clones were related to two groups:one group belongs to the classes of Actinobacteria and the other group is Proteobacteria including α-Proteobacteri,more than half of nitrogen fixation bacteria (92％) in the rhizosphere belong to Actinobacteria.The sequences of the 16S rDNAs and the Nitrogenase iron protein coding genes (nifH) of eight nitrogen-fixing bacteria isolated from the transgenic Bt rice soil field were also compared.A lack of phylogenetic congruence of the nifH genes and 16S rDNAs might indicate the occurrence of relatively recent in situ horizontal transfer of the nifH gene,possibly as a direct or indirect consequence of transgenic Bt rice.%通过对具有不同种植年限和不同种植强度的转Bt基因水稻与非转Bt基因水稻土壤中的细菌以及固氮细菌群落结构进行研究,发现转Bt水稻的种植可能会影响土壤中微生物群落的多样性,但是这种影响的可能只是暂时的,通过对测量种植水稻的芽长实验也得出相似的结论.另外,根据16S rDNA基因构建的系统发育进化树揭示了本实验分离的固氮细菌的遗传多样性,发现实验土壤中的固氮细菌主要分为放线菌门(Actinobacteria) (92％)和α-变形菌门(α-Proteobacteria)两大类.分离出的8株典型的固氮菌株,其16S rDNA基因和固氮基因nifH的序列两者的分布不一致,nifH的分布更为紧凑,为固氮基因可能发生了原位水平基因转移提供了证据.
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