水稻联合固氮菌质粒的鉴定及固氮(nif)基因定位

应用改进的Casse法提取质粒,鉴定了供试菌株的质粒存在情况:高NH_4~+和N_2培养的Alcaligenes faecalis A_15,Enterobacter cloacae E26,E.cloacaeEnSs和klebsiella planticola DWUL2分别携有1—2个大质粒,分子量在30—200Md之间;K.planficola和Pseudomonas saccharophila含有小质粒;K.oxytocaNG13不携质粒。供试菌株中DNA与nif探针R1 nif DH和Ec nif B-Y均具有同源性。A.faecalis A15,E.cloacae E26和K.oxytoca NG13的nif基因位于染色体上,而E.cloacae EnSs的nif基因则位于一个较大质粒上。

PLASMID VISULIZATION AND NIF GENE LOCATION IN SEVERAL NITROGEN-FIXING BACTERIA ASSOCIATED WITH RICE PLANTS

By using modified Casse method the plasmids from several species ( strains ) of diazotrophs associated with rice plants, namely Alcaligenes fae-calis Al5, Enterobacter cloacae E26, E.cloacae EnSs, Klebsiella planticola DWUL2, K.oxytoca NG13 and Pscudomonas saccharophila,have been isolated and detected. Except K .oxytoca all bacteria described above were found to harbour plasmids. Among them A.faecalis, E .cloacae E26 and EnSs and K.planticola contained one to two large plasmids ranged from 30-200 Md. Using Southern blot and hybridization technique, homologies were observed between restricted DNA from bacteria described previously and Rhizobium leguminosarum nif DH and E .cloacae nif B-Y.Nif gcne clusters were located on the chromosome for A.faecalis, E .cloacae E26 and K .oxytoca,and on the larger plasmid for E .cloacae EnSs. The results also show that the nif DH and nif B-Y genes in the NH4+-grown cells of A.faecalis were the same as in the N2-grown cells despite of the nitrogcnase activity being absent.