肺炎克氏杆菌nifA基因在巴西固氮螺菌固氮基因表达的铵调节中的作用

Effect of Klebsiella pneumoniae nif A on the Regulation of nif Gene Expression by Ammonia in Azospirillum brasilense

固氮螺菌(Azospirillum)是一类仅在限铵和微好氧条件下固氮的微生物,它可与许多禾本科作物联合共生,具有较大的应用潜力。铵作为固氮作用的调节信号,在固氮螺菌的实际应用中是首要的限制因素。在固氮螺菌中,铵不但具有与肺炎克氏杆菌(Klebsiella pneumoniae)相似的阻遏固氮酶合成的作用,而且还对已合成的固氮酶进行活性调节。

Plasmid pCK3, which carried a constitutive nifA gene of Klebsiella pneumoni-ae, was transferred into a dra T- mutant strain of Azospirillum brasilense. It was found that pCK3 could not derepress nif gene expression of A. brasilense under high concentration of ammonia. Combined with the result of the phenotypes of the kanamysin resistant gene from pCK3 in A. brasilense under different incubated conditions, it demonstrated that NifA activity was inhibited by ammonia. We suppose that there is a negative regulator in A. brasilense, although not existing in K. pneumoniae, wihich has effect on NifA activity by ammonia.