[Cloning sequencing and expression pattern, functional analysis of nifA gene in Azospirillum brasilense Yu62].

The nifA gene of Azospirillum brasilense Yu62 was cloned and sequenced. The expression of nifA gene was investigated in wild type strain Azospirillum brasilense Yu62. The results show that expression of nifA gene is not repressed by ammounium and oxygen completely. But the expression of Yu62 nifA gene is different from that of strain Sp7 nifA gene. Expression of Yu62 nifA seems more sensitive to oxygen than that of Sp7 nifA which shows the highest expression in condition of aerobic, while the Yu62 nifA gene shows the highest expression in the condition of microaerobic. The regulation of NifA protein activity by ammonia and oxygen was investigated. Results showed that the NifA protein is repressed by ammonia, 1 mmol/L NH4Cl can inhibit activity of NifA protein completely. Oxygen concentration affects activity of NifA protein. NifA protein is highly active in 0.4%-0.5% O2.