In vitro expression of nitrogenase activity in Parasponia-Rhizobium strain ANU 289

Rhizobium strain ANU 289 derepressed nitrogenase activity under defined in vitro conditions. Acetylene reduction was detected both in agar and liquid stationary culture. The strain is capable of nitrogen-fixing nodulation of legumes [such as siratro (Macroptilium atropurpureum Urb] as well as the non-legumes Parasponia andersonii and P. rugosa. Nitrogenase activity as high as 40-70 nmol C2H4 per mg protein after 7 days of incubation was detected. Strain ANU 289 was similar to Rhizobium strains 32 H1 and CB 756 with regard to oxygen requirement in the gas phase for development of nitrogenase activity between 0 and 10% O2, but showed increased sensitivity to oxygen repression at 20% O2. Strain ANU 289 also showed pronounced sensitivity to exogenous glutamine compared to strains 32 H1 and CB 756.