Nitrogenase activity and inactivation in isolated bacteroids from the legume siratro and the non-legume Parasponia rigida

Abstract

We demonstrate continued nitrogenase activity in isolated bacteroids of Rhizobium strain ANU289 from nodules of siratro ( Macroptilium atropurpureum) and the non-legume Parasponia rigida for periods up to 240 min with maximum activities maintained at 52 nmol ethylene produced h −1 mg −1 protein. Both legume and non-legume bacteroids showed a broader oxygen tolerance in the presence of the nodule supernatant. Isolated Parasponia-derived bacteroids exhibited an optimum nitrogenase activity at about 0.1% O 2 in the gas phase, while siratro bacteroids had a slightly higher O 2 optimum. These findings illustrate that (i) Rhizobium bacteroids isolated from a non-legume host are highly oxygen-sensitive for their nitrogenase activity, (ii) the Parasponia nodule supernatant increases the oxygen tolerance of the bacteroids.