Nitrogen-fixing Growth in Continuous Culture of a Strain of Rhizobium sp. Isolated from Stem Nodules on Sesbania rostrata

Abstract

A strain of Rhizobium sp. (ORS571), isolated from stem nodules on Sesbania rostrata, was grown as a N2-fixing continuous culture for up to five weeks (> 80 culture replacements). Under optimum conditions of O2 supply [< 9 m dissolved O2, 100160 nmol O2 (mg dry wt)−1 min−1], N2 fixation rates were 300400 nmol N2 (mg dry wt)−1 h−1 and nitrogenase activity in culture samples reached 2000 nmol C2H4 (mg dry wt)−1 h−1, the highest values yet recorded for any Rhizobium species. Other properties of the continuous cultures are described and a comparison is made with previous reports of N2 fixation by cultures of Rhizobium spp. Significant features were the greater tolerance to O2 of ORS571 and the retention of fixed N in the cells of this strain.