An inducible hydrogenase in cyanobacteria enhances N 2 fixation

Nz-Fixing cyanobacteria (blue-green algae) Nostoc muscorum and dnabaena cylindrica have been reported to contain hydrogenase activity [ 1,2] . In a recent study from this laboratory it was found that e this activity is present both in heterocysts and vegetative cells of aerobically-grown cultures of both species [3,4]. However, it is not known whether the hydrogenase activity in these organisms is inducible. In the earlier studies of Fujita et al. [2] activity was obtained only after activation, similar to activation of hydrogenase activity that has been reported in green algae (cf. Kessler [S]) which occurs after incubation for several hours under Hz gas. Induction of Hz-uptake activity has also been reported in chemolitotrophic bacteria by Canevascini and Eberhardt [6]. Various Na-fixing bacteria also possess Hz-uptake activity [7,8] and a link between hydrogenase and nitrogenase activity was suggested by Dixon [8] which has received further emphasis in a recent analysis of Hz production in various Ns-fixing organisms by Schubert and Evans [9]. Furthermore, Smith et al. [lo] and Bothe et al. [l I] have reported that hydrogenase can recycle Hz gas lost by nitrogenase . In the present investigation two questions have been examined: first, whether hydrogenase in N. muscorum and A. cylindrica is an inducible enzyme and, secondly, whether there is a cooperativity between the uptake of Hz catalyzed by hydrogenase and the rate and efficiency of N*-uptake catalyzed by nitrogenase in aerobically and Hz-grown cultures of these microorganisms.