Protection of nitrogenase levels in dark-incubated cultures of Anabaena sp. strain CA by various carbon sources, and restoration of nitrogenase activity by oxygen

Abstract

Photoautotrophically grown, nitrogen-fixing cultures of Anabaena sp. strain CA lost nitrogenase activity completely after 4 h of incubation in the dark. The original level of nitrogenase activity was restored within 3 h of re-illumination and was apparently dependent on de novo protein synthesis. Several organic carbon sources protected nitrogenase activity. The heterocysts isolated from photoautotrophically grown cultures incubated in the dark (35 min) showed negligible nitrogenase activity. When these heterocysts were exposed to oxygen, glucose or fructose during isolation, normal activity was observed only with O₂. Oxygen also enhanced the rate of initial H₂ evolution from isolated heterocysts.