Nitrogen Fixation and Nitrate Respiration by A zospirillum brasilense

Abstract

The O2- sensitivitiy of N2-fixation by the carotenoid forming strain Azospirillum brasilense Cd and the colourless strain Sp 7 is compared in the present communication. As no difference in the reaction is observed with both strains, it is concluded that carotenoids do not protect nitrogenase from damage by O2. Azospirillum spp. have also been shown to perform NO3-- dependent N2-fixation. The physiological properties of this reaction are described in more detail in the present communication. Evidence is presented that NO3-- dependent N2-fixation is a transitory reaction, proceeding only as long as the enzymes of assimilatory nitrate reduction are synthesized by the cells.

Effect of Carotenoid Overproduction on Oxygen Tolerance of Nitrogen Fixation in Azospirillum brasilense Sp7

“…Carotenoid pigments were extracted from the cells with acetone/ methanol (7 : 2, v/v) according to Nur et al (1981). Carotenoid concentrations were calculated from the absorbance at 500 nm of the acetone/methanol extract, using an absorption coefficient of 2500 for a 1 % (w/v) solution (Britton & Goodwin, 1971). To determine individual pigments, the extracts were evaporated, redissolved in a small volume of chloroform, and chromatographed on silica gel thin-layer plates with methanol/chloroform (7 : 93, v/v) as solvent.…”