Temperature sensitive nitrogen fixation mutants of Azotobacter vinelandii.

Abstract

Temperature-sensitive nitrogen fixation mutants of Azotobacter vinelandii were obtained by nitrosoguanidine mutagenesis and penicillin selection. The mutants were unable to grow on N2 at 39° but grew normally at 30° on N2 and at both temperatures in the presence of metabolizable nitrogen compounds. Growth experiments and assays of whole cells for nitrogenase activity separated the mutants into two classes: 1. mutants in which the nitrogenase activity present in cells grown at 30° was unaffected by a shift to 39°, and 2. mutants which lost their nitrogen fixation activity after such a temperature shift. Assays of cell-free extracts of the second class of mutants showed that in all cases tested the enzymatic activity of the nitrogenase complex itself was not affected by the mutation. These mutants might therefore contain some other temperature-sensitive proteins specifically involved in nitrogen fixation.