[Effect of lyophilization on the nitrogenase activity of Azotobacter vinelandii]

The activity of nitrogenase in the cells of Azobacter vinelandii grown from lyophilized and non-lyophilized cultures depends on the donor of hydrogen and the concentration of oxygen in the gaseous phase. The lyophilized cells are more sensitive to oxygen (O2 optimum for nitrogen fixation is ca. 1 percent) than the non-lyophilized cells (ca. 5 percent). The determination of acetylene reduction in the course of the culture growth has shown that nitrogen fixation in the lyophilized cells takes place after a lag-period (about six hours) at a rate lower than that of the non-lyophilized cells. The results obtained suggest that lyophilization increases the sensitivity of the cells to oxygen and decreases their nitrogenase activity which is however restored after a while.