Differences in the Antigenic Pattern of Azotobacter grown on Different Nitrogen Sources

Abstract

THE presence of hydrogenase in nitrogen-fixing bacteria is ascribed a specific significance, as this enzyme is considered to take part in the fixation of gaseous nitrogen¹. This assumption is based on several observations. First, a significantly higher hydrogenase activity has been demonstrated in Azotobacter cells assimilating molecular nitrogen instead of combined forms of nitrogen, for example, ammonium ions, nitrate or glutamic acid. Secondly, Azotobacter mutants which have lost their capacity for nitrogen fixation also displayed a low hydrogenase activity as compared with the wild type. Thirdly, an extract of Clostridium pasteurianum with a retained capability for nitrogen fixation was also shown to contain hydrogenase activity. A fraction containing the hydrogenase activity which is separated from the extract loses its ability to fix nitrogen. Recombination of the fractions restored the activity¹. The site of the hydrogenase activity in ^Azotobacter has been located to the surface components of the cell^2,3.