Dinitrogen-fixing bacteria: computer-assisted identification of soil isolates

Dinitrogen-fixing (acetylene-reducing) bacteria may be readily isolated from soils but extensive biochemical or immunobiological testing, or both, are required to identify them absolutely. A computer-assisted scheme for identification of nine genera of dinitrogen-fixing bacteria was developed and tested. The computer program is based on interpretation of the 70 biochemical tests of the API 20E and 50E, supplemented with tests for acetylene reduction, nitrate and nitrite reduction, catalase, oxidase, motility, and growth on MacConkey's bile salt medium. Dinitrogen-fixing Enterobacteriaceae (Klebsiella pneumoniae, Enterobacter cloacae, and Erwinia herbicola) were accurately identified using the data base in the API analytical profile index. Nonenteric dinitrogen-fixing bacteria (Azotobacter spp., Azospirillum spp., Derxia sp., Rhodospirillum sp., Clostridium sp., and Bacillus spp.) were subjected to these tests to form a new data base for these bacteria. The API tests agreed with standard biochemical tests commonly used to identify these bacteria, were reproducible with time, and were sufficiently unique to permit accurate identification of each species. The use of the API 20E and 50E tests plus the additional seven tests with these known data bases permitted rapid and precise identification of acetylene reducing bacteria from various agricultural ecosystems.