NITROGEN-FIXING BACILLUS SPECIES FROM EGYPTIAN SOILS - ACETYLENE-REDUCTION AND CULTURAL CONDITIONS

Among 390 isolates from Egytiian soils initially grown on Brown's N-free agar, 15 facultative Bacillus isolates were able to reduce acetylene in Stanier's N-poor broth under both aerobic and anaerobic (N2 atmosphere) conditions. Some of these isolates were Gram-positive, with unswollen sporangia and thin-walled endospores. Other strains were with slightly or definitely bulged sporangia. Yeast extract (0.01%) was essential for growth stimulation and N2[C2H2] fixation by these isolates. Replacing yeast extract with 20 μg/ml (NH4)2SO4 or biotin, thiamine and amino acids (singly or in combination) resulted in stimulation of growth and N2[C2H2] fixation, though at lower rates than in yeast extract. One isolate was able to grow and reduce C2H2 in Stanier's N-free liquid medium. Nitrogenase [C2H2] activity of the anaerobically grown and incubated cultures was greater than aerobic cultures. Addition of 0.1% CaCO3 to the culture media significantly increased and O2 partially inhibited, N2[C2H2] fixation by these Bacillus isolates. Studies of the characteristics and N2[C2H2] fixing activities of these isolates indicate that at least some of them are new nitrogen-fixing Bacillus species. © 1979 Martinus Nijhoff.