Trace Metal Requirements of Azotobacter.

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Abstract
Trace metal requirements of Azotobacter vinelandii O were compared when the organism was utilizing ammonia and gaseous N as N sources. Molybdenum and Ca are specifically required for the N fixation pro- cess. The requirement of Fe is spared when ammonia is the N source. Changes in the level of Fe in the medium do not effect the inhibition of N fixation by H, but high levels of Fe markedly stimulate the knallgas reaction of the organism. Molybdenum tested at levels from 0.001 to 1.0 ppm had no effect on the H inhibition or the knallgas reaction. Low levels of Ca cause an increase in the length of lag phase of a culture using gaseous N. Lowering the P concentration in the presence of low levels of Ca results in a further extension of the lag phase. If the Ca level is optimal, P concentration has no effect on the length of lag. Ammonia completely eliminates the effect of Ca and P on the lag phase.

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