ADAPTATION OF AZOTOBACTER CELLS TO TRICARBOXYLIC ACID SUBSTRATES

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Abstract
Cells of Azotobacter vinelandii. strain Original, grown on sucrose require a lag period before they achieve max. rate of oxidation on citric acid cycle substrates. Previous studies on the characteristics of this "adaptation" are open to question as the reported rates are only 1/3 to 1/2 those that can be obtained with this organism under proper conditions. A re-examination of this physiological characteristic of the azotobacter was undertaken with special emphasis on adaptation to succinate. Adaptation did not occur unless succinate was oxidized; an inhibitor of oxidative assimilation prevented or prolonged adaptation. The following reduced the lag time: Higher temp., simultaneous oxidation of acetate, increased phosphate buffer concn. The azotobacter cells adapted without fixing N. Addition of an external N source raised final activities without affecting rate of adaptation. Mg raised activity during and after the lag period. Lags were lengthened if the initial pH was higher or lower than the opt. of 7, but adaptation occurred from pH 6 to 8. The time of the lag was shorter and activities higher with cells harvested in the stationary phase than with those from the logarithmic phase. Drying the cells eliminated lags on some substrates but not on others. The relation of factors affecting the lag to possible mechanisms involved in the adaptation is briefly discussed.