On Carbohydrate Consumption by Azotobacter chroococcum

Abstract

In a previous paper (Allen, '19) devoted mainly to the study of the cause of beneficial action resulting from mechanical agitation of Azotobacter solution cultures, the defects of existing experimental methods for the study of the physiology of this organism were pointed out. The present report covers a continuance of these studies aimed at the following improvements: (1) renewal of the energy source in the cultures; (2) simultaneous determinations of nitrogen and of residual carbohydrate at short intervals; and (3) mechanical improvements. The object of the first of these improvements was, of course, to produce heavier growths in the cultures and therefore more marked changes in the amounts of metabolic products, thus increasing the reliability of the measurements of such changes. In view of the theoretical considerations of Duclaux ('98-'00) in regard to the rate of increase in the number of cells, we were justified in expecting a mounting rate of total physiological activity as growth proceeded, until the normal rate of development was checked by the accumulation of unfavorable by-products. The method of renewal of energy-supplying material has been used, for example, with marked success by Bonazzi ('19) in his investigations of the organisms of nitrification. The second improvement was designed to furnish a more complete picture of growth processes of Azotobacter than is obtainable by the determination of one, or even two, metabolic products at the end of an arbitrarily chosen incubation period. Unfortunately, the micro determination of carbohydrate and nitrogen on the same sample proved moredifficult than was expected, and had to be postponed for the time being. The present work, therefore, lacks this improvement over that reported previously. The third improvement was to facilitate experimental manipulation and possibly obtain even better results from mechanical agitation. The type of agitation decided upon was a slow