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Appl Environ Microbiol. 1980 March; 39(3): 642-649

Biology of Azospirillum-Sugarcane Association: Enhancement of Nitrogenase Activity

¹ Department of Botany, University of Florida, Gainesville, Florida 32611
² Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611

ABSTRACT

Azospirillum brasilense was reisolated from associations with callus tissue cultures of sugarcane and compared with stock cultures of the inoculated bacterium and related strains. Although the reisolate had a growth rate similar to stock cultures, it exhibited a severalfold increase in maximum specific activity of nitrogenase. The reisolate and the parent culture had similar ultrastructure. The general ultrastructure of Azospirillum is described. The bacterium was capsulated when grown on nitrogen-free nutrient agar plates and on callus, but was not capsulated when growing in a subsurface zone in N-free semisolid nutrient agar, except rarely in aging cultures. Capsulation may be a protective mechanism against unfavorable pO₂ under dinitrogen-fixing conditions. Pleomorphism occurred in capsulated forms, and the ultrastructure of these forms is described.

Journal series no. 1888, Florida Agricultural Experiment Station, Gainesville, FL 32611.

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