The respiratory system and diazotrophic activity of Acetobacter diazotrophicus PAL5

The characteristics of the respiratory system of Acetobacter diazotrophicus PALS were investigated. Increasing aeration (from 0.5 to 4.0 liters of air min(-1) liter of medium(-1)) had a strong positive effect on growth and on the diazotrophic activity of cultures, Cells obtained from well-aerated an d diazotrophically active cultures possessed a highly active, membrane-boun d electron transport system with dehydrogenases for NADH, glucose, and acet aldehyde as the main electron donors. Ethanol, succinate, and gluconate wer e also oxidized but to only a minor extent. Terminal cytochrome c oxidase-t ype activity was poor as measured by reduced N,N,N,N'-tetramethyl-p-phenyle nediamine, but quinol oxidase-type activity, as measured by 2,3,5,6 tetrach loro-1,4-benzenediol, was high. Spectral and high-pressure liquid chromatog raphy analysis of membranes revealed the presence of cytochrome ba as a put ative oxidase in cells obtained from diazotrophically active cultures. Cell s were also rich in c-type cytochromes; four bands of high molecular mass ( i.e,, 67, 56, 52, and 45 kDa) were revealed by a peroxidase activity stain in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. KCN inhibitio n curves of respiratory oxidase activities were biphasic, with a highly res istant component, Treatment of membranes with 0.2% Triton X-100 solubilized c-type cytochromes and resulted in a preparation that was significantly mo re sensitive to cyanide, Repression of diazotrophic activity in well-aerate d cultures by 40 mM (NH4)(2) SO4 caused a significant decrease of the respi ratory activities. It is noteworthy that the levels of glucose dehydrogenas e and putative oxidase ba decreased 6.8- and 10-fold, respectively. In thes e cells, a bd-type cytochrome seems to be the major terminal oxidase, Thus, it would seem that glucose dehydrogenase and cytochrome ba are key compone nts of the respiratory system of A. diazotrophicus during aerobic diazotrop hy.