EFFECT OF DISSOLVED OXYGEN ON ELECTRON TRANSPORT SYSTEM OF AZOTOBACTER VINELANDII IN GLUCOSE-LIMITED AND OXYGEN-LIMITED CHEMOSTAT CULTURES

[摘要] A glucose-limited and an oxygen-limited chemostat cultivations of Azotobacter vinelandii were carried out to secure the cells, different in the spectrum of the electron transport system relevant to respiration.Cellular contents of cytochromes c (c4+c5) and b1 decreased monotonously with the increase in dissolved oxygen concentration to an extent of 40× 10-6M in the chemostat cultures and then, leveled off. The maximum values of the content which appeared in a specific run of the oxygen- limited chemostat were two to three times those observed in the leveled-off region. Other cellular contents of cytochrome a2 and flavoprotein, however, were insensitive to the whole range of dissolved oxygen concentration (= 2.2 to 180×10-6M) in both types of the chemostat culture.Respiration rate of the bacterial cells thus harvested was measured by the exhaustion method; Km values in the Michaelis-Menten equation were not definite; the value of Km (=17×10-6M) with respect to the cells sampled from a specific chemostat with an extremely low level of dissolved oxygen (=2.2×10-6M) became larger with release from the stringent oxygen-limited condition in the chemostat cultures and approached infinite when the limiting factor of oxygen was replaced completely by glucose, i.e., dissolved oxygen became sufficient, in the original cultures.An intracellular spectrum of electron carrier, high energy metabolite, and dissolved oxygen, all participating in the enzymic reaction of cytochrome oxidase, were incorporated into the reaction model to elaborate on the respiration rate which was highly affected by the culture "career" of the bacterial cells.

[学科分类] 微生物学和免疫学