Changes in Respiratory Activity during Encystment of Azotobacter vinelandii

Vegetative cells of Azotobacter vinelandii were induced to encyst in the presence of β-hydroxybutyrate. Although modal cell volume fluctuated (2.7 to 4 μ;m3) markedly during exponential growth, the final modal volume attained by mature cysts (1.13 to 1.3 μ;m3) was relatively constant. Respiratory activity of encysting cultures fell rapidly 3 h after initiation of encystment. This was accompanied by decreased inhibition of respiration by KCN. NADH oxidase activity of membrane preparations fell from approximately 450 to 50 nmol O2 consumed min-1 (mg protein)-1 during differentiation and was also less sensitive to KCN. Difference spectra of cytochromes in membrane preparations revealed a number of changes. Amounts of cytochromes b, c and a 1 all fell during encystment; cytochrome o levels increased whilst cytochrome oxidase d was gradually lost from the membrane during the first 22 h of morphogenesis.