Semiaerobic induction of bacteriochlorophyll synthesis in the green bacterium Chloroflexus aurantiacus

Comparison of Chloroflexus aurantiacus J-10-fl cells by freeze-fracture electron microscopy showed that cell shape and dimensions did not depend on oxygen tension or light intensity during growth. The major morphological difference between cells cultured anaerobically in the light and aerobically in the dark was the absence of chlorosomes in aerobically grown cells. C. aurantiacus cells cultured aerobically in the dark began bacteriochlorophyll synthesis immediately when shifted to either phototrophic or semiaerobic conditions. Cells adapting to phototrophic conditions grew to the same density and synthesized as much bacteriochlorophyll as nonadapting phototrophic cultures grown at the same light intensity. Cells adapting to reduced oxygen tension (semiaerobic conditions) in the dark entered an 8- to 12-h growth lag during which the bacteriochlorophyll content increased significantly. Despite variations in the initial bacteriochlorophyll content and in the length of the growth lag, the amounts of bacteriochlorophyll a and c were constant at the end of the semiaerobic growth lag. At later times during adaptation to semiaerobic conditions, after growth resumed, variations in the ratio of bacteriochlorophyll c/bacteriochlorophyll a were observed and suggested independent regulation of the two bacteriochlorophylls.