AUTOTROPHIC AND MIXOTROPHIC GROWTH OF GALLIONELLA-FERRUGINEA

CO2 fixation and uptake of sugars by Gallionella ferruginea were demonstrated by liquid scintillation and microautoradiographic techniques. The theoretical carbon content of a G. ferruginea cell in the exponential and stationary growth phases was calculated from size measurements of images of acridine-orange-stained cells. The carbon content of a cell in the exponential phase was 1.25 x 10(-4) mol and for a cell in the stationary phase it was 5 x 10(-15) mol. G. ferruginea was shown to obtain all of its cell carbon from CO2 fixation when it was cultured under aerobic gradient conditions in a mineral salt solution with iron sulphide. Uptake experiments were performed with 1.6-mu-M-[C-14]glucose, 1.6-mu-M-[C-14]fructose and 1.3-mu-M-[C-14]sucrose. There was significant uptake of all three sugars. Measurements of respired (CO2)-C-14 showed that 48%, 25% and 32% of the total amount of incorporated sugar was respired for glucose, fructose and sucrose, respectively. The uptake of glucose increased when the glucose concentration in the growth medium was increased. At a glucose concentration of 10-mu-M or higher, the cell carbon was derived exclusively from glucose, within the errors of estimation. Mixotrophic growth with 20-mu-M-glucose decreased the CO2 fixation to 0.4 x 10(-14) mol carbon per cell, compared to autotrophically grown cells with 1.0 x 10(-14) mol carbon per cell. The addition of 20-mu-M-glucose gave an increase in cell number in the stationary phase from 1 x 10(6) to 5 x 10(6) cells ml-1.