Autotrophic and mixotrophic growth of Gallionella ferruginea

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Abstract
C02 fixation and uptake of sugars by Gaffioneffa ferrughea 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 mol and for a cell in the stationary phase it was 5 x 10-l5 mol. G. ferruginea was shown to obtain all of its cell carbon from C02 fixation when it was cultured under aerobic gradient conditions in a mineral salt solution with iron sulphide. Uptake experiments were performed with 1.6 pM-( 14C)glucose, 1.6 pM-( 4C)fructose and 1.3 pM-( 14C)sucrose. There was significant uptake of all three sugars. Measurements of respired 14C02 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 p~ or higher, the cell carbon was derived exclusively from glucose, within the errors of estimation. Mixotrophic growth with 20 p~- glucose decreased the COz 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 pM-glucose gave an increase in cell number in the stationary phase from 1 x lo6 to 5 x lo6 cells ml-l.

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