Enhanced yields of iron-oxidizing bacteria by in situ electrochemical reduction of soluble iron in the growth medium.

An electrochemical apparatus for culturing chemolithotrophic bacteria that respire aerobically on ferrous ions is described. Enhanced yields of the bacteria were achieved by the in situ electrochemical reduction of soluble iron in the growth medium. When subjected to a direct current of 30 A for 60 days, a 45-liter culture of Thiobacillus ferrooxidans grew from 6 x 10 to 9.5 x 10 cells per ml. Growth of the bacterium within the electrolytic bioreactor was linear with time. A final cell density corresponding to 4.7 g of wet cell paste per liter was achieved, and a total of 320 g of wet cell paste was harvested from one culture. The apparatus was designed to deliver protons concomitantly with electrons; therefore, the pH of the culture remained stable at 1.6 +/- 0.1 for the duration of growth. This laboratory-scale apparatus may be readily adapted to pilot or production scale. It is thus anticipated that abundant numbers of iron-oxidizing bacteria may be obtained for both fundamental and applied studies.