ENHANCED YIELDS OF IRON-OXIDIZING BACTERIA BY IN-SITU ELECTROCHEMICALREDUCTION 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 reductio n of soluble iron in the growth medium. When subjected to a direct cur rent of 30 A for 60 days, a 45-liter culture of Thiobacillus ferrooxid ans grew from 6 x 10(7) to 9.5 x 10(9) cells per mi. Growth of the bac terium within the electrolytic bioreactor was linear with time. A fina l 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 on e 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 antic ipated that abundant numbers of iron-oxidizing bacteria may be obtaine d for both fundamental and applied studies.