Extension of logarithmic growth of Thiobacillus ferrooxidans by potential controlled electrochemical reduction of Fe(III)

In this study, we demonstrated that the period of logarithmic growth for Th iobacillus ferrooxidans could be extended when optimal conditions for cell growth were maintained using potential controlled electrochemical cultivati on with sufficient aeration. The optimal pH and Fe(ll) concentration for th e electrolytic cultivation were determined to be 2.0 and 150 mM, respective ly. When the potential was set to 0.0V vs Ag/AgCl, the Pt electrode reduced Fe(lll) to Fe(li) with an efficiency of 95%. a porous glass microbubble ge nerator was used to maintain adequate levels of dissolved oxygen, which was the electron acceptor for T. ferrooxidans when the cell density in the med ium was high. Under these conditions, cells at an initial density of 10(7) cells/mL grew logarithmically for 4days until the cell density was 4 x 10(9 ) cells/mL. This corresponded to a period of logarithmic growth that was 3 times longer than was observed in batch cultures without electrolysis. In a ddition, the final cell density reached 10(10) cells/mL after 6 days of ele ctrochemical cultivation, which was a 50-fold increase over conventional ba tch culture. Under conditions of increasing cell density, potentiostatic el ectrolysis made it possible to remove Fe(III), which causes product inhibit ion, at an increasing rate and to correspondingly increase the production r ate of Fe(II), which is the electron donor for T. ferrooxidans. Thus, our c ultivation system provides a sufficient supply of electron donor and accept or for T. ferrooxidans, thereby elongating the period of logarithmic growth and producing very high cell densities. (C) 1999 John Wiley & Sons, inc.