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

Abstract

In this study, we demonstrated that the period of logarithmic growth for Thiobacillus ferrooxidans could be extended when optimal conditions for cell growth were maintained using potential controlled electrochemical cultivation with sufficient aeration. The optimal pH and Fe(II) concentration for the electrolytic cultivation were determined to be 2.0 and 150 mM, respectively. When the potential was set to 0.0V vs Ag/AgCl, the Pt electrode reduced Fe(III) to Fe(II) with an efficiency of 95%. A porous glass microbubble generator was used to maintain adequate levels of dissolved oxygen, which was the electron acceptor for T. ferrooxidans when the cell density in the medium 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 addition, the final cell density reached 10(10) cells/mL after 6 days of electrochemical cultivation, which was a 50-fold increase over conventional batch culture. Under conditions of increasing cell density, potentiostatic electrolysis made it possible to remove Fe(III), which causes product inhibition, at an increasing rate and to correspondingly increase the production rate of Fe(II), which is the electron donor for T. ferrooxidans. Thus, our cultivation system provides a sufficient supply of electron donor and acceptor for T. ferrooxidans, thereby elongating the period of logarithmic growth and producing very high cell densities.

Growth of non-phototrophic microorganisms using solar energy through mineral photocatalysis

“…The chemical reductant ascorbic acid (12.5 g l − 1 ) in electrolyte KCl (2.5 g l − 1 ) served as the scavenger of positively charged holes in the P-chamber. Unless specially stated, the C-chamber contained various mixtures including: Fe 3 + and/or Fe 2 + solutions in the m9K medium 45 (see below for its specific composition); a Fe 3 + /Fe 2 + solution containing A. ferrooxidans in the m9K medium; Luria-Bertani medium containing A. faecalis; and a red soil slurry in sterile soil extract as an electrolyte. One modification was made to the m9K medium for the sphalerite/goethite experiments.…”

“…The reference electrode was a saturated calomel electrode (SCE, 0.242 V corrected to a normal hydrogen electrode (NHE)), which was placed close to the working electrode. 45 was used for isolation of A. ferrooxidans (see Supplementary Methods for the isolation procedure). This isolate was identified as A. ferrooxidans (100% similarity) by sequencing the nearly full length of the 16S rRNA gene (GenBank accession number HQ603786).…”

<i>Acidithiobacillus ferrooxidans</i> as a Bioelectrocatalyst for Conversion of Atmospheric CO₂ into Extracellular Pyruvic Acid

“…Recently, electrochemical cultivation has been proposed as an effective method for yielding high densities of A. ferrooxidans cells. 6 For example, Matsumoto et al 7,8 reported that the potential-controlled cultivation of A. ferrooxidans using electrodes with large surface areas effectively generated Fe 2+ and extended the logarithmic growth period, with cell density reaching concentrations comparable to that for heterotrophic bacteria (10 10 cells mL ¹1 ). However, the chemical composition of the organic compounds synthesized by A. ferrooxidans in batch cultures and the fraction of the secreted compounds in total fixed carbon during electrochemical cultivation have remained largely uncharacterized.…”

Electrochemical Regeneration of Fe(III) To Support Growth on Anaerobic Iron Respiration

“…In this system, the electrode provided electrons to the aerobic respiratory chain of the bacterium via iron (3,5,12,13). However, as a practical matter, this electrochemical help is available to only a few iron oxidizers that derive energy for growth from aerobic iron respiration.…”

“…Each medium contained (per liter of distilled water) 133 mg of (NH 4 4 . An Ag-AgCl reference electrode situated in the anolyte bath between the anode and the cation-exchange membrane was used to control the anodic potential (12). The entire apparatus was placed in an airtight box (width, 30 cm; depth, 30 cm; height, 25 cm) and incubated at 30°C with an atmosphere containing 80% H 2 and 20% CO 2 at a pressure of 250 kPa.…”