Optimal conditions for growth and magnetosome formation of Acidithiobacillus ferrooxidans

Abstract

Magnetotactic bacteria (MTB), which contain nano-scale membrane bound crystals of magnetic iron minerals, are of great interest in microbiology, biomineralization, advanced magnetic materials and bio-geosciences. However, no application has been exploited on a commercial scale due to the fastidious lifestyle of most cultured MTB. Acidithiobacillus ferrooxidans is a facultatively aerobic bacterium which can synthesize intracellular electron dense magnetite magnetosomes. Although the mass cultivation of A. ferrooxidans was performed facilely, the optimal conditions for cell growth and magnetosome formation remain unknown. In this study, transmission electronmicroscopy (TEM) and inductively coupled plasma atomic emission spectrometer (ICP-AES) were used to observe magnetosomes and measure iron content of A. ferrooxidans, respectively. The effects of ferrous sulfate concentration, ammonium sulfate concentration, oxygen concentration, pH and temperature on the cell growth and magnetosome formation were systematically investigated. Additionally, the orthogonal design of experiments were carried out, and the optimum conditions for cell growth (FeSO4 120 mM, (NH4)2SO4 3.0 g/L, temperature 30°C, initial pH 1.75, and 20% loadings) and magnetosome formation (FeSO4 160 mM, (NH4)2SO4 2.4 g/L, temperature 20°C, initial pH 1.75, and 50% loadings) were not identical. Key words: Magnetotactic bacteria, Acidithiobacillus ferrooxidans, magnetosome formation, orthogonal design, transmission electronmicroscopy, optimization.