The electrochemical measurement and surface analysis methods were carried out to investigate the corrosion behavior of steel A3 in Thiobacillus ferrooxidans, streptomyces and T. f-streptomyces mixed colony systems. Results showed that asymmetric biofilms adhered on the surface of steel A3 after 7 days of exposure in different corrosive systems; pitting corrosion occurred on the surface of steel A3 after 7 days of exposure in T. f and streptomyce solutions, but an even corrosion appeared in T. f-streptomyces mixed colony solution; weight loss in the mixed colony system was between those caused by each individual microorganisms; the electrochemical impedance spectroscopy results indicated that the impedance value of steel A3 in the mixed colony system was the medium of those in T. f and streptomyces system. Above results revealed that the most serious corrosion occurred in the streptomyces system, secondly for the T. f-streptomyces mixed colony solution, and corrosiveness of the T. f solution was the lightest to steel A3.

Key words: Thiobacillus ferrooxidans, streptomyces, mixed colonies, corrosion, electrochemical impedance spectroscopy