Molecular diversity of cytochrome oxidase among Acidithiobacillus ferrooxidans strains resistant to molybdenum, mercury, sulfite and 2,4-dinitrophenol

Five physiologically different strains of Acidithiobacillus ferrooxidans were isolated. Strains Funis 2-1, SUG 2-2, OK1-50 and NASF-1, respectively, are resistant to molybdenum, mercury, sulfite and 2,4-dinitrophenol (2,4-DNP). In contrast, strain AP19-3 is sensitive to all these toxic compounds. Cytochrome oxidase is one of the most important enzymes in the iron oxidation system of A. ferrooxidans. Cytochrome oxidase was purified from the five strains to an electrophoretically homogenous state to clarify the relationship between resistance and molecular structure of the enzyme. The apparent molecular weights of cytochrome oxidase β- and γ-subunits from Funis 2-1, SUG 2-2, OK1-50 and AP19-3 were 24 and 19 kDa, and those of NASF-1, 22.5 and 20 kDa, respectively. The apparent molecular weights of cytochrome oxidases α-subunits of the five strains ranged from 53 to 56 kDa. The N-terminal amino acid sequences of cytochrome oxidase β- and γ-subunits were nearly the same among the five strains except for the γ-subunits of AP19-3. The sequences of α-subunit from AP19-3, OK1-50 and Funis 2-1 differed markedly from each other. The N-terminal amino acid of SUG 2-2 α-subunit was blocked. These results indicate that A. ferrooxidans strains resistant to Mo⁵⁺, Hg²⁺, sulfite and 2,4-DNP have a cytochrome oxidase different from that of the sensitive strain AP19-3 with respect to apparent molecular size as well as N-terminal amino acid sequence.