Attachment of Thiobacillus ferrooxidans on synthetic pyrite of varying structural and electronic properties

Abstract

An experimental study of the attachment of a pure strain of Thiobacillus ferrooxidans (R2) on films of synthetic pyrite was conducted. Pyrite films representing a wide range of structural and electronic properties were produced by sulfuration of pure iron films at different annealing temperatures, i.e.: 250, 300, 350, 400, 450 and 500°C. Attachment experiments were conducted contacting pyrite with microorganisms in an iron-free basal medium at pH=1.6. Results showed that the patterns and degree of attachment of T. ferrooxidans to synthetic pyrite are strongly dependent on the degree of crystallization of the sulfide films, which varies with the sulfuration temperature. In the low range of sulfuration temperatures (250, 300, 350°C), where there is a major presence of amorphous pyrite, attachment results in the formation of elongated clusters of densely packed bacteria. In the high range of sulfuration temperatures (400, 450°C), where formation of highly crystallized pyrite predominates, attached bacteria are mainly present as isolated bacteria or forming short pearl-string-like chains. The percentage of pyrite surface coverage by T. ferrooxidans decreases at high sulfuration temperatures, where pyrite is fully crystallized. The microorganisms seem to attach preferentially to the less crystallized or amorphous zones of the pyrite films which provide a better availability of sulfide ions for bacterial oxidation.