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

An experimental study of the attachment of a pure strain of Thiobacillus fe rrooxidans (R2) on films of synthetic pyrite was conducted. Pyrite films re presenting a wide range of structural and electronic properties were produc ed by sulfuration of pure iron films at different annealing temperatures, i .e.: 250, 300, 350, 400, 450 and 500 degrees C. Attachment experiments were conducted contacting pyrite with microorganisms in an iron-free basal medi um at pH = 1.6, Results showed that the patterns and degree of attachment o f 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 de grees C), where there is a major presence of amorphous pyrite, attachment r esults in the formation of elongated clusters of densely packed bacteria. I n the high range of sulfuration temperatures (400, 450 degrees C), where fo rmation of highly crystallized pyrite predominates, attached bacteria are m ainly present as isolated bacteria or forming short pearl-string-like chain s. The percentage of pyrite surface coverage by T. ferrooxidans decreases a t high sulfuration temperatures, where pyrite is fully crystallized. The mi croorganisms seem to attach preferentially to the less crystallized or amor phous zones of the pyrite films which provide a better availability of sulf ide ions for bacterial oxidation. (C) 1999 Published by Elsevier Science B. V. All rights reserved.