Journal of Methods Microbiological Journal of Microbiological Methods 36 (1999) 11–19 Fractal analysis to discriminate between biotic and abiotic attacks on chalcopyrite and pyrolusite a a b a, * P. Cardone , C. Ercole , S. Breccia , A. Lepidi a Department of Basic and Applied Biology, University of L’ Aquila, Via Vetoio, Coppito, 67010 L’ Aquila, Italy b Scuola Superiore G. Reiss Romoli, via Giovanni Falcone 25, Coppito, 67010 L’ Aquila, Italy Abstract In the present paper, a model describing release and mobility of copper and manganese in chalcopyrite and pyrolusite powders due to bacterial bioleaching, i.e. Thiobacillus ferrooxidans and Arthrobacter sp., is proposed. Sites where copper and manganese were released were examined by scanning electron microscopy (SEM). The resulting micrographs were scanned and submitted to a point by point fractal analysis to verify if a discrimination between biological and chemical attack could be established on the basis of the distribution of the fractional part of the fractal dimension over the whole surface. We demonstrate that such a method is able to discriminate among the different attacks.  1999 Elsevier Science B.V. All rights reserved. Keywords: Biodeterioration; Bioleaching; Chalcopyrite; Fractal analysis; Pyrolusite 1. Introduction these metals play a mayor role in controlling both the redox balance and the carbon cycling via oxidation Manganese and iron are abundant transition metals in the environments in which they are present with alternating redox states that easily transform abundant (Bromfield and David, 1976). under conditions commonly encountered in nature. Microorganisms are able to promote biochemical Changes in the redox states of both metals are often transformations of iron, copper, manganese and observed at pH boundaries in natural systems, in- mineral sulphides compounds (Lizama and Suzuki, dicating that they are participating in environmental- 1988; Konishi et al., 1992; Bhavaraju et al., 1993; exchange reactions (Nealson, 1994) and greatly Nemati and Webb, 1997). These transformations, influence the biogeochemical cycles of carbon and prevalently of an oxido-reductive kind, modify the others metals (Lovley, 1991; Myers and Nealson, solubility of metals and its distribution in the en- 1992; Lovley and Phillips, 1994). vironment (i.e. soil and water). For many years, geochemists and chemists have Environmental factors and microbial actions are noted a relationship between organic carbon degra- responsible for the formation of manganiferous and dation (oxidation) and the concomitant reduction of chalcopyrite deposits (Nealson, 1983). Oxidative or oxidised manganese and iron and postulated that reductive capabilities are prevailing in microbes isolated respectively from the upper or deeper soil profile sites. Bacteria able to oxidize chalcopyrite *Corresponding author. Tel.: 139-862-433-282; fax: 139-862- and to reduce manganese dioxide are isolated from 433-273. E-mail address: lepidia@aquila.infn.it (A. Lepidi) soil (Le Roux and Wakerley, 1988; Myers and 0167-7012 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0167-7012(99)00006-8