The affinity of Rhodococcus opacus cells for calcite and magnesite surfaces has been studied in order to evaluate its application as a flotation collector. The surface properties of minerals and R. opacus were characterized using infrared techniques. The mineral spectrums, before and after the bacterial interaction, indicated a mineral surface interaction with thee R. opacus cell wall. The results were compared with the zeta potential curves as a function of the pH. The cell wall composition of R. opacus was characterized and the R. opacus hydrophobicity was either evaluated with contact angle measurements. The interfacial tension components were calculated based on the van Oss and Fowkes equations. The obtained results were supported by DLVO and X-DLVO theories for selected pH values. The results show the paramount innovation that R. opacus presents as a biocollector and its possible application in the mineral flotation industry. (c) 2007 Elsevier Ltd. All rights reserved.