Surface chemical characterisation of Paenibacillus polymyxa before and after adaptation to sulfide minerals

A heterotroph Paenibacillus polymyxa bacteria is adapted to pyrite, chalcop yrite, galena and sphalerite minerals by repeated subculturing the bacteria in the presence of the mineral until their growth characteristics became s imilar to the growth in the absence of mineral. The unadapted and adapted b acterial surface have been chemically characterised by zeta-potential, cont act angle, adherence to hydrocarbons and FT-IR spectroscopic studies. The s urface free energies of bacteria have been calculated by following the equa tion of state and surface tension component approaches. The aim of the pres ent paper is to understand the changes in surface chemical properties of ba cteria during adaptation to sulfide minerals and the projected consequences in bioflotation and bioflocculation processes. The mineral-adapted cells became more hydrophilic as compared to unadapted cells. There are no significant changes in the surface charge of bacteria b efore and after adaptation, and all the bacteria exhibit an iso-electric po int below pH 2.5. The contact angles are observed to be mon reliable for hy drophobicity assessment than the adherence to hydrocarbons. The Lifschitz-v an der Waals/acid-base approach to calculate surface free energy is found t o be relevant for mineral-bacteria interactions. The diffuse reflectance FT -IR absorbance bands for all the bacteria are the same illustrating similar surface chemical composition. However, the intensity of the bands for unad apted and adapted cells is significantly varied and this is due to differen t amounts of bacterial secretions underlying different growth conditions. ( C) 2001 Elsevier Science B.V. All rights reserved.