Hydrophilic property of Ferroplasma acidiphilum strain was investigated through direct contact angle measurements, interaction with hydrocarbons and with the determination of its surface energy components. The contact angles of three different liquids drops (water, chloroform, and 1-bromonaphthalene) positioned on the bacterial lawn were measured. Hamaker constant, electron donor and electron acceptor parameters were calculated. The results of contact angles and those of the interaction with organic solvents showed that the microbe has hydrophilic property. The value of interaction energy, Delta G(bwb), between two microbial cells (b) immersed in water (w) was found to be +29.53 mJ/m(2) confirming the hydrophilic nature of the microbial cells. The floatability of pyrite under xanthate conditions with and without the microbial cells was examined. The results showed that, when the mineral sample was treated with the microbial cells, the cells rendered their own hydrophilic nature to the mineral surface and the floatability of the mineral decreased dramatically over all pH regions. (C) 2012 Elsevier Ltd. All rights reserved.