(Color online) Classical DLVO predictions of interaction energy between S. oneidensis MR-1 cells and generalized (A) magnetite and (B) hematite surfaces. (C) Approach curves, recorded using atomic force microscopy employing MR-1 cells immobilized on APTES functionalized Si3N4 cantilevers, to magnetite and hematite surfaces. A Hamaker constant of 3.22 × 10-21 Nm was assumed (Ref. 47), ζ potentialCELL was measured at -5.7 mV in 32 mM PIPES buffer (pH 7.2); ζ potentialMINERAL was based upon pHPZC of 6.6 ± 0.4 and 8.3 ± 0.9 for magnetite and hematite, respectively (Ref. 40). DLVO calculations were performed for an ionic strength of 32 mM. Energy-to-force conversions were calculated as described by Cail and Hochella (Ref. 44).