Pseudomonas aeruginosa PAO1 expresses two chemically distinct forms of lipopolysaccharide (LPS) termed A-band and B-band LPS. Strain PAO1 (A\sp+B\sp+) and isogenic LPS mutants (A\sp+B\sp−; A\sp−B\sp+, A\sp−B\sp−) were studied to determine how differences in LPS (surface) chemistry might affect binding of soluble metal cations (Au, Cu, Fe and La). Atomic absorption spectrophotometry, transmission electron microscopy (with energy dispersive X-ray spectroscopy) and selected area electron diffraction revealed that all strains (grown planktonically) bound equal amounts of Cu. Iron precipitated as amorphous hydroxides preferentially on the surfaces of the A\sp−B\sp+ strain. Lanthanum precipitated as apiculate crystals preferentially on the surfaces of the A\sp+B\sp− strain. Gold precipitated intracellularly in all strains as elemental crystals. Biofilms of PAO1 (A\sp+B\sp+) showed a significant increase (relative to planktonic cells) in metal binding for all metals except Cu. The results indicate that metal binding is greatly affected by both the surface chemistry and mode of growth of the cells.