Plectonema boryanum UTEX 485, a filamentous cyanobacterium, has been reacted with aqueous Au(S2O3)(2)(3-) and AuCl4- solutions (similar to 400-550 mg/L Au) at 25-100 degrees C for up to I month and at 200 degrees C for I day. The interaction of cyanobacteria with aqueous Au(S2O3)(2)(3-) promoted the precipitation of cubic (100) gold nanoparticles (< 10-25 nm) at membrane vesicles and admixed with gold sulfide within cells and encrusted on the cyanobacteria, whereas reaction with AuCl4- resulted in the precipitation of octahedral (111) gold platelets (similar to 1-10 mu m) in solutions and nanoparticles of gold (< 10 nm) within bacterial cells. Functional groups imaged by negative ion TOF-SIMS on (111) faces of the octahedral platelets were predominantly Cl and CN, with smaller amounts of C2H and CNO.