Accumulation of Fe, Cr and Ni Metals inside Cells of Acidophilic Bacterium Acidiphilium rubrum that Produces Zn-Containing Bacteriochlorophyll a

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The accumulations of metals were studied in cells of aerobic acidophilic proteobacterium Acidiphilium rubrum; this spices uses Zn, instead of Mg as the central atom of bacteriochlorophyll in its photosynthetic apparatus. Energy dispersive X-ray analysis (EDX) of the cell surfaces gave peaks of P, S, Si and Mg.Transmission electron micrograph images showed a high density globule of 0.11 μm in diameter in each 1.1 × 0.3 μm cell. An EDX analysis of the black precipitate that was collected after the contrifugation of disrupted cells showed high amounts of the heavy metals Fe, Cr, Ni and traces of K, Ca, P, Si and Al in the order of atomic content. An X-ray powder diffraction analysis indicated that Fe, Cr and Ni exist as alloys. The metal accumulations interpret the high tolerance of this bacterium to the toxic heavy metals abundant in acidic growth medium. Zn seems to specifically exist as Zn-bacteriochlorophyll a in this organism, because no significant accumulation of Zn was detected on the cell surface, black precipitate, or cytoplasmic membranes.