Kashefi K, Lovley D R
Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Appl Environ Microbiol. 2000 Mar;66(3):1050-6. doi: 10.1128/AEM.66.3.1050-1056.2000.
It has recently been noted that a diversity of hyperthermophilic microorganisms have the ability to reduce Fe(III) with hydrogen as the electron donor, but the reduction of Fe(III) or other metals by these organisms has not been previously examined in detail. When Pyrobaculum islandicum was grown at 100 degrees C in a medium with hydrogen as the electron donor and Fe(III)-citrate as the electron acceptor, the increase in cell numbers of P. islandicum per mole of Fe(III) reduced was found to be ca. 10-fold higher than previously reported. Poorly crystalline Fe(III) oxide could also serve as the electron acceptor for growth on hydrogen. The stoichiometry of hydrogen uptake and Fe(III) oxide reduction was consistent with the oxidation of 1 mol of hydrogen resulting in the reduction of 2 mol of Fe(III). The poorly crystalline Fe(III) oxide was reduced to extracellular magnetite. P. islandicum could not effectively reduce the crystalline Fe(III) oxide minerals goethite and hematite. In addition to using hydrogen as an electron donor for Fe(III) reduction, P. islandicum grew via Fe(III) reduction in media in which peptone and yeast extract served as potential electron donors. The closely related species P. aerophilum grew via Fe(III) reduction in a similar complex medium. Cell suspensions of P. islandicum reduced the following metals with hydrogen as the electron donor: U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV). The reduction of these metals was dependent upon the presence of cells and hydrogen. The metalloids arsenate and selenate were not reduced. U(VI) was reduced to the insoluble U(IV) mineral uraninite, which was extracellular. Tc(VII) was reduced to insoluble Tc(IV) or Tc(V). Cr(VI) was reduced to the less toxic, less soluble Cr(III). Co(III) was reduced to Co(II). Mn(IV) was reduced to Mn(II) with the formation of manganese carbonate. These results demonstrate that biological reduction may contribute to the speciation of metals in hydrothermal environments and could account for such phenomena as magnetite accumulation and the formation of uranium deposits at ca. 100 degrees C. Reduction of toxic metals with hyperthermophilic microorganisms or their enzymes might be applied to the remediation of metal-contaminated waters or waste streams.
最近人们注意到，多种嗜热微生物能够以氢气作为电子供体来还原Fe(III)，但此前尚未对这些生物对Fe(III)或其他金属的还原作用进行详细研究。当嗜热栖热菌（Pyrobaculum islandicum）在100摄氏度下，以氢气作为电子供体、柠檬酸铁(III)作为电子受体的培养基中生长时，发现每还原1摩尔Fe(III)，嗜热栖热菌的细胞数量增加量约比之前报道的高10倍。结晶度差的Fe(III)氧化物也可作为利用氢气生长时的电子受体。氢气摄取与Fe(III)氧化物还原的化学计量关系与1摩尔氢气氧化导致2摩尔Fe(III)还原一致。结晶度差的Fe(III)氧化物被还原为细胞外的磁铁矿。嗜热栖热菌无法有效还原结晶态的Fe(III)氧化物矿物针铁矿和赤铁矿。除了利用氢气作为还原Fe(III)的电子供体外，嗜热栖热菌还能在蛋白胨和酵母提取物作为潜在电子供体的培养基中通过还原Fe(III)生长。亲缘关系相近的嗜热栖气菌（P. aerophilum）能在类似的复合培养基中通过还原Fe(III)生长。嗜热栖热菌的细胞悬液以氢气作为电子供体还原了以下金属：U(VI)、Tc(VII)、Cr(VI)、Co(III)和Mn(IV)。这些金属的还原依赖于细胞和氢气的存在。类金属砷酸盐和硒酸盐未被还原。U(VI)被还原为不溶性的U(IV)矿物晶质铀矿，其位于细胞外。Tc(VII)被还原为不溶性的Tc(IV)或Tc(V)。Cr(VI)被还原为毒性较小、溶解性较差的Cr(III)。Co(III)被还原为Co(II)。Mn(IV)被还原为Mn(II)并形成碳酸锰。这些结果表明，生物还原可能有助于热液环境中金属的形态转化，并可解释磁铁矿积累以及约100摄氏度下铀矿床形成等现象。利用嗜热微生物或其酶还原有毒金属可能应用于金属污染水体或废水流的修复。
