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Humic Acid Reduction by Propionibacterium freudenreichii and Other Fermenting Bacteria

机译：弗氏丙酸杆菌和其他发酵菌减少腐殖酸

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Iron-reducing bacteria have been reported to reduce humic acids and low-molecular-weight quinones with electrons from acetate or hydrogen oxidation. Due to the rapid chemical reaction of amorphous ferric iron with the reduced reaction products, humic acids and low-molecular-weight redox mediators may play an important role in biological iron reduction. Since many anaerobic bacteria that are not able to reduce amorphous ferric iron directly are known to transfer electrons to other external acceptors, such as ferricyanide, 2,6-anthraquinone disulfonate (AQDS), or molecular oxygen, we tested several physiologically different species of fermenting bacteria to determine their abilities to reduce humic acids.Propionibacterium freudenreichii, Lactococcus lactis, and Enterococcus cecorum all shifted their fermentation patterns towards more oxidized products when humic acids were present; P. freudenreichii even oxidized propionate to acetate under these conditions. When amorphous ferric iron was added to reoxidize the electron acceptor, humic acids were found to be equally effective when they were added in substoichiometric amounts. These findings indicate that in addition to iron-reducing bacteria, fermenting bacteria are also capable of channeling electrons from anaerobic oxidations via humic acids towards iron reduction. This information needs to be considered in future studies of electron flow in soils and sediments.
机译：据报道，还原铁细菌会利用乙酸盐或氢氧化产生的电子来还原腐殖酸和低分子量醌。由于非晶态三价铁与还原的反应产物快速化学反应，腐殖酸和低分子量氧化还原介体可能在生物铁还原中起重要作用。由于已知许多无法直接还原无定形三价铁的厌氧细菌会将电子转移至其他外部受体，例如铁氰化物，2,6-蒽醌二磺酸盐（AQDS）或分子氧，因此我们测试了几种生理上不同的发酵物种当存在腐殖酸时，弗氏丙酸杆菌，乳酸乳球菌和cecorum肠球菌都将其发酵模式转向了更多的氧化产物。在这些条件下，弗氏疟原虫甚至将丙酸酯氧化成乙酸酯。当加入无定形三价铁使电子受体再氧化时，发现腐殖酸以亚化学计量加入时同样有效。这些发现表明，除还原铁细菌外，发酵细菌还能够通过腐殖酸将来自厌氧氧化的电子引导到还原铁。在未来对土壤和沉积物中电子流的研究中需要考虑这些信息。

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