环境微生物学-郑平-教学课件-9物质循环.pptVIP

* * * * * * * * * * * * * * * Figure: 17-39 Caption: Electron transport and energy conservation in sulfate-reducing bacteria. In addition to external hydrogen H2 originating from the catabolism of organic compounds such as lactate and pyruvate can fuel hydrogenase. The enzymes hydrogenase, cytochrome , and a cytochrome complex (Hmc) are periplasmic proteins. A separate protein functions to shuttle electrons across the cytoplasmic membrane from Hmc to a cytoplasmic iron-sulfur protein that supplies electrons to APS reductase (forming SO32- ) and sulfite reductase (forming H2S). * * * * Figure: 17-27a Caption: Oxidation of reduced sulfur compounds by sulfur chemolithotrophs. (a) Steps in the oxidation of different compounds. The sulfite oxidase pathway accounts for the majority of sulfite oxidized. * * * * * * * Figure: 17-38b Caption: Biochemistry of sulfate reduction. (b) Schemes of assimilative and dissimilative sulfate reduction. * * * * * * * * Figure: 17-70b Caption: Nitrogenase function. (b) Hypothetical steps in N2 reduction showing the H2 evolution step, and a summary of nitrogenase activity. * * * * * Figure: 19-65_4-6 Caption: Steps 4-6 in the formation of a root nodule in a legume infected by Rhizobium. For a photomicrograph of an infection thread, see Figure 19.66a. For photos of root nodules, see Figures 19.62 and 19.64. Formation of the bacteroid state is a prerequisite for nitrogen fixation. * * * * * * * * * * * * * * * * * * * * * * * 微生物溶磷机理： （1）产生有机酸，促进磷酸盐的溶解。某些二羧酸和三羧酸是很强的螯合剂，能够有效降低钙、铁、铝对磷酸盐的结合，使磷酸盐释放出来。 （2）产生无机酸（如硝化作用产生硝酸），促进磷酸盐的溶解。 （3）释放二氧化碳，产生碳酸，促进含磷矿石的风化。在微生物分解有机物质的过程中，可释放大量二氧化碳，在水溶液中转化成H2CO3和HCO3-，促进含磷矿石风化。 （4）在厌氧条件下，一些微生物能使磷酸高铁盐中的Fe3+还原为Fe2+，使之溶解度提高而促进磷酸盐游离。 返回 * * 五、磷酸盐还原 在一般情况下，磷酸盐不能被微生物还原，但当环境中不存在硫酸盐、硝酸盐和氧时，磷酸盐也可能作为电子受体而被还原。 H3PO4 → H3PO3 → H3PO2 → PH3 PH3易挥发，遇氧自燃，产生蓝色火焰。在有机物质被大量降解的坟堆和沼泽附近，有时可见PH3产生。PH3遇氧自燃后，可点燃这些环境中产生的沼气而诱发“鬼火”。 返回 * * Thank you ! 返回 * * * * * * * * *