厌氧氨氧化菌细胞的超微结构及功能

Ultrastructure and function of anaerobic ammonium oxidation bacteria cells

厌氧氨氧化菌是浮霉状菌属(Planctomyces)的化能自养型细菌,其在缺氧条件下以亚硝酸盐(NO2-)作为电子受体将氨(NH4+)转化为氮气(N2).该过程具有高效低耗的优点,因而厌氧氨氧化工艺成为目前最具应用前景的污水脱氮工艺,为了更好地将厌氧氨氧化工艺应用到实际规模中,对厌氧氨氧化菌的生物学研究非常必要.近年来,电镜技术的快速发展使得厌氧氨氧化菌超微结构的研究成为可能.厌氧氨氧化菌结构独特,被厌氧氨氧化体膜、胞浆内膜、细胞质膜分隔成厌氧氨氧化体、核糖细胞质及外室细胞质3个部分.本文由内至外地总结和描述了厌氧氨氧化菌的细胞器、膜结构、储存颗粒以及细胞附属物的形态特征,并对他们的功能进行了合理的解释和推测,得出以下结论:1)厌氧氨氧化体占据细胞体积的50%左右,是厌氧氨氧化菌最重要的细胞器,为厌氧氨氧化菌的代谢提供了场所;2)厌氧氨氧化体膜具有致密的阶梯烷膜脂结构,可抵抗有毒中间产物扩散从而保护细胞;3)厌氧氨氧化体内的铁储存颗粒可为血红素提供铁元素从而加快细胞的新陈代谢,而核糖细胞质中的糖原物质与储存颗粒可能分别与生物膜的形成及能量储存有关;4)厌氧氨氧化菌的菌毛可能与细胞黏着或胞间通讯相关,而S-layer对细胞的完整性及细胞形状的维持起着至关重要的作用.目前对厌氧氨氧化菌超微结构的研究还仅局限于生物学方面,建议今后以不同水质及操作条件下厌氧氨氧化细胞超微结构的改变为研究重点.

Anaerobic ammonium oxidation bacteria are chemolitho-autotrophs belonging to a clade of deeply branching Planctomycetes. The anammox bacteria use ammonium as an electron donor for nitrite reduction to dinitrogen gas under anoxic conditions. The anammox process is an attractive treatment option for removing nitrogen from wastewater with high efficiency and low consumption. In order to fully apply this process, it is necessary to study the cell biology of anammox bacteria, which is made possible by the fast development of electron-microscopy technology. The structure of anaerobic ammonium oxidation bacteria cells is special, with three separate compartments of cytoplasm bounded by individual bilayer membranes, namely the anammoxosome membrane, intracytoplasmic membrane, and cytoplasmic membrane, respectively. This study selected the anammox bacteria cells as the research object to investigate and describe the morphological specificity of organelle, membrane structure, storage particles and cell appendages from inside to outside, and make a further explanation and assumption of their functions. We found that 1） the anammoxosome occupies about fifty percent cell volume, with the intracytoplasmic compartment the very important place for anammox catabolism. 2） The ladderane lipids occur in the membrane of the anammoxosome and it can protect the cell from the toxic anammox intermediates. 3） Iron particles in anammoxosome can provide heme with iron to expedite the cell metabolism; the function of glycogen and the riboplasmic particles in riboplasm could be that anammox bacteria store glycogen and riboplasmic particles for biofilm formation and energy storage, respectively. 4） The function of the pilus-like appendages is for adherence to the environment or in cell-to-cell communication, and S-layerof Anammox bacteria plays a key role in maintaining cell shape and integrity. Further researches are suggested to focus on ultrastructure changes in the anammox treatment of different wastewater and operating conditions.