厌氧氨氧化菌群体感应系统研究

厌氧氨氧化(Anammox)是以铵为电子供体将亚硝酸盐转化为氮气的生物过程。厌氧氨氧化菌(AAOB)生理代谢和细胞结构均十分特殊,且在氮素循环中起着十分重要的作用。厌氧氨氧化已成为环境学、微生物学、海洋学等领域的研究热点。但是,至今人们未能对厌氧氨氧化菌进行纯培养,这严重限制了对厌氧氨氧化菌的深入研究。群体感应是一种普遍存在于微生物细胞之间的通讯机制,它具有根据菌群密度和周围环境变化调节基因表达,以控制细菌群体行为的功能。厌氧氨氧化菌活性的细胞密度效应和生物团聚行为与细菌中普遍存在的群体感应现象相符。探讨了厌氧氨氧化菌群体感应系统存在的可能性、工作机制及其生态学意义,以期为厌氧氨氧化菌的分离培养、团聚体培育等提供理论指导。

Quorum sensing in anaerobic ammonium oxidation bacteria

Anaerobic ammonium oxidation (Anammox)is a unique anaerobic biological reaction which converts ammonium and nitrite into nitrogen gas and plays an important role in the nitrogen biogeochemical cycle. It is now estimated that Anammox might contribute more than 50% to global present day nitrogen losses from the ocean. Anaerobic ammonium-oxidizing bacteria (AAOB) as the responsible chemolithoautotrophic bacteria are grouped into the phylum Planctomycetes. Now a family of Anammoxaceae including five genera, ten species of AAOB are established. AAOB have some distinct characters in the physiology, metabolism and cell structure. AAOB are chemoautotrophic bacteria which use carbon dioxide or bicarbonate as the main carbon source and ammonium or nitrite as the energy source. AAOB produce hydrazine or hydroxylamine as the very unusual intermediates. AAOB have a particular cell wall structure, cell membrane component and inner cell structure. Currently Anammox are one of hot-spots in the fields of environmental science, microbiology and marine science. So far, however, AAOB have not been isolated and cultivated in pure culture, which has become a great obstacle in the related studies. Besides, applications of Anammox process are also limited without making AAOB's characters clear. Quorum sensing may provide us another perspective to understand AAOB. Quorum-sensing is a common signal sensing mechanism by which bacteria monitor their population density.Quorum sensing system allows bacteria to regulate their gene expression according to the population density and the environmental condition so as to alter their behavior on a population scale. The ability of rapidly altering gene expression and consequently behavior in response to a dynamic environment give bacteria the plasticity to survive in rich, neutural and hostile condition. Bacteria communicate with one another using chemical signal molecules termed autoinducers. In quorum-sensing bacteria, chemical communication involves producing, releasing, detecting, and responding to small hormone-like moleculed autoinducers. Bacteria use autoinducers to communicate both within and between species. Both species-specific and specific-nonspecific autoinducers exist. Now there are about four types of autoinducers including acylated homoserine lactone (AHL), oligopeptides, furanosyl borate dister(FBD) and some homologues like epinephrine or norepincphrine in quorum sensing system. Differernt bacteria have differernt quorum sensing network architectures. They include parallel quorum-sensing circuits, sequenced quorum-sensing circuits, competitive quorum-sensing circuits, on-off switches quorum-sensing circuits and so on. As to AAOB, they have shown some quorum sensing characteristics. AAOB take on Anammox activity only when the cell concentration is higher than 10¹⁰-10¹¹ cells/mL. The formation and hydrolysis of extracellular polymeric substances (EPS) have some to do with the population density. Based on the current studies, we firstly analyze the possibility whether AAOB hold a quorum sensing system. Then we discuss the working mechanism of quorum sensing system in AAOB analog to that of Vibrio fischeri and Pseudomonas aeruginosa which are two model microorganisms for quorum sensing study. Finally we explain the ecological significance of quorum sensing to AAOB's survival. All the disscussions aim to give some enlightenment for learning the specific charcaters of AAOB which may be helpful for pure culturing and making better use of Anammox process.