Ultrastructure And Iron Regulation Mechanism Of Anammox Bacteria

Anaerobic ammonia-oxidizing(Anammox)bacteria widely exist in natural ecosystems and are a kind of important chemoautotrophic microorganisms.It obtains energy from the oxidation of ammonium with nitrite to nitrogen gas,and the nitrogen gas produced by anammox bacteria are estimated to account for up to 50%of the nitrogen cycle.Anammox process has been successfully applied to biological denitrification of wastewater and presents good nitrogen removal performance.The total nitrogen removal rate is up to 9.5 kg M^-3 d^-1.It has the advantages of being environmentally friendly and cost-effective.Suspended anammox bacteria have a high loss in practical engineering applications.Anammox granules have high sludge retention and strong impact resistance.Anammox granules combine the advantages of granular sludge and anammox bacteria.Anammox granules are dark red and rich in iron.Mature anammox bacteria are also dark red due to the abundant iron element and cytochrome,and called as"red bacteria".However,the mass transfer process of iron from anammox granules to single bacteria was still unknown,and the regulation mechanism of the abundant iron in anammox bacteria was still vacant.The structure and function of anammox granules and single anammox bacteria were studied,and the regulation mechanism of iron in anammox bacteria was explored in this study.This provided a new understanding of the regulation of iron in the anammox process.The main contents and results of this study are as follows:In order to study the internal microstructure of the anammox granules,the three-dimensional nondestructive structure of anammox granules was imaged and analyzed by X-ray tomography and Feldkamp reconstruction algorithm.The three-dimensional structure and internal pore structure of anammox granules were obtained,and the three-dimensional structure of anammox granules at different growth period was analyzed.The structural characteristics and community structure of anammox granules at different growth stages were obtained.The in situ nondestructive ultrastructure of intact anammox bacteria was imaged by coupled synchrotron soft X-ray imaging technology and simultaneous algebraic reconstruction technique with the total variation algorithm(SART-TV).The anammoxosome and nanoparticles with high X-ray absorption were detected,and the average linear absorption coefficients(LAC)of anammoxosome and nanoparticles were0.389±0.001?m^-1 and 0.460±0.001?m^-1,respectively.The chemical composition and structure of the high soft X-ray absorption composition were determined.Dual-energy imaging was used to study the distribution of highly absorbed nanoparticles.It was found that the nanoparticles with high soft X-ray absorption were iron-rich nanoparticles.The bacterioferritin Q1Q315(kuste3640)and Q1Q5F8(kuste4480),which could store large amounts of iron atoms,were detected by proteomics.The biological significance of iron-rich nanoparticles was clarified.The local atomic structure of iron-rich nanoparticles was analyzed by X-ray fine spectroscopy,and the local atomic structure model of iron-rich nanoparticles was obtained.It was found that the local atomic structure of iron-rich nanoparticles was similar to that of iron oxide.The regulation mechanism of iron nanoparticles and iron elements in anammox bacteria was studied.Iron plays an important role in the anammox process.Under the condition of iron deficiency,the growth and nitrogen removal performance of anammox bacteria were significantly inhibited,and the expression of major enzymes involved in the anammox process decreased.After exposure to Fe NPs,the porosity and matrix diffusion coefficient of anammox granules were increased,thus resulting in more nutrients diffusing into anammox granules,and more iron-containing protein synthesis in anammoxosome.Furthermore,the key enzymes involved in the anammox process are up-regulated and enhanced the anammox process.In addition,the expression of bacterioferritin was up-regulated,and more available iron elements are stored in bacterioferritin and further dynamically regulate the anammox process.Based on the proteomic analysis structure,the regulatory mechanism of iron in anammox bacteria was obtained.