Study On The Distribution, Diversity And Activity Of Anammox Bacteria In The Sediments Of Lake Taihu

The discovery of anaerobic ammonium oxidation(anammox)process has remarkably changed the knowledge of microbial N cycling process in the past twenty years(Jetten et al.2009).Traditionally,the denitrification process was regarded as the sole microbial process to produce dinitrogen gas,while the discovery of the anammox process not only brings the possibility of NH4+ oxidation coupling NO2-reduction to produce dinitrogen gas(Mulder et al.1995),but also has been widely used in N-rich wastewater treatment system(Kartal et al.2010).Recently,anammox bacteria have been found in various natural ecosystems such as marine,terrestrial and freshwater ecosystems(Humbert et al.2010,Hu et al.2011),however,anammox bacterial distribution,community composition,diversity and nitrogen-removal rates in eutrophic sediments are far from complete,and the major environmental factors driving anammox bacteria are still unclear.In this study,the eutrophic lake sediments of the Taihu Lake were selected as samples,and the horizontal and vertical distribution characteristics of anammox bacteria in 0-10 cm sediments were measured and the main environmental driving factors were explored.The microelectrode system was used to determine the physicochemical properties,such as dissolved oxygen(DO)and redox potential(Eh)in the sediments.Quantitative PCR was used to determine the abundance of ammonia-oxidizing microorganisms.Illumina Miseq high-throughput sequencing,denaturing gradient gel electrophoresis(DGGE)and cloning library were used to determine the microbial communities.Besides,the N transformation rates of anammox process and denitrification process in the sediments were measured by 15N isotope technique.We aim to evaluate the molecular ecology and activity characteristics of anammox bacteria in the sediments of Taihu Lake.The main results are as follows:(1)The abundance of ammonia-oxidizing microorganisms in the sediments at Meiliang Bay(ML),Gonghu Bay(GH)and Xukou Bay(XK)in the Taihu Lake showed that the abundance of anammox bacteria and AOB at ML site were significantly higher than those at GH and XK,while the AOA abundance at ML was significantly lower than that at the other two sites.Two-way ANOVA analysis showed the abundance of anammox bacteria,AOA and AOB at 0-5 cm sediments were significantly higher than those at 5-10 cm sediments.The linear regression results showed that the TN,NH4+-N and TOC content were the key environmental factors affecting the anammox bacterial abundance,while the DOC with TOC content and the TN with NO2-N content were the key factors affecting AOA and AOB abundance,respectively.There were significant differences between ML and other two sites in the community composition of anammox bacteria and AOB in Taihu Lake sediments by cluster analysis.The TN,NO2--N,pH,TOC/TN and DOC content were the important factors shaping their communities.In summary,the 0-5cm sediments was the concentrated area of microorganisms conducting aerobic/anaerobic ammonia oxidation function.Compared with the plant type in the lake,the nutrient level might has more intense effects on the distribution and community of anammox bacteria and AOB.(2)The vertical distribution of anammox bacteria in the sediments of Meiliang Bay(HN)and central lake(LN)with different nitrogen levels showed that the relative abundance of anammox bacteria at LN increased at first and then decreased with the increasing depth with a peak at the 2-4 cm.The anammox bacterial relative abundance at HN varied insignificantly with the increasing depth.Considering the quantitative results of anammox bacteria and total bacteria,we conclude that the distribution traits may be related to the competition of anammox bacteria against other bacteria.In addition,the community composition analysis showed that Candidatus Brocadia spp.,accounting for 83.5-100%of the total anammox bacteria,is the most important anammox bacteria at all sediments.Candidatus Kuenenia spp.is detected at each depth at LN,while it is only distributed at 4-5 cm at HN.Regression analysis and RDA analysis indicated that TN and NH4+-N contents were the most important factors affecting the relative abundance and community composition of anammox bacteria.In addition,the diversity index of anammox bacteria has significant differences between sampling sites,and the DOC,TOC,NH4+-N content and pH were main driving factors.Thus,we infer that the nutrient level of the sediments is the main cause to the vertical variation of the molecular ecology traits of anammox bacteria in the Taihu Lake.(3)The anammox rates in the 0-10 cm sediments of Lake Taihu ranged from 4.3�2.9 nmol N2 g-1 h-1 to 30.3�11.5 nmol N2 g-1 h-1,which was significantly higher than the denitrification rates in sediments.Both rates were no significant difference among ML,XK and GH sites.Regression analysis showed that the NH4+-N and TOC/TN in the sediments were the key factors affecting anammox and denitrification rates,respectively.In addition,the carbon source and pH control experiments also showed that acidic conditions and the addition of carbon sources had a significant inhibitory effect on anammox rates,while alkali conditions promoted the anammox rates.Therefore,we inferred that anammox bacteria might play an important role to N remove especially in the lower-carbon algae-type lake sediments in the Taihu Lake.