Nitrogen And Carbon Removal Metabolic Mechanism Of Typical Aerobic Denitrifying Bacteria

Nitrogen is the essential element in the cycle of nutrients and biogeochemistry.With the development of global modernization and urbanization,the impact of human activities has made the problem of nitrogen pollution in urban water bodies increasingly serious,and has gradually become a research hotspot.The nitrogen cycle in aquatic ecosystems is mainly driven by biological processes,in which denitrifying bacteria play a key role.Studying the characteristics of denitrifying bacterial communities in urban landscape water bodies has important guiding significance for microbial remediation technology.The discovery of aerobic denitrifying bacteria makes it possible for nitrification and denitrification to be carried out simultaneously under aerobic conditions,which are of great significance for the remediation of microorganisms in natural aquatic ecosystems.In this study,high-throughput sequencing technology was used to diagnose the community structure and diversity of nirS denitrifying bacteria in six geographically distributed urban lake sediment,with a view to providing theoretical support for subsequent microbial water remediation.Based on ultrasonic pretreatment technology combined with traditional selective media screening methods,three highly efficient aerobic denitrifying bacteria consortia and one aerobic denitrifying bacterial strain were successfully isolated from different ecological environments in China.Subsequently,the performance of nitrogen and carbon removal was investigated,and carbon metabolic mcechanism were explored,these results will give new insights for understanding metabolic flux analysis of aerobicdenitrifying bacteria,and provide bacteria sources for water body microbial remediation engineering.The main results of this study are as follows:(1)The results of the community structure and diversity of nirS aerobic denitrifying bacteria from based on high-throughput sequencing technology showed that the dominant nirS denitrifying bacteria from six geographically distributed urban lake sediment was Proteobacteria.The dominant classes were?-proteobacteria and?-proteobacteria.Rhodobacteria have relatively high abundance in nirS denitrifying bacterial communities.The dominant order was Zoogloeaceae.The dominant genus mainly included Dechloromonas,Cupriavidus,Azoarcus and Thiobacillus.Meanwhile,the principal coordinate analysis(PCo A)showed that the composition of nirS denitrifying bacteria was affected by geographic location.(2)The screening results of high-efficiency aerobic denitrifying bacteria showed that 252 aerobic denitrifying bacterial consortia and 159 aerobic denitrifying bacterial strains were isolated from different aquatic ecological environments.The nitrate nitrogen removal efficiencies of aerobic denitrifying bacteria screened from different ecological environments were relatively high.65.48%of the bacteria had higher nitrate nitrogen removal efficiency than 80%,while 81.34%of the bacteria had total nitrogen removal efficiency lower than 80%.Wastewater treatment reactors and natural water sediments that have been artificially added with bacteria were more likely to screen out highly efficient aerobic denitrifying bacteria.Ultrasonic pretreatment technology can effectively increase the number of highly effective aerobic denitrifying bacteria.The optimal domestication time is 21 to 30 days.(3)Three Mix-CADB consortia exhibited excellent total organic carbon(TOC)removal and aerobic denitrification capacities.The TOC and nitrate removal efficiencies were higher than 93%and 98%.77%of nitrogen in mix-cultured D14 system was lost as gaseous products.Results of Biolog-ECO assay demonstrated that three communities displayed high carbon sources metabolic activity.The nirS gene sequencing and ecological network analysis revealed Pseudomonas stutzeri,Paracoccus sp.,and Paracoccus denitrificans were dominated in D14,X21 and CL communities,respectively.Co-existence of core species,and dynamics and interaction in communities drove the nutrient removal.Moreover,response surface methodology(RSM)displayed that the highest TN removal efficiency was 99.43%.(4)A newly strain LSL251 was isolated from a Yinmatu wetland and identified as Paracoccus thiophilus.Strain LSL251 simultaneously removed 94.79±0.20%of total organic carbon,98.78±0.11%of nitrate nitrogen,and 74.66±0.32%of nitrogen in the culture system was lost as gaseous N products.Moreover,the results of metabolic flux and ¹³C-stable isotopic labeling with metabolic flux analysis(¹³C-MFA)revealed that the primary intracellular carbon metabolic pathways were the Entner-Doudoroff(ED)pathway and the tricarboxylic acid(TCA)cycle.Electrons are primarily donated as direct electron donor-NADH through the TCA cycle.Furthermore,response surface methodology results displayed that the highest TN removal efficiency was up to 98.43%,where the optimal parameters were C/N ratio of 8.00,32.98?,50.18 rpm,and initial pH of 7.73.