Ecological Distribution Of N-DAMO Bacteria In Marine/Freshwater Ecosystems And Their Response To Microplastic Pollution Efficient

Nitrite-dependent anaerobic methane oxidation（N-DAMO）is the oxidation of methane（CH₄）to carbon dioxide（CO₂）using nitrite（NO₂^-）as an electron acceptor,and is a key link in the coupled carbon and nitrogen cycle,mediated to completion by NC10phylum bacteria.To date,although molecular evidence of N-DAMO bacteria in freshwater rivers（detection of N-DAMO bacterial sequences）has been reported,the distribution pattern of N-DAMO bacteria in freshwater river sediments is still poorly understood,and the distribution pattern in marine sediments has been rarely reported.As an emerging contaminant,microplastics are ubiquitous in water sediments.However,the effects of microplastics on sedimentary microorganisms and biogeochemical carbon and nitrogen cycles are not well understood.In this thesis,the ecology of N-DAMO bacteria was studied in marine and freshwater river systems in order to investigate the ecological distribution characteristics,the intensity of action of methane anaerobic oxidizing microorganisms in marine and freshwater ecosystems and their role in the carbon and nitrogen cycles,greenhouse gas emission reduction and nitrogen pollution remediation in marine and freshwater rivers.To assess whether microplastics affect the activity,abundance,diversity and community structure of N-DAMO bacteria in sediments,microscopic experiments were conducted using PVC microplastics on N-DAMO bacteria in sediments of two ecosystems.The main findings are as follows:1)Stable isotope activity tracing experiments detected N-DAMO bacterial activity in both marine and freshwater river systems with reaction rates ranging from 0.11 to0.41 nmol CO₂ g^-1（dry weight）d^-1 and 0.18 to 0.48 nmol CO₂ g^-1（dry weight）d^-1,respectively,indicating that N-DAMO is an important methane sink in both marine and freshwater river systems.It was found that there were no environmental factors significantly associated with the distribution of N-DAMO bacterial activity in the ocean,and that sediment pore water or overlying water nitrate-nitrogen and total inorganic nitrogen concentrations were the main environmental factors affecting the distribution of N-DAMO activity in freshwater rivers.2)The quantitative distribution characteristics of N-DAMO bacteria in both marine and freshwater river systems were investigated,and a large number of N-DAMO bacteria were distributed in both marine and freshwater river systems in the range of105～106 copies g^-1（dry weight）.It was found that sediment pore water or overlying water salinity was the main environmental factor affecting the population distribution of N-DAMO bacteria in the ocean,and sediment pore water or overlying water p H and nitrite nitrogen concentration were the main environmental factors affecting the population distribution of N-DAMO bacteria in freshwater rivers.3)The diversity and community structure of N-DAMO bacteria in marine and freshwater river systems were investigated,and the sequencing results showed that there were several branches with close affinity to Candidatus Methylomirabilis oxyfera in marine and freshwater river systems,and the population diversity level was high.In both ecosystems,Group A（the main functional microorganism of N-DAMO reaction）was the dominant N-DAMO bacterium.Correlation analysis showed that the concentration of nitrate and nitrogen in sediment pore water or overlying water had a significant effect on the community structure of N-DAMO bacteria in Yellow Sea sediment,and the p H of sediment pore water or overlying water had a significant effect on the community structure of N-DAMO bacteria in Yellow River sediment.4)Compared with the control sediments without microplastics,PVC microplastics enhanced the activity of N-DAMO bacteria in marine and freshwater river systems,suppressed the abundance of N-DAMO bacteria in marine and freshwater ecosystems,enhanced the 16S r RNA gene diversity of N-DAMO bacteria and changed the community structure of N-DAMO bacteria in marine and freshwater river systems.These results suggest that microplastics can influence carbon and nitrogen cycling processes in sediments and they may be organic carbon substrates for microbial communities.