| Nitrogen is a key element of marine life.It controls most of the primary productivity of the global oceans and therefore plays a key role in the carbon cycle of the ocean.The marine nitrogen cycle is mainly driven by various biogeochemical transformations mediated by microorganisms,mainly including nitrification,denitrification,and anammox.In recent years,Zhanjiang Bay,which is in a subtropical monsoon climate,has experienced rapid economic development,increased input of inorganic nitrogen concentrations,and coastal areas nitrogen pollution has become more serious.Therefore,a deep understanding of how nitrification,denitrification and anammox microorganisms play roles in the nitrogen cycle,and the relationship between them,is of great significance for understanding the status of the tropical coastal environment and the treatment of coastal nitrogen pollution.In this study,fluorescent quantitative PCR(q PCR),high-throughput sequencing were used to research temporal and spatial distribution characteristics of the abundance and diversity of nitrifiers(AOA,?-AOB,NOB),denitrification and anammox bacteria,and environmental factors affecting community structure in Zhanjiang Bay.At the seme time,through enrichment culture,AOA and ?-AOB were separated and purified to study the phylogenetic and physiological characteristics of pure strains.The main findings are as follows:(1).In the surface sediments of Zhanjiang Bay,the abundances of nir S,nir K,nos Z-type denitrifying bacteria and anammox bacteria all showed obvious seasonal changes,and the average abundance of nir S-type denitrifying bacteria was tends to increase first and then decrease.Continuous observation that the changes of nitrifiers(AOA,?-AOB,NOB)in Zhanjiang Bay water.The results showed that the abundance of nitrifying microorganisms showed obvious seasonal changes.It was found in three diurnal observations that NOB(Nitrospira,Nitrospina)16S r RNA gene copies showed obvious diurnal changes,while the AOA,?-AOB amo A gene copies was almost unchanged.(2).Phylogenetic analysis showed that there are some widely distributed denitrifying bacteria in the sediments of Zhanjiang Bay,but there are also some novel nir K and nos Z denitrifying bacteria.For anammox bacteria,it mainly belongs to the Planctomycetes and Candidatus scalindua,and a new branch of the anammox bacteria inhabited in Zhanjiang Bay that are not found elsewhere.By using Nitrospira nxr B as a functional and phylogenetic marker,69 species-level OTUs were detected from 4 water samples in Zhanjiang Bay,97% of which are new OTUs that are not related to any of the Nitrospira genus previously described,revealing the unrecognized diversity of coastal Nitrospira;and this study found that the sequences of the first 2 OTUs including OTU2 and OTU7 accounted for 48.7% and 32% of the total Nitrospira in July and September,respectively,and a unique cluster formed in the phylogenetic tree and was named Nitrospira ZJW lineage.(3).Correlation analysis showed that p H,nitrite,salinity,and temperature significantly affected the community of denitrifying bacteria in the sediments of Zhanjiang Bay;and nitrite significantly affected the communities of Nitrospina,AOA,and ?-AOB in Zhanjiang Bay water,but Nitrospira was regulated by p H and salinity.At the same time,the ratio of Nitrospira : Nitrospina 16 S r RNA gene numbers was significantly negatively correlated with nitrate,and the ratio of AOA : ?-AOB amo A gene numbers was significantly negatively correlated with ammonia and temperature.(4).By laboratory enrichment culture and isolation of AOA and ?-AOB results showed that in the enriched AOA samples at 6 sites,the relative abundance of Nitrosocosmicus and Nitrosopumilus was the highest and some novel AOA were found;isolated ?-AOB belongs to salt-tolerant bacteria,its maximum ammonia-resistant concentration is less than 240 m M,and cyanate may have a significant inhibitory effect on it. |
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