Abundances And Community Structure Of Sedimendenitrifying Bacteria In Five Typical Habitats Of Xiangshan Bay

Nitrogen pollution and coastal eutrophication is one of the major environmental problems facing the global ocean.With the aggravation of human activities,the red tide caused by the increase of nitrogen concentration is becoming more and more obvious.Denitrification,as an important part of nitrogen cycle,can reduce the free NO₃^-to gaseous N₂,which can effectively remove the marine nitrogen and alleviate the problem of marine nitrogen pollution.Therefore,denitrification plays an important role in offshore environmental governance and nitrogen global cycle.Denitrifying bacteria,as an important biological group involved in denitrification,have been paid more and more attention.Quantitative study on the abundance of denitrifying bacteria in sediment and characterization of its community structure further explore the important environmental factors affecting its community,which is of great significance to clarify the role of denitrifying microbial community in the global cycle of nitrogen in the nearshore.In order to further explore its role in nitrogen cycle and global climate change to provide theoretical support.Xiangshan Bay,located in the coastal area of North Central Zhejiang Province,is a semi closed long and narrow bay.In recent decades,due to the increase of land-based input and aquaculture activities,the water eutrophication in Xiangshan Bay waters has intensified.In this study,sediment samples from 5 typical habitats?oyster culture area or,kelp culture area SA,natural reef area IR,artificial reef area AR and control area CA?and oyster culture area and surrounding control area of Xiangshan Bay in March 2019were collected to study the abundance and community structure of denitrifying bacteria in Xiangshan Bay sediment.The main results of this study are as follows:1.Abundance and community structure of denitrifying bacteria in five typical habitats of Xiangshan Bay.?1?The average abundance of nirK type denitrifying bacteria was 2.68×10⁷copies/g,and that of nirS type denitrifying bacteria was 7.33×10⁹ copies/g.There was no significant difference?P>0.05?in the abundance of nirK type denitrifying bacteria among the five habitats in Xiangshan Bay,but the abundance of nirS type denitrifying bacteria was significantly different from that in other areas?P<0.05?,and the order of abundance was AR<OR=SA=IR=CA;the order of abundance of different types of denitrifying bacteria in each habitat was nirS type>nirK type?P<0.05?.?2?RDA analysis showed that TOC significantly affected the community of nirK and nirS type denitrifying bacteria.?P<0.05?,but there was no significant correlation between physical and chemical factors and nirS type denitrifying bacteria community?P>0.05?.There was no significant difference in ORP,water content and DIN among the five habitats?P>0.05?,while TOC and TON were significantly different among the five habitat types?P<0.05?.The TOC size of sediment was IR>SA=OR>AR=CA,and the order of TON size was IR=OR>SA=AR=CA.?3?Based on NMDS and anosim,there were significant differences between the five typical habitats in Xiangshan bay.The community of nirK type denitrifying bacteria in AR was significantly different from the other four habitats?Global R=0.581,P<0.001?;the community structure of nirS type denitrifying bacteria in AR was significantly different from that in OR,IR and CA?Global R=0.447,P=0.002?.?4?Phylogenetic analysis showed that the main groups of nirK type denitrifying bacteria in the sediments of five habitats in Xiangshan Bay were rhodobacteraceae,mabikibacter,alteromonadales and B cluster of non culturable groups.The dominant groups of nirS type denitrifiers are thiotrichales and rhodospirillales.It was found that most of the nirK and nirS sequences in the five habitats of Xiangshan Bay and the most similar sequences in Gen Bank were derived from similar environments such as estuaries and bays?Xiangshan Bay coastal sediments,Jiulong River Sediments and East China Sea sediments?.However,the sequence similarity with the known pure culture denitrifying bacteria is not high,which belongs to the non culturable group,indicating that there are a large number of novel denitrifying groups in Xiangshan Bay sediment,which has a high research significance.This study revealed that there are high abundance of nirS and nirK type denitrifying bacteria in the sediments of five typical habitats in Xiangshan Bay,and the AR abundance is the lowest compared with other four typical habitats,and the community structure is also significantly different,with obvious regional interval.2.Study on the influence of oyster culture on denitrifying bacteria community of marine sediment in Xiangshan BayIn this study,the abundance and community structure of denitrifying bacteria in the sediments of Xiangshan Bay oyster culture area and control area were determined by high-throughput sequencing and q PCR technology,and the correlation between environmental factors and denitrifying bacteria was analyzedfluence of oyster culture on denitrifying bacteria community of marine sediment in Xiangshan Bay.?1?In November 2018,the abundance of denitrifying bacteria in the sediments of oyster farming area and surrounding control area was explored.It was found that the average abundance of nirK type denitrifying bacteria in oyster area was 1.52×10⁷copies/g,and that in the control area was 1.54×10⁷ copies/g.The average abundance of nirS type denitrifying bacteria was 4.79×10⁹ copies/g in oyster area and 4.85×10⁹copies/g in control area.There was no significant difference in the abundance of denitrifying bacteria between the oyster culture area and the control area?P>0.05?.The abundance of nirS type denitrifying bacteria was significantly higher than that of nirK in each habitat.?2?RDA analysis showed that there was no significant correlation?P>0.05?between environmental factors and the community of denitrifying bacteria in the sediment of nirK type and nirS.There was no significant difference?P>0.05?in water content,ORP,TOC,and DIN between the control area and oyster area.?3?The results of NMDS showed that there was no significant difference between the two habitats?P>0.05?.Xiangshan Bay sediment environment.