Characteristics Of Microbial Community Structure And Sulfur Invasion Process In Seagrass Bed Of Weihai Lagoon

Seagrasses are large underwater angiosperm with the general characteristics of higher plants and can fully adapt to the marine environment.Seagrasses mostly grow in the subtidal to the intertidal zone,forming a unique seagrass bed ecosystem as one of the three typical marine ecosystems(i.e.,together with mangrove and coral reef ecosystems).Seagrasses represent high primary productivity in the world.Although seagrass beds cover only 0.2%of the seabed area,they store 10%of the world's annual marine organic carbon,making them an important "blue carbonSwan Lake is a typical seagrass bed in northern China,where Zostera marina and Zostera japonica were discovered in the early 1970s.Z.marina is the dominant seagrass species,estimated to cover approximately 2.0 km2,mainly growing in the middle of the lagoon.Z.japonica inhabits shallow water or intertidal zones Microorganisms are essential components of the seagrass bed ecosystem,playing important roles in material cycles and energy flows.Seagrass-associated microbial communities include populations of microbes within the rhizosphere and attached to seagrass leaves.They are unneglected parts in the biogeochemical cycle of seagrass beds.Microbiomes play multi-faceted roles in maintaining a healthy seagrass holobiont,and elucidating the fundamental host-microbe interactions can provide insights for seagrass bed restorationThe current thesis studied the molecular ecology of microorganism dynamics in the rhizosphere sediments of Z.marina and Z.japonica in the Swan Lake Nature Reserve,Shandong.High-throughput sequencing was applied to analyze:?)the microbial diversity of the sediment profiles of Z.marina,Z.japonica,and degradation areas,?)the differences in the seagrass-associated microbial communities at different growth stages,and ?)the effects of additional sulfur compounds,sulfur-oxidizing bacteria,and FeCl3 on the microbiome of seagrassThe main results were as follows1.The microbial community's distribution pattern changed with the sediment depth and whether the seagrass was covered or not.A pronounced shift from Proteobacteria-dominated upper layers to Chloroflexi and Crenarchaeota-dominated deep layers in all sediment cores was observed in the vertical direction Bathyarchaeia was more abundant in the degradation area,while Vibrionaceae,Sulfur ovum,and Lokiarchaeial were overrepresented at the seagrass bed area Sulfurovum,Vibrio,Photobacterium and Woeseia were identified as the shared key genus with the highest abundance in the seagrass rhizosphereMoreover,Pb,Cd,Cu,Zn,Mn were enriched to varying degrees(1.61-3.62 times)in the Z.marina rhizosphere,indicating the capacity of trace elements monitoring.Vibrionaceae was abundant in the rhizosphere of Z.marina and Z.japonica,with the proportions reached 84.45%and 63.89%,respectively.It is speculated that the macrobenthic species near the seagrass caused the enrichment of Vibrio spp.Excessive shellfish farming can lead to an unhealthy microbiome in seagrass,resulting in an increased risk of seagrass bed degradation2.Microbial community structure varies significantly in different stages of seagrass growth.At the maturation stage of seagrass,Propionigenium was significantly enriched in the roots of Z.marina and Z.japonica,with a relative abundance of 11.58%and 14.26%,respectively.In the seedling stage of seagrass,Desulfobulbaceae was enriched at the seagrass roots(Z.marina:2.299%;Z.japonica 4.092%).During the decline stage of seagrass,the relative abundance of Sulfurovum was higher in the rhizosphere(Z.marina:5.624%;Z.japonica:3.749%).The microbial community structure of the seagrass bed had noticeable rhizosphere effects;the enriched microorganism species were the same in the rhizosphere of Z.marina and Z.japonica,indicating that the microbial community structure in the same region was not host-specificThe nMDS analysis and multivariate variance analysis showed that the interpretation of samples during seagrass growth was the largest(R2=0.20335,p=0.002).Environmental factors on the microbiome structure interpretation were in the second place.The sample interpretation was the lowest in groups with seagrass colonization(R2=0.07416,p=0.548),indicating that the seagrass microbiome structure was more obviously affected by the seagrass growth period3.Compared with the rhizosphere microorganisms,the phyllosphere microorganisms were more sensitive to the changes in different habitats of seagrass.Z.marina is dominant in low to subtidal areas.Z.japonica usually colonizes mid-to-low intertidal mudflats,with high irradiance,temperature fluctuations,and desiccation Although Proteobacteria and Firmicutes were the main microorganisms in both Z.marina and Z.japonica,there was a significant difference in proportion.The Z.marina phyllosphere microbiota was dominated by Proteobacteria(59.4%)and Firmicutes(9.27%).However,the Z.japonica phyllosphere microbiota consisted of 10.4%Proteobacteria and 80.1%Firmicutes,respectively.Exiguobacterium aurantiacum and Bacillus aryabhattai increased from 1.72%and 7.32%in the Z.marina phyllosphere samples with a relative abundance of 56.9%and 22.4%in the Z.japonica phyllosphere samples,respectively.Both strains can adapt to extreme conditions with plant growth-promoting potentials,such as high UV,drought,and high temperature.These findings were consistent with the habitat conditions of Z.japonica leaves4.A sulfur-oxidizing bacterium was screened from the Weihai Swan Lake sediment and identified as Hydrogenovibrio marinus ODH-3.ODH-3 was a chemotrophication sulfur oxidizing bacteria through experiments and gene sketch analysis,with a G+C content of 63.798%,with a complete SOX system gene.Besides,ODH-3 had NarGHI,NirK,and NorBC genes,which can transform nitrate nitrogen ODH-3 was mixotrophic with carbon sequestration-related genes and,which can use both inorganic and organic carbon as carbon sources.The optimal pH value for the oxidation of sodium thiosulfate was 6.5,and the optimal salinity was 10 g/L.When ODH-3 was immobilized with zeolite,its oxidation efficiency was significantly increased,and it was able to withstand higher pH and salinity changesA microcosm system was constructed to simulate seagrass invasion under sulfide by collecting samples of Z.japonica and its sediments from the Weihai Swan Lake The changes of microbial community structure during the invasion of seagrass by sulfide and the promoting effects of iron or sulfur-oxidizing bacteria on seagrass resistance to sulfide were comprehensively analyzed.The experimental results showed that(1)the chlorophyll content decreased most obviously after the first addition of sulfide.At the end of the microcosm experiment,the chlorophyll content in the FE group remained at a high level.In contrast,the chlorophyll content in the SOB group did not change significantly,indicating that the addition of FeCl3 and sulfur-oxidizing bacteria could help seagrass resist the invasion of sulfide and the exogenous strains did not cause harm to seagrass.(2)On day 0,the sulfur content of seagrass leaves was similar,while on day 5,the sulfur content of seagrass leaves in the SOB group and FE group decreased significantly.On the 10th day,the sulfur content in leaves of the SOB group continued to decrease,while those in the FE group increased sharply.On the 15th day,the sulfur content of seagrass leaves in the SOB group increased to 0.666%,which was similar to that in the Blank group.The sulfur content in seagrass leaves in the control group was the highest,which was 0.962%The results indicated that FeCl3 can relieve the intrusion pressure of sulfide in a short time.The added sulfur-oxidizing bacteria could resist the invasion of sulfur compounds within ten days,and the effect was more evident than that of FeCl3.(3)The relative abundance of microbial community structure in microcosmic sediments at the family level was Desulfocapsaceae,Pirellulaceae,Flavobacteriaceae,Desulfosarcinaceae from high to low.Desulfocapsaceae was the typical sulfate-reducing bacterium in the seagrass rhizosphere with the highest relative abundance,while Sulfurovum was the sulfur-oxidizing bacterium with higher relative abundance.The functional genes analysis showed that acsE,dsr,mct,dsrA,acsA were in high abundance.