Community Structure Analysis Of Bacteria And Archaea In Sediments Of The Jiulong River Estuary And The Taiwan Strait

As an important component of the ecosystem,microbes play crucial roles in driving the geochemical cycle of elements,maintaining the stability of the ecosystem,and purifying the environment.The estuary is a unique geographical transition zone located at the confluence of rivers and oceans,which is considered as a natural testing ground for investigating the microbial community structure and diversity in a complex and changing environment.Meanwhile,the stability of ecosystem functioning can be largely affected by microbial functional diversity,and thus microbial diversity can also be used as an important biological indicator for assessing environmental quality of the estuary and coastal ecosystems.Therefore,it is of great importance to fully understand the microbial community structure and diversity and reveal their roles in the estuary and coastal environment.In the present study,the surface sediments were collected from the Jiulong River Estuary and djacent Taiwan Strait.Applying 16S r RNA gene high-throughput sequencing and quantitative PCR techniques,we systematically explored the community structure and diversity of bacteria and archaea and their ecological functions in the surface of sediments estuary and coastal environment.The results are as follows:1.The absolute abundance of bacteria and archaea was 1.5×10~7-1.3×10~9 copies/g(wet weight)and 3.0×10~6-4.7×10~7 copies/g(wet weight)in the surface sediments,respectively.Overall,the absolute abundance of archaea in each sample was 1-2 orders of magnitude less than that of bacteria.In the Jiulong River Estuary,the correlation analysis showed that the absolute abundance of bacteria and archaea was positively correlated with the nutrient content such as the ammonia nitrogen content and the total organic carbon content(TOC).In comparison,there was no significant correlation between the absolute abundance of bacteria and the measured environmental factors in the surface sediments of the Taiwan Strait,while the archaeal abundance had a significant negative correlation with the dissolved oxygen content(DO)of the bottom water.2.The diversity of bacteria and archaea in the Jiulong River Estuary had different trends along the salinity gradient.The diversity of bacteria showed an increasing trend with the increase of the salinity gradient,while the archaeal diversity in the high salinity area and the transition area was higher than that in the low salinity area.And the diversity difference of bacteria and archaea among the various regions of the Taiwan Strait was not significant.In terms of community composition,the bacterial and archaeal communities in the low salinity area from the Jiulong River Estuary was significantly different from the other areas.The dominant bacterial species in the low salinity area of the Jiulong River Estuary was Firmicutes,but the abundance of this species was very low in the transition area,the high salinity area and the Taiwan Strait.The dominant taxa in the transition area,the high salinity area and Taiwan Strait were Proteobacteria,followed by Chlaoroflexi and Actinobacteriota.The abundant archaea groups in the sediments of the Jiulong River Estuary and the Taiwan Strait include Crenarchaeota,Halobacterota,Euryarchaeota,Thermoplasmatota and Asgardarchaeota.Among them,the abundance of Crenarchaeota was relatively high in the transition area and high salinity area of the Jiulong River Estuary,while the abundance of Halobacterota and Euryarchaeota was relatively high in the low salinity area.The composition of the archaeal community in sediments of the Taiwan Strait was also slightly different in each region.The composition of the archaeal community in the X and Q areas was similar to the high salinity area fromthe Jiulong River Estuary,and the abundance of Crenarchaeota was relatively high(about 50%),followed by Halobacterota and Thermoplasmatota;but in P and M areas the abundance of Crenarchaeota was relatively high(accouting for 60-80%of archaea)compared to the X and Q areas,while the proportion of Thermoplasmata was relatively low.3.The redundancy analysis(RDA)and Mantel test revealed that different environmental factors that affected the community structures of bacteria and archaea in the surface sediments from the Jiulong River Estuary and the Taiwan Strait.The r value of the correlation between the environmental factors and the bacterial community structure in the Jiulong River Estuary was 0.612(p<0.001),and the r value of the correlation between the geographical distance and the bacterial community structure was 0.482(p<0.01);the r values of the correlation between the environmental factors and the geographical distance with the archaea community were 0.450(p<0.001)and0.417(p<0.01),respectively.These results indicated that both of the environmental factors and the geographic distance determined the community structures of bacteria and archaea in the Jiulong River Estuary,but the effects of environmental factors was much higher than the geographical distance.Salinity,total dissolved solids(TDS)and chlorophyll-a were the main environmental factors affecting the bacterial community structure in sediments of the Jiulong River Estuary,while DO,TDS,ammonia nitrogen content and salinity had significant influence on the archaea community in sediments of the Jiulong River Estuary.In comparison,the bacterial community structure in sediments of the Taiwan Strait was mainly affected by the environmental factors(r=0.289,p<0.01),while the distance attenuation effect caused by the geographical difference was not significant(p>0.05),and TN and TOC were the main environmental factors affecting the bacterial community structure.In addition,the community structure of archaea was mainly affected by the geographic distance(r=0.158,p<0.05)in sediments of the Taiwan Strait,and it was only significantly positively correlated with BGA-PE in environmental factors.