| Eutrophication of lakes,causing severe damages to aquatic ecosystems and threatening the safety of drinking water,is a serious issue of the environment in the world.Without external pollution source,the release of phosphorus in sediment is an important factor causing eutrophication of a lake.The current studies mainly focus on the microbial diversity and environmental factors in the process of shallow lake eutrophication.The compositions of microbial communities and their roles in the phosphorus cycles of sub-deep lakes have been rarely investigated.The Sancha Lake,studied in this paper,is located in the upper reaches of Jiangxi River,a tributary in Tuojiang River of the Yangtze River system.This lake serves as an important drinking water source for the Tianfu New Area of Chengdu City and is a sub-deep lake with internal pollution and eutrophication.With the Sancha Lake as the study object,the structure,diversity and abundance of microbial communities in water and sediment and their response mechanism to major environmental factors were systematically studied in this paper by high-throughput sequencing,fluorescence quantitative PCR,pure culture technique,indoor static simulation,bioinformatics,and so forth.The roles of microorganisms in the interfacial transfer and transformation processes of phosphorus between sediment and water were analyzed to explore the contribution of functional microorganisms to eutrophication of water and to shed light on the restoration and management of similar lakes undergoing eutrophication.The primary results are presented as follows:(1)The temporal and spatial variation characteristics of phosphorus compounds in the water and sediment of the Sancha Lake were verified.From the year of 2015 to 2017,the total phosphorus(TP)contents in the water body were in the range of 0.034 to 0.227 mg·L-1.The TP contents in the reservoir tail and bay area were higher,and those in spring and winter were higher.Dissolved total phosphorus(DTP)is an important component of TP,and DTP mainly consisted of dissolved orthophosphate(SRP).The temporal and spatial variation characteristics of DTP and SRP were similar to those of TP.The contents of SRP and TP in the water body were significantly positively correlated to the content of chlorophyll a(Chla)(p<0.01),indicating that phosphorus was the crucial determining nutrient for the primary productivity in the Sancha Lake.On the other hand,the TP contents in the sediment were in the range of 0.243to 3.774 mg·g-1,higher than those of similar lakes.The TP content in the original culture area was higher,and those in winter and autumn were higher.The phosphorus in the sediment mainly consisted of phosphorus hydrochloride(HCl-P),followed by organic phosphorus(OP),and the content of sodium-hydroxide-type phosphate(Na OH-P)was the lowest.The types of available phosphorus and their contribution to water phosphorus varied under the different temporal and spatial sampling conditions.The release of phosphorus from sediment was the internal pollution source in the Sancha Lake.(2)The structural composition,diversity and distribution characteristics of bacterial communities in the sediment of Sancha Lake during spring,summer,autumn and winter in the year of 2017 were probed by Miseq high-throughput sequencing technology based on the 16S r RNA gene.The results showed that the diversity of bacterial species in the sediment was high,and 9,325 OTUs acquired were acquired belonging to 64 phyla,259 classes and 1310 genera.Proteobacteria,Actinobacteria and Chloroflexi phyla were dominant.Metastats test results showed that the relative abundances of dominant phyla Actinobacteria and Chloroflexi and dominant genera hgc I?clade,Pseudomonas,Sulfuricurvum,Syntrophus,Dechloromonas,and Thiobacillus changed significantly against seasons(p<0.05).The results of non-metric multidimensional scale analysis(NMDS)and clustering analysis showed that the bacterial communities in sediment in spring and other seasons formed distinct characteristic groups.The groups of sediment sampled in spring aggregated,but those sampled in other seasons were mixed with each other.Pearson correlation and redundancy analysis(RDA)results showed that dissolved oxygen(DO),p H,temperature(T),phosphorus and total organic carbon(TOC)were the dominant environmental factors affecting the bacterial community structure in the sediment of the Sancha Lake.The linear regression analysis results showed that the relative abundances of dominant phyla(Actinobacteri and Cyanobacteria),dominant classes(Actinobacteria,Cyanobacteria,Flavobacteriia,Alphaproteobacteria,and Chloroplast)and dominant genera(hgc I?clade,Pseudomonas and Thiobacillus)were significantly positively correlated with the SRP content in the overlying water(p<0.05).However,the relative abundances of dominant phylum Chloroflexi and dominant class Deltaproteobacteria,were significantly negatively correlated with the SRP content in the overlying water(p<0.05).Therefore,the bacteria in sediment sensitively responded to phosphorus in the water,and the mechanism may be related to the phosphorus dissolving function of microorganisms.(3)The high-throughput sequencing analysis results showed that the diversity of the bacterial communities in the overlying water of the Sancha Lake during the spring and autumn of 2017 was high,and 9,557 OTUs were obtained,belonging to 55 phyla,64 classes and 732genera.Among them,Proteobacteria,Actinobacteria and Firmicutes were the dominant groups.Metastats test results showed that the same bacterial groups were observed in the overlying water during both seasons,but the difference was considerable(p<0.05).The relative abundances of dominant genera Pseudomonas and Bacillus in autumn were significantly higher than those in spring(p<0.01),respectively.This should be attributed to the response of the vigorously growing phytoplankton in autumn to the phosphorus deficient water environment.Principal component analysis(PCA)and clustering analysis results showed that two distinct cladistic groups of bacterial communities in the overlying water were formed during the spring and autumn.Pearson correlation and RDA analysis results showed that the distribution of bacterial communities in the overlying water of the Sancha Lake was mainly affected by phosphorus,permanganate index(CODMn),DO and p H.(4)The diversity and abundance of organophosphorus dissolving bacteria(OPB)and inorganophosphorus dissolving bacteria(IPB)in the sediment of Sancha Lake and their response to environmental factors were studied by high-throughput sequencing with the molecular markers of alkaline phosphatase(ALP)gene pho D and glucosidase(GDH)gene gcd.The results showed that the diversity of phosphorus dissolving bacteria was high.Pseudomonas,Streptomyces and Phaeobacter were the dominant genera of OPB.Rhizobiales,Burkholderiales and Pseudomonadales were the dominant orders of IPB.The distributions of OPB bacterial communities during spring and autumn were significantly different,but the spatial heterogeneity was not obvious.The IPB bacterial communities in the bay and inlet areas presented significant seasonal changes.The p H,DO and phosphorus in the overlying water and sediment were the critical factors influencing OPB and IPB bacterial communities in the sediment of the Sancha Lake.Fluorescent quantitative PCR analysis results showed that the copy number of OPB pho D gene in autumn was significantly greater than that in spring(p<0.05),and the copy number was positively correlated with the SRP content in the overlying water(p<0.05).On another hand,the copy number of IPB gcd gene in spring was greater than that in autumn,and the copy numbers in both seasons were significantly positively correlated with the SRP content in the overlying water(p<0.05).Therefore,the changes in community composition and absolute abundance of phosphorusdissolving bacteria containing pho D and gcd genes were coupled with the changes of SRP content in the overlying water.OPB and IPB may play an important role in the transport and transformation process of phosphorus at the sediment-water interface of the Sancha Lake.(5)A total of 82 bacterial strains with stable organic and inorganic phosphorus dissolving activities were isolated from the sediment of Sancha Lake by selective culture,and these strains were categorized by taxonomy.39 OPBs,including rare Acidovorax sp.SWWO1711,were assigned to 5 genera.43 IPBs,including rare Caryophanon tenue SWSI1715 and Rhodococcus aetherivorans SWSI178,were classified into other 9 genera.Strains SWSO1719,SWWO1721,SWSI1728,SWSI1734 and SWSI1719 were potential new types.The results of polyphasic taxonomy showed that SWWO1721,denoted by Spirosoma lacussanchae sp.nov.in this paper,should be a new potential species of Spirosoma genus.(6)The phosphorus dissolving characteristics of the strains isolated were studied by experiment with flasks and indoor static simulation experiment.Calcium phosphate could be dissolved by 43 IPB strains to release dissolved inorganic phosphate(DIP),and the p H of the culture medium was reduced.The phosphorus-releasing abilities of these strains were different,with phosphorus releasing amounts of 1.79 to 102.77 mg·L-1.The phosphorus dissolving characteristics were affected by the DIP content and p H.The DIP content was significantly negatively correlated with p H,and the release process was consistent with exponential functions.Lecithin could be dissolved by 39 OPB strains,with phosphorus releasing amounts of 0.47 to 70.91 mg·L-1,and their phosphorus dissolving characteristics were affected by the interaction between DIP content and ALP activity.The culture solution of most of the IPB strains could significantly promote the decomposition and release of HCL-P in the sediment(p<0.05).In contrast,the dosage of the culture media of some IPB strains could significantly facilitaed the transformation of organic phosphorus in the sediment into inorganic phosphorus(p<0.05).The phosphorus dissolving bacteria in the Sancha Lake played an important role in the release of phosphorus from sediment.In summary,the eutrophication in the Sancha Lake was related to the ecological functions of microorganisms in the overlying water and sediment during the phosphorus cycle.The sediment of the Sancha Lake was rich in phosphorus dissolving microorganisms,of which the structure and composition were closely related to environmental factors.These microorganisms played an important role in the transfer and transformation of phosphorus at the sediment-water interface,and contributed greatly to water eutrophication of the Sancha Lake. |
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