Microbial Community Characteristics In The Water Column Contaminated With Ammonia-nitrogen Along The Dongjiang River

With the rapid development of social economy, reactive nitrogen released into theenvironment is increasing, which results in the elevated nitrogen in rivers, subsequentlyinterferes with the balance of the nitrogen budget, even attribute to the eutrophication andbloom in a large area of red tide in coastal region. The Dongjiang river, an important rawwater for drinking water supply in South China, is contaminated by high level ammonia in thewater, and the water quality contamination is closely relate with the economic development.Due to the polluted river is not good for the economic development and threaten to humanhealth, therefore, wide public concern is focusing on the problems that how to speed up themicrobial mediated nitrogen cycling rate for effectively reducing the nitrogen level and forrelieving the risk of nitrogen pollution in the river. To exploit the solution to the nitrogencontamination, the culture-independent molecular microbial ecology methods andmultivariate statistical analysis methods were combined to study: the composition and theirdynamic changes of microbial community over spatio-temporal scale, the correlation betweenenvironmental factors and microbial community, the response of microbial communities tothe nitrogen concentration in the river and the key factors affect the activity of microbialcommunity structure.The sequences analysis of the clone library for bacterial16S rRNA genes showed that ahigh diversity of bacterioplankton community in the Dongjiang River. Five representativephyla, including Proteobacteria (Alphaproteobacteria, Betaproteobacteria andGammaproteobacteria), Actinobacteria, Bacteriodetes, Verrucomicrobia and candidatedivision TM7, were identified in sampling sites. Most of the sequences (85.0%) wereaffiliated with the phylum of Proteobacteria, and the Betaproteobacteria was the dominantsub-phylum. and the most abundant family was Comamonadaceae with the range from32.0%to46.7%in the libraries. Most sequences (58.9%of the total) belong to39genera, and themost commonly found species were related to the genera Curvibacter, Hydrogenophaga andPolynucleobacter. The canonical correspondence analysis (CCA) ordinations of the microbialpatterns and environmental variables demonstrated that N nutrient (nitrateand ammonia) wasstrongly correlated with most bacterial communities in the Dongjiang River.Denaturing gradient gel electrophoresis (DGGE) technique was applied to monitoringthe dynamic changes of microbial communities on the spatio-temporal scale. DGGE profilesand their digital information revealed the diversity and the variability of band patternsbetween the sampling sites in wet season and dry season. Sequences retrieved from gels evidenced the complexity of microbial community, with the dominance of phylumproteobacteria. Non-metric multidimensional scaling (MDS) revealed clear seasonalseparation based on the samples from different seasons; and CCA ordination plots revealedthat nitrate and pH were the main factors affecting the composition of bacterioplanktoncommunity. In addition, there were no significant difference between the DGGE techniqueand clone library construction method, considering the laborious and time-consumingcharacteristics of clone library construction method DGGE technique may be a more rapidand straightforward alternative choice for tracking genotypic community changes and cangive a good microbial overview with medium phylogenetic resolution in the Dongjiang River.Ammonia-oxidizing archaea (AOA) was found firstly in the Dongjiang River throughthe molecular determination of the amoA gene, which codes the catalytic alpha-subunit ofammonia monooxygenase catalyzing the first rate-limiting step in the nitrogen cycle.Phylogenetic analysis of archaeal amoA gene revealed that AOAin the Dongjiang River wasaffiliated with Crenarchaeota, and showed lower similarity to sequences from marineenvironments and soil habitats. AOAs were divided into three clusters, and the freshwatercluster1(88%) was predominant over the other two clusters in whole basin. The AOBs weregrouped in Nitrosomonas and Nitrosospira, and Nitrosomonas was predominated overNitrosospira. The results of quantitative PCR analysis illustrated thatArchaeal amoA genesoutnumbered bacterial amoA genes in the whole basin, and the ratio ofAOA/AOB wasnegatively correlated with the ammonia concentration. These results suggested that AOAswere well adapted to the low ammonia environment and contributed to the nitrogen cycling ina relative low-ammonia habitat.To our knowledge, the molecular analysis of the microbial community composition andtheir response to environmental factors was first report in the Dongjiang River. This study wasproviding the fundamental scientific data for the further development and utilization ofmicrobial resources, for the water purification and health status monitoring in the DongjiangRiver. Furthermore, it is of significance in the control of the nitrogen contamination and themaintaining of the river ecosystem health in the future.