Anthropogenic activities drive the microbial community and its function in urban river sediment

Understanding the dynamics of the structure and function of the microbial community in sediment across freshwater environments will help to predict how these ecosystems will change in response to anthropogenic activities. We compared the community structure and abundance of C, N and S transformation-related functional microorganisms along two rivers in south-eastern China that flow through three typical anthropogenic zones corresponding to agricultural, residential and industrial areas. Microbial indices were calculated based on the abundance of specific phyla and functional groups. Illumina sequencing of 16S rRNA amplicons revealed that the sediments at all of the tested sites were dominated by Proteobacteria (41.4-54.4 %), with notable differences among the communities from different functional zones. The abundances of the nifH (5.57 x 10(5)-8.27 x 10(5) copies ng(-1) DNA), nirK (4.79 x 10(4)-6.22 x 10(4) copies ng(-1) DNA) and pmoA (7.02 x 10(4)-9.29 x 10(4) copies ng(-1) DNA) genes in the industrial zone were significantly higher than in the residential and agricultural zones. The gene copy numbers from both ammonia-oxidising Archaea (AOA) and Bacteria (AOB) from the agricultural zone were significantly higher than in the residential and industrial zones. Functional microorganisms for methanogenesis, nitrification and denitrification and sulphate reduction showed significant correlations with petroleum, nitrogen and sulphide, respectively. The ratio of AOA/AOB amoA gene copy numbers in the agricultural zone was < 1.0, indicating that the river basin in the agricultural zone was at a higher eutrophic level. The ratios of Bacteroidetes, Gammaproteobacteria and Nitrospira/Betaproteobacteria (BGN/beta) for the industrial zone (2.03-3.51) were significantly higher than those for the other two zones, indicating lower water quality in the industrial zone. These findings suggest that fluctuations in the microbial community in river sediment might be impacted by different human activities. The results also demonstrate that AOA/AOB and BGN/beta ratios are potential indicators of water ecological quality.