How did the bacterial community respond to the level of urbanization along the Yangtze River?

Bacterial communities in the sediment of the Yangtze River influenced by rapid urbanization have thus far been under-investigated despite the importance of microorganisms as mass transporters. Here, the response patterns of the bacterial community along the Yangtze River to different levels of urbanization were generated using 16S rRNA Miseq sequencing. The results reveal that economic aspects have made the largest contribution (41.8%) to the urbanization along the Yangtze River. A clear declining tendency in the abundance of Chloroflexi and Acidobacteria and a significant increase in the abundance of Bacteroidetes were observed with an elevated urbanization level gradient. Bacterial diversity showed a negative relevance (P < 0.01) to the demographic, economic and social urbanization index. Per capita gross domestic product (GDP) (PCGDP) and the GDP of tertiary industry (GDP3) exhibited significantly (P < 0.05) negative correlations with the bacterial diversity, while a positive relationship between the pH and α-diversity (P < 0.05) was observed. Redundancy analysis revealed that PCGDP was significantly correlated (13.9%, P < 0.01) with the overall bacterial compositions, followed by temperature (10.8%, P < 0.01) and GDP3 (8.4%, P < 0.05). Meanwhile, the GDP3 (35.9%), the ratio of total nitrogen and total phosphorus (N/P) (12.9%) and the PCGDP (8.8%) were revealed to be most significantly related to the metabolic bacteria (P < 0.05). The metabolic functions of the bacteria related to the N-cycle and S-cycle were significant in the sediment of the Yangtze River. The variations of the bacterial community and metabolic function responding to the rapid urbanization were related to the economic development via the influence of the 'mass effect'. In brief, the tertiary industry was significantly correlated with the variations in the composition of the metabolic community and the variations in the overall bacteria were both related to the tertiary and secondary industry.