Bacterial diversity and community structure in the sediment of the middle and lower reaches of the Yellow River, the largest turbid river in the world

The characteristics of bacterial community in the sediment of the middle and lower reaches of the Yellow River, the largest turbid river in the world, were studied by using the 16S rRNA gene clone library technique. Sediment cores with 25 cm depth were collected from 5 sites along the river and each sediment core was sliced into 5 layers for phylogenetic analyses. For the 25 clone libraries, a total of 2496 16S rRNA gene sequences were obtained and selected for taxonomic analysis. Furthermore, 1353 distinct operational taxonomic units (at the 97 % identity level) were assigned, suggesting that a large number of bacterial taxa existed in the sediments of the Yellow River. The dominant bacterial groups in each sediment sample were affiliated with the subphyla Betaproteobacteria (mainly order Burkholderiales) and Gammaproteobacteria (mainly order Xanthomonadales), followed by Bacteroidetes, Acidobacteria, and Verrucomicrobia. Based on Shannon index values, bacterial diversity in Yellow River sediment was higher than that in other, less turbid rivers. Bacterial community compositions differed among the 5 sampling sites, due to differences in environmental variables. Redundancy analysis and Monte Carlo permutation test results demonstrated the significant effects of ammonium nitrogen and nitrate nitrogen concentrations on bacterial community structures (p < 0.05). Due to the high sediment concentration and high-frequency resuspension and deposition of sediment in the Yellow River, the bacterial community exhibited vertical variations but did not show a significant trend with depth in the sediment core samples.