Vertical Distribution Of Microbiol Community Structure In Lake Honghu Sediment

As a typical shallow lake of the middle and upper reaches of the Yangtze River, Lake Honghu is seriously affected by the Yangtze River. In this study, a 72 cm sediment core was obtained to investigate the vertical distribution of microbial community structure by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA- versus reversely transcribed 16S rRNA and internal transcribed spacer (ITS). The mainly physical and chemical properties of the sediment had been measured. The results revealed that the pH value, moisture and total P (TP) concentrations had no significant change with depth. While the total C (TC), total organic C (TOC) and total N (TN) concentrations peaked at 20 cm-25 cm. The bacterial and archaeal community structure changed significantly with depth. DGGE profiles of them showed that 16S rRNA-based DGGE band pattern was very similar to that of 16S rDNA, indicating that the active and present-day groups were dominant in the sediment. The dendrogram showed a significant difference between the upper (2 cm-32 cm) and lower layers (32 cm-72 cm). Shannon-Weaver index (H') of bacterial DGGE was slightly decreased at 2 cm-32 cm and then fluctuant below 32 cm. While the H' of archaeal DGGE was just opposite. Fungal DGGE bands had some difference between layers of 2 cm-14 cm and 14 cm-72 cm, the H' fluctuated at different depths. Cluster analysis showed that the upper 2 cm-18 cm clustered together, and the 18 cm-72 cm also clustered together with different subclasses.Phylogenetic analysis of microbial communities showed that the bacterial communities were primarily related to Proteobacteria, Acidobacteria, Actinobacteria, Deferribacteres, Firmicutes and Verrucomicrobia. The number of Betaproteobacteria was largest accounting for 44.2% of the total groups. The archaeal communities could be divided into Crenarchaeota and Euryarchaeaota, all of them were uncultured groups or clones. Fungal communities consisted of Ascomycota and Basidiomycota. The Ascomycota, which accounted for 70% of the total groups, dominated in the sediment. Ascomycota could be divided into two groups of Saccharomycotina and Pezizomycotina. Basidiomycota included Heterobasidiomycetes, Ustilaginomycetes and unclassified Basidiomycota.In conclusion, the active and present-day bacteria and archaea were dominant in the sediment. The bacterial and archaeal community structure changed drastically with depth, the fungal diversity also had some change with depth. The microbial diversity was mainly related to depth. Moreover, the archaeal diversity was significantly positively correlated with the nutrients TC, TOC and TN and the moisture. The bacterial diversity of rDNA level was mainly positively correlated with the moisture and TP, while the rRNA level diversity was negatively correlated with the pH value. The fungal diversity was mainly related to depth rather than the physical and chemical properties of the sediments.