Heterogeneity of interactions of microbial communities in regions of Taihu Lake with different nutrient loadings: A network analysis

Abstract

To investigate the differences in the interactions of microbial communities in two regions in Taihu Lake with different nutrient loadings [Meiliang Bay (MLB) and Xukou Bay (XKB)], water samples were collected and both intra- and inter-kingdom microbial community interactions were examined with network analysis. It is demonstrated that all of the bacterioplankton, microeukaryotes and inter-kingdom communities networks in Taihu Lake were non-random. For the networks of bacterioplankton and inter-kingdom community in XKB, higher clustering coefficient and average degree but lower average path length indexes were observed, indicating the nodes in XKB were more clustered and closely connected with plenty edges than those of MLB. The bacterioplankton and inter-kingdom networks were considerably larger and more complex with more module hubs and connectors in XKB compared with those of MLB, whereas the microeukaryotes networks were comparable and had no module hubs or connectors in the two lake zones. The phyla of Acidobacteria, Cyanobacteria and Planctomycetes maintained greater cooperation with other phyla in XKB, rather than competition. The relationships between microbial communities and environmental factors in MLB were weaker. Compared with the microbial community networks of XKB, less modules in networks of MLB were significantly correlated with total phosphorous and total nitrogen.

Figure 1

Species-species association network divided by module in MLB and XKB for bacterioplankton and microeukaryotes. Only correlations between species that were statistically significant (P < 0.01, Q-value < 0.05) and strong (r ≥ 0.9) were shown. Red solid line means positive correlation and black lines mean negative correlation. Different microbial phyla were represented with different colors and the number on each node means the number of OTUs clustered at 97% similarity. The circles consist of some nodes mean modules. Figure (a) and (b) represent bacterioplankton networks from MLB and XKB, respectively. Figure (c) and (d) represent microeukaryotes networks from MLB and XKB, respectively. Modules including less than 4 nodes are removed or abridged for concision.

Figure 2

Zi-Pi plot showing the distribution of OTUs based on their topological roles. Each symbol represents an OTU in MLB (red) or XKB (blue) for bacterioplankton (a) microeukaryotes (b) and inter-kingdom (c). The topological role of each OTU was determined according to the scatter plot of within-module connectivity (Zi) and among-module connectivity (Pi). The module hubs and connectors are labeled with numbers.

Figure 3

Environmental eigengene networks uncovered relationships between modules (based on the MLB (a) and XKB (b) network) and environmental variables for bacterioplankton. Only correlations that are statistically significant (P < 0.05) are shown. The line thickness is proportional to the absolute value of the Spearman’s correlation coefficient. Node labels stand for environmental variables or the eigengene of a module. The red solid line signifies a positive correlation, and the black line signifies a negative correlation. Environmental variables: TN, total nitrogen; TP, total phosphorus; NH₄, ammonia nitrogen; NO₂, nitrite; DOC, dissolved organic carbon.