Deciphering the Assembly Processes of the Key Ecological Assemblages of Microbial Communities in Thirteen Full-Scale Wastewater Treatment Plants

Abstract

Limited information is currently available on the assembly processes (deterministic vs. stochastic) shaping the compositions of key microbial communities in activated sludge (AS). The relative importance of deterministic and stochastic processes for key bacterial and archaeal assemblages (i.e., core-satellite and habitat generalist-specialist) in AS from 13 wastewater treatment plants in China was investigated using 16S rDNA amplicon sequencing. The results obtained indicated 1,388 and 369 core operational taxonomic units (OTUs), 1,038 and 1,683 satellite OTUs, 255 and 48 habitat generalist OTUs, and 192 and 111 habitat specialist OTUs for Bacteria and Archaea, respectively. The proportions of shared OTUs between core and habitat specialist communities were similar to or higher than those between core and habitat generalist communities, suggesting a stronger inter-linkage between the former two groups. Deterministic processes, indicated by abundance-based β-null models, were responsible for shaping core communities, in which NH₄-N, OrgC/OrgN, Cr, and Ni were the main controlling factors. In contrast, satellite communities were predominantly influenced by stochastic processes. Moreover, we found that deterministic and stochastic processes were mainly responsible for shaping the assembly of habitat specialists and generalists, respectively. However, the influence of deterministic factors on habitat specialists remains unclear. The present study provides novel insights into the assembly mechanisms of AS microbial communities.

Keywords: activated sludge; amplicon sequencing; community assembly; core and satellite; habitat generalist and specialist; microbial community.

Fig. 1

Abundance-occupancy relationship of bacterial (A, C) and archaeal (B, D) taxa in 13 WWTPs. In Fig. 1A and B, dark grey and grey colors represent core and satellite taxa, respectively, and the red lines represent the linear regression model fit to the species abundance distribution. The coefficients of linear models were shown in Fig. 1A–D. In Fig. 1C and D, red and blue colors represent generalist and specialist taxa, respectively.

Fig. 2

Venn diagram showing the number of bacterial (A) and archaeal (B) OTUs shared among four ecological groups (i.e. core, satellite, generalist, and specialist). Values in brackets represent the percentages of total OTUs.

Fig. 3

Taxonomic compositions of bacterial (A) and archaeal (B) taxa in core, satellite, habitat generalist, and habitat specialist groups. Only phyla or classes belonging to Proteobacteria accounting for more than 0.5% of the total sequences in each ecological group were shown for Bacteria. Only families accounting for more than 0.5% of the total sequences in each ecological group were shown for Archaea.

Fig. 4

PCoA ordination with the Bray-Curtis dissimilarity matrix of four ecological groups of bacterial (A–D) and archaeal (E–H) communities in WWTP. Fig. 4A and E, B and F, C and G, and D and H represent core, satellite, habitat generalist and habitat specialist groups, respectively.

Fig. 5

Relative importance of niche and neutral processes, which were assessed using deviations from abundance-based β-null models (Bray-Curtis dissimilarity), on the assembly of different ecological groups of bacterial and archaeal communities in 13 WWTPs.