(A) The co-occurrence network interactions of bacteria released from landfill sites (n=20; Spearman’s |R|>0.6, P<0.05) correlation. The nodes represented unique OTU in the data sets. The size of each node is proportional to the relative abundance (>0.1% in abundance in all samples); topological characteristics were characterized by igraph package in R. The nodes were networked in an efficient approach, which was identified as the type of “small-world”, which means geodesic (i.e., shortest-path) distance between nodes (OTU) increases sufficiently slowly as a function of the number of nodes in the network. (B) In this network, the selection of keystone species in the network was based on the high degree and low betweenness, which was further validated by their impacts on the changes in smallworldness index (>1.0) of the bacterial community in landfill leachates. The removal of keystone nodes (degree >65, betweenness <1000) resulted in significantly more pronounced changes in the bacterial community structure (P<0.01). The raw data were uploaded in NCBI and the accession number was provided in the Supplementary information.