Bacterial generalists in earthworm gut had stronger environmental adaptation potential and higher network vulnerability under antimony stress

Abstract

Deciphering how communities assemble in gut bacteria in response to antimony (Sb) stress is beneficial to better understand the detoxification mechanism of earthworms to Sb, which is crucial for comprehensive understanding in situ remediation of Sb contaminated soil. However, little is known about the assembly processes of generalists and specialists in earthworm gut, particularly with their environmental adaptation potential. Herein, we conducted a 4-week exposure experiment, and analyzed the evolutionary characteristics, community assembly processes and network stability of generalists and specialists in earthworm (Eisenia fetida) gut and soil taxa. The results demonstrated that the taxonomic distance and phylogenetic distance of generalists were significantly lower than those of specialists (P < 0.001) both in earthworm gut and in soil. The environmental thresholds of generalists in earthworm gut were generally higher than those in soil, while the environmental thresholds of specialists in earthworm gut were lower. Generalists had stronger phylogenetic signals than specialists did both in earthworm gut and in soil. The binary-state speciation and extinction model revealed that the speciation rates of generalists and specialists in earthworm gut were 7.67 and 0.96, which increased by 7.42 and decreased by 1.72 compared with the corresponding rates in soil, respectively. Generalists and specialists had higher evolutionary efficiency in earthworm gut than in soil. The null model analysis exhibited that the stochastic processes of generalists and specialists in earthworm gut were mainly determined by undominated part (98.48% and 86.36%, respectively), while those in soil were primarily determined by homogenizing dispersal (80.30%) and dispersal limitation (78.79%), respectively. The network analysis displayed that the nodes and edges of the global network and the specialist sub-networks in soil were more than those in earthworm gut, while the nodes and edges of the generalist sub-networks in soil were less than those in earthworm gut. The sub-networks of generalists and specialists had stronger robustness at low Sb concentration, and generalist sub-network was more vulnerable than specialist sub-network. These results make up for the knowledge gaps of the speciation, evolution and maintenance mechanism of bacterial communities in earthworm gut under Sb stress, and provide new evidence for formulating bioremediation strategies of Sb contaminated soil.