Metagenomics combined with metabolomics reveals the effect of Enterobacter sp. inoculation on the rhizosphere microenvironment of Bidens pilosa L. in heavy metal contaminated soil.

Metagenomics analysis was performed to determine the effects of Enterobacter sp. FM-1 (FM-1) on key genera as well as functional genes in the rhizosphere of Bidens pilosa L. (B. pilosa L.). Moreover, metabolomics was used to reveal the differences among rhizosphere metabolites after FM-1 inoculation. FM-1 inoculation significantly increased the activity of enzymes associated with the carbon cycle in soil; among them, invertase activity increased by 5.52 units compared to a control. Specifically, the relative abundance of beneficial genera increased significantly, such as Lysobacter (0.45-2.58 unit increase) in low-contamination soils (LC) and Pseudomonas (31.17-45.99 unit increase) in high-contamination soils (HC). Comparison of different transformation processes of the C cycle revealed that inoculation of FM-1 increased the abundance of functional genes related to the carbon cycle in LC soil. In contrast, the nitrogen cycling pathway was significantly elevated in both the LC and HC soils. FM-1 inoculation reduced HM resistance gene abundance in the rhizosphere soil of B. pilosa L. in the LC soil. Moreover, FM-1 and B. pilosa L. interactions promoted the secretion of rhizosphere metabolites, in which lipids and amino acids played important roles in the phytoremediation process. Overall, we explored the rhizosphere effects induced by plantmicrobe interactions, providing new insights into the functional microbes and rhizosphere metabolites involved in phytoremediation.

Insight into the roles of soluble, loosely bound and tightly bound extracellular polymeric substances produced by Enterobacter sp. in the Cd2+ and Pb2+ biosorption process: Characterization and mechanism.

Extracellular polymeric substances (EPSs) are macromolecular polymers formed by metabolic secretion, and they have great potential for removing heavy metal (HM) ions from the aquatic phase. In this study, the contributions of soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs) and tightly bound EPSs (TB-EPSs) secreted by Enterobacter sp. to Cd2+ and Pb2+ adsorption were analyzed. The results indicated that in a solution containing both Cd2+ and Pb2+, pH= 6.0 was best suited for the adsorption process, and adsorption equilibrium was reached in approximately 120 min. Moreover, the mechanism for adsorption of Cd2+ and Pb2+ by the different layers of EPSs involved spontaneous chemical processes. However, Cd2+ adsorption by the three layers of the EPSs was an exothermic process (∆H0 <0), but Pb2+ adsorption by the three layers of the EPSs was an endothermic process (∆H0 >0). The variations in zeta potentials indicated that ion exchange occurred during Cd2+ and Pb2+ adsorption. FT-IR, XPS and 3D-EEM analyses indicated that the functional groups of the EPSs involved in adsorption were mainly the CO, C-O and C-O-C groups of the polysaccharides; furthermore, fulvic acid-like substances, humic-like substances and tyrosine-like proteins played important roles in the adsorption of Cd2+ and Pb2+ by the different EPS layers.