Different survival strategies of the phosphate-mineralizing bacterium Enterobacter sp. PMB-5 in response to cadmium stress: Biomineralization, biosorption, and bioaccumulation

The phosphate-mineralizing bacteria (PMBs) has shown great potential as a sustainable solution to support pollution remediation through its induced mineralization capacity. However, few studies have been conducted on the mechanism of cadmium (Cd) tolerance in PMBs. In this study, a PMB strain, Enterobacter sp. PMB-5, screened from Cd-contaminated rhizosphere soil, has high resistance to Cd (540 - 1220 mg/L) and solubilized phosphate (232.08 mg/L). The removal experiments showed that the strain PMB-5 removed 71.69-98.24% and 34.83-76.36% of Cd with and without biomineralization, respectively. The characterization result of SEM, EDS, TEM, XPS and XRD revealed that PMB-5 induced Cd to form amorphous phosphate precipitation through biomineralization and adopted different survival strategies, including biomineralization, bioaccumulation, and biosorption to resistance Cd in the microbial induced phosphate precipitation (MIPP) system and the non-MIPP system, respectively. Moreover, the results of whole genome sequencing and qRT-PCR indicated that phosphorus metabolism genes such as pst, pit, phn, ugp, ppk, etc. and heavy metal tolerance genes (including ion transport, ion efflux, redox, antioxidant stress), such as czcD, zntA, mgtA, mgtC, katE, SOD2, dsbA, cysM, etc. were molecular for the PMB-5 mineralization and Cd tolerance of PMB-5. Together, our findings suggested Enterobacter sp. PMB-5 is a potential target for developing more effective bioinoculants for Cd contamination remediation.