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Pb is a toxic heavy metal in contaminated soil and water, resulted from industrial activities, mine exploration, etc. Phosphate solubilizing bacteria are able to secrete organic acids and further to enhance the solubility of phosphates. Enterobacter. sp and geological fluorapatite (FAp) were applied to investigate the biotransformation of Pb 2+ in solution with SO 4 2− , PO 4 3− , and Cl − species by ICP-OES, ATR-IR, XRD, and SEM. Enterobacter. sp can lower pH of the medium to ∼4. Meanwhile, >90% mobile Pb (declining from 1000 to 30 ppm) was immobilized via the combination of Enterobacter. sp and FAp. With the addition of FAp and Pb, pyromorphite was precipitated, but with relatively low content. In contrast, abundant anglesite mineral was formed in such weakly acidic system. These anglesite crystals can even absorb phosphates particles onto their surface. Additionally, geochemical modeling confirms the formation of anglesite and cerussite under weekly acidic and alkalic condition respectively, especially when H 2 PO 4 − concentration <10 −8 mM. Furthermore, the presence of Cl − in solution leads to the formation of chloropyromorphite when H 2 PO 4 − concentration >10 −12 mM, especially under neutral environment. This study explored the biotransformation of Pb in SO 4 -PO 4 -Cl aqueous system and hence provided guidance on bioremediation of Pb by bacteria and FAp. [ABSTRACT FROM AUTHOR]

Clay minerals can adsorb both microorganisms and heavy metals. In this study, typical soil bacterium, Enterobacter sp. was applied to investigate the potential protection of the bacterial cells from Pb2+ stress by clay minerals. The sorption by two representative types of montmorillonite (Mt) were contrasted, i.e., Mt s /Mt w with strong/weak CEC. There was no significant difference between the two clay minerals regarding their adsorption of Pb2+ cations in water (i.e., ~55 mg L-1). However, the sorption of bacterial cells on the two clay minerals showed evident contrasts , which resulted in the different capacity of Pb sorption. Mt s with high CEC preferentially adsorbed abundant bacterial cells (rather than Pb2+) on its surface. The residual Pb2+ concentration in solution actually raised by 7.5% after the addition of Enterobacter sp. In addition, both the Pb-contaminated cells and "healthy" cells (with low Pb contamination) could be adsorbed onto Mt surface, whereas the latter dominated the adsorbents on Mt s. This was due to that the Mt s with high CEC could provide more exchangeable cations, building more cation bridging ligands between the microbial cells (whatever the types of cells) and clay surface. Furthermore, the adsorbed "healthy" bacterial cells might escape from clay surface via "self-liberating" mechanism, i.e., increasing electrostatic repulsion between the bacteria and clay during microbial decomposition of the medium. This study hence elucidated the protection of microorganisms from Pb2+ stress by Mt. ga1 • There was no significant difference of Pb2+ sorption between the two Mt with different sorption capacity. • Mt with higher CEC can adsorbed more bacterial cells on its surface. • Pb2+ created bridging ligands between the microbial cells and clay surface. • The adsorbed cells might escape from clay surface via increasing electrostatic repulsion between the bacteria and clay. [ABSTRACT FROM AUTHOR]

Application of biochar in heavy metal remediation suffers from lack of long-term stability. Phosphate-solubilizing bacteria (PSB) are able to elevate P release and the subsequent reaction with Pb to form stable pyromorphite. This study investigated the feasibility of applying PSB modified biochar to enhance immobilization of Pb2+. An alkaline biochar produced from rice husk (RB) and a slightly acidic biochar produced from sludge (SB) were selected. It showed that the biochars can effectively remove Pb2+ via adsorption, i.e., aqueous Pb concentrations after RB and SB addition were reduced by 18.61 and 53.89% respectively. The addition of PSB increased the Pb2+ removal for both biochars (to 24.11 and 60.85%, respectively). In particular, PSB significantly enhanced the formation of stable pyromorphite on surface of SB. This is due to that the evenly distributed PSB enhanced P release and regulated pH on the biochar surface. Moreover, small particles (<0.074 mm) showed their higher ability to induce the formation of pyromorphite, for both RB and SB. Nevertheless, SB demonstrated higher capability of sorption, together with its more abundant P content, which provided a more suitable platform to attract PSB to immobilize heavy metals. Therefore, the combination of biochar and PSB is a promising candidate material for heavy metal remediation. However, the types and particle size distribution of biochar should be addressed. Unlabelled Image • The combination of biochar and phosphate-solubilizing bacteria (PSB) successfully removed Pb2+ from organic medium. • XRD, ATR-IR and SEM/EDS show the formation of pyromorphite on biochar by PSB. • The decomposition of phosphorus compounds by bacteria and the increase of pH value were helpful in the solubilization of P and the subsequent formation of pyromorphite • P release from medium and biochar significantly promotes formation of pyromorphite. • PSB contribute to the decreased formation of cerussite on biochar surface. [ABSTRACT FROM AUTHOR]

Bioapatite (BAp) is regarded as an effective material to immobilize lead (Pb 2+ ) via the formation of stable pyromorphite. However, when applied in contaminated soil, due to its low surface area and low adsorption capacity, BAp might not sufficiently contact and react with Pb 2+ . Biochar, a carbon storage material, typically has high surface area and high adsorption capacity. This study investigated the feasibility of using biochar as a reaction platform to enhance BAp immobilization of Pb 2+ . An alkaline biochar produced from wheat straw pellets (WSP) and a slightly acidic biochar produced from hardwood (SB) were selected. The results of aqueous adsorption showed the combination of biochar (WSP or SB) and BAp effectively removed Pb 2+ from the aqueous solution containing 1000 ppm Pb 2+ . XRD, ATR-IR, and SEM/EDX results revealed the formation of hydroxypyromorphite on both biochars’ surfaces. This study demonstrates that biochars could act as an efficient reaction platform for BAp and Pb 2+ in aqueous solution due to their high surface area, porous structure, and high adsorption capacity. Therefore, it is mechanistically feasible to apply biochar to enhance BAp immobilization of Pb 2+ in contaminated soil. [ABSTRACT FROM AUTHOR]

The coexistence of heavy metals in aquatic systems causes complex toxicity in microorganisms. In this study, we explored the influences of Pb2+ addition on Cd2+ toxicity in Rhodotorula mucilaginosa (Rho). Cd toxicity alone was tested with up to 200 mg/L Cd2+ to induce stress. Cell counts and Cd2+ removal rates declined to a minimum when the Cd2+ concentration reached 150 mg/L, confirming strong Cd-induced toxicity. Then, co-existence of Pb2+ and Cd2+ was established as Pb-CdH (Pb/Cd = 1, molar ratio), Pb-CdM (Pb/Cd = 10), and Pb-CdL (Pb/Cd = 100). The Pb-CdL and Pb-CdM treatments showed clear similarities in terms of their effects on cell counts, polysaccharide concentrations, and cell morphology. There was also no significant difference in their gene expression profiles. The competition between the two types of cations caused preferential extra/intracellular sorption of less toxic Pb2+. Moreover, the expression of genes related to glycolysis, the TCA cycle, and oxidative phosphorylation was significantly enhanced in the cells with Pb-CdH treatment, suggesting that these cells were functional. Furthermore, the excitability-caused increase in the cell count after Pb-CdH treatment (Cd2+ = 112.4 mg/L) was 30% higher than that of the 100 mg/L Cd2+ treatment. These results proved that the addition of Pb2+ in solution significantly weakened the toxicity of Cd2+. [Display omitted] • Rho cells have the preferential sorption of Pb2+ under coexistence of Cd2+. • Cd toxicity is weakened as the less-toxic Pb2+ occupy the active binding sites. • The strategy of cell reproduction strengthens fungal ability to resist HM stress. • Sorption of HM by daughter cells were significantly lower than the mother cells. [ABSTRACT FROM AUTHOR]