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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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

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]

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]