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Abstract: Microbe–mineral interactions play an important role in affecting geochemical transformations of heavy metals in the soil environment. The formation of metal sulfide, which is mediated by sulfate-reducing bacteria (SRB) through contributing to sulfate reduction is an important pathway for heavy metal stabilization in anoxic soil. In oxic rice rhizospheres, there are abundant sulfur oxidizing bacteria (SOB) which can enhance sulfur oxidation and hence the availability of heavy metals, resulting in the uptake of such metals by the plant and a potential risk to human health. In this study, the potential existence of SRB in oxic rice rhizospheres, their contribution to sulfate reduction, and potential to reduce the availability of heavy metal was investigated. PCR-DGGE fingerprinting and real-time PCR results showed increasing numbers of SRB with Pb addition, which corresponded with increases in soil pH and reduction in Eh, suggesting the enhancement of sulfur reduction and SRB activity. Sulfur K-edge XANES, which characterized sulfur speciation in situ, revealed reduced states of sulfur. The SRB mediated the sulfate reduction and contributed to the formation of reduced sulfur which interacted with Pb, leading to the formation of stable metal sulfide and reduction of Pb availability. In return, acclimated SRB populations developed in Pb-polluted conditions. Hence stabilization of reduced sulfur by Pb enhanced the activity of SRB and sulfate reduction in rice rhizosphere. [Copyright &y& Elsevier]

Fungi Penicillium oxalicum SL2 was applied for Pb 2+ bioremediation in aqueous solution in this study. After 7 days of incubation at different initial concentrations of Pb 2+ (0, 100, 500 and 2500 mg L −1 ), most of Pb 2+ were removed (90, 98.3, and 86.2%), the maximum Pb content in mycelium reached about 155.6 mg g −1  dw. Meanwhile, the formation of extracellular secondary minerals and intracellular Pb-complex were observed and identified, the speciation of Pb in mycelium was also detected by X-ray absorption near-edge structure (XANES) spectroscopy, i.e., Pb-oxalate, Pb-citrate, Pb-hydrogen phosphate and Pb-glutathione analogues. In addition, content of glutathione and oxidized glutathione was increased under the exposure of Pb 2+ , which implied that glutathione might play a key role in Pb immobilization and detoxification in P. oxalicum SL2. This study elucidated partial mechanisms of Pb immobilization and speciation transformation of this strain, providing an alternative biomaterial in the bioremediation of Pb-contaminated wastewater. [ABSTRACT FROM AUTHOR]

As a potential bioremediation strain for Pb contamination, Penicillium oxalicum SL2 sometimes has secondary activation of Pb, so it is crucial to clarify its effect on Pb morphology and its intracellular response to Pb stress. We investigated the effect of P. oxalicum SL2 in medium on Pb2+ and Pb availability in eight minerals, and revealed the prioritization of Pb products. (i)Pb was stabilized within 30 days as Pb 3 (PO 4) 2 or Pb 5 (PO 4) 3 Cl with sufficient phosphorus (P); (ii) under P deficiency but sulfur (S) sufficient, Pb was stabilized mainly in the form of PbSO 4 ; (iii) under conditions of P and S deficiency, Pb was stabilized mainly in the form of PbC 2 O 2. With the help of proteomic and metabolomics analysis, a total of 578 different proteins and 194 different metabolites were found to be matched in 52 pathways. Among them, the activation of chitin synthesis, oxalate production, sulfur metabolism and transporters improved the Pb tolerance of P. oxalicum SL2, and promoted the synergistic effect of extracellular adsorption, bio-precipitation and transmembrane transport on Pb stabilization. Our results fill the gap in the intracellular response of P. oxalicum SL2 to Pb and provide new insights into the development of bioremediation agent and technology for Pb contamination. [Display omitted] • Pb was stabilized within 30 days by P. oxalicum SL2. • The activation of chitin synthesis pathway enhanced extracellular Pb adsorption. • Pb was stabilized as Pb 3 (PO 4) 2 or Pb 5 (PO 4) 3 Cl with sufficient P. • Pb was mainly precipitated in the forms of PbC 2 O 2 and PbSO 4 under P deficiency. • Changes in transporters such as ABC and MFS regulated Pb subcellular distribution. [ABSTRACT FROM AUTHOR]

Abstract: A pot experiment was carried out to study the sulfur (S) and lead (Pb) interaction and its impact on soil microbial community composition in rice rhizosphere soil under flooded conditions. Paddy soil was treated with a Pb gradient with and without thiosulfate addition and then planted with rice. The increasing addition of Pb resulted in plant yield reduction and high, phytotoxic concentrations of Pb in roots with relatively low concentration of Pb in shoots. Under the impact of thiosulfate, Pb uptake in plants and NH4OAc extractable Pb did not increase dramatically. PCR-DGGE experiment suggested that S action led to new bands. Specific clones (T3 and T6) found in S addition soils had high similarity to Thiobacillus, which indicated relatively high rates of potential S oxidation. S addition did not affect the availability Pb and the composition of soil microbial community. S addition is not a suitable amendatory tool of phytoremediation for Pb polluted soil. [Copyright &y& Elsevier]