Efficient remedies for living organisms including bacteria to counteract cadmium (Cd 2+ ) toxicity are still highly needed. Plant toxicity studies have showed that exogenous S(-II) (including hydrogen sulfide and its ionic forms, i.e., H 2 S, HS − , and S 2− ) application can effectively alleviate adverse effects of Cd stress, but whether S(-II) could mitigate bacterial Cd toxicity remains unclear. In this study, S(-II) was applied exogenously to Cd-stressed Shewanella oneidensis MR-1 and the results showed that S(-II) can significantly reactivate impaired physiological processes including growth arrest and enzymatic ferric (Fe(III) reduction inhibition. The efficacy of S(-II) treatment is negatively correlated with the concentration and time length of Cd exposure. Energy-dispersive X-ray (EDX) analysis suggested the presence of cadmium sulfide inside cells treated with S(-II). Both compared proteomic analysis and RT-qPCR showed that enzymes associated with sulfate transport, sulfur assimilation, methionine , and glutathione biosynthesis were up-regulated in both mRNA and protein levels after the treatment, indicating S(-II) may induce the biosynthesis of functional low-molecular-weight (LMW) thiols to counteract Cd toxicity. Meanwhile, the antioxidant enzymes were positively modulated by S(-II) and thus the activity of intracellular reactive oxygen species was attenuated. The study demonstrated that exogenous S(-II) can effectively alleviate Cd stress for S. oneidensis likely through inducing intracellular trapping mechanisms and modulating cellular redox status. It suggested that S(-II) may be a highly effective remedy for bacteria such as S. oneidensis under Cd-polluted environments.
Kunjie Hou,Zhoujie Pi,Fei Chen,Li He,Fubing Yao,Shengjie Chen,Xiaoming Li,Haoran Dong,Qi Yang
The practical application of the traditional Fenton system (Fe(II)/H2O2) is seriously hampered by the sluggish Fe(III)/Fe(II) cycle and the stringent acidic reaction condition. In this work, we found that trace-dissolved S(-II) (DS(-II), 5 μM) could significantly accelerate the Fe(III)/Fe(II) cycle and trigger a rapid H2O2 activation process in the Fe(III)/H2O2 system. Thus, more hydroxyl radicals (·OH) were generated for the rapid removal of various organic pollutants such as bisphenol A (BPA) and sulfamethoxazole (SMX) from water. Besides, the additive DS(-II) effectively broadened the application pH range of the Fenton or Fenton-like system. The constructed Fe(III)/DS(-II)/H2O2 system showed extensive applicability to different water matrices and maintained high BPA removal in the actual water sources. Furthermore, the toxicity assessment revealed that the toxicity of the target contaminant was diminished. The harmless SO42– was the final product of DS(-II) in the Fe(III)/DS(-II)/H2O2 system, and the residual DS(-II) was less than the threshold limit value for fresh or saltwater (0.5 mg/L). This discovery is expected to promote the large-scale practical application of iron-based Fenton or Fenton-like systems in practical organic wastewater purification.
Kai Jia,Qiming Feng,Guofan Zhang,Wanying Ji,Wukai Zhang,Bingqian Yang
Smithsonite is a readily dissolvable carbonate mineral that is naturally hydrophilic, making recovery of this ore by flotation difficult. The flotation results showed that conditioning with only sodium sulfide (Na 2 S) did not successfully allow the smithsonite samples to float, whereas treatment with a combination of S(II), Pb(II) and xanthate (with Na 2 S as the sulfurizing reagent, lead ions (Pb(II)) as the activator, and xanthate as the collector) improved the flotation of smithsonite, achieving a mass recovery of 95.8%. A combination of analytical techniques, including X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), in conjunction with depth profiling , was used to investigate the chemical nature of the sulfur and lead species on the smithsonite surface. For S(II)-conditioned smithsonite, a layer of ZnS formed on the smithsonite (ZnCO 3 ) substrates; this newly formed ZnS coating was amorphous or poorly crystallized. For smithsonite samples conditioned with S(II) and Pb(II), the microstructures and the phase constituents, obtained by AFM and XRD analyses, confirmed the formation of the PbS species with a cubic galena structure on the surface. XPS depth profiling showed that the PbS layer was 18-nm thick, which corresponds to 30 PbS molecular layers . This study presents direct evidence that the coating of the activation product, PbS, on the smithsonite surface was similar to a relatively thick galena layer, which led to successful flotation.
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