Bioreduction mechanisms of high-concentration hexavalent chromium using sulfur salts by photosynthetic bacteria.

Eliminating "sulfur starvation" caused by competition for sulfate transporters between chromate and sulfate is crucial to enhance the content of sulfur-containing compounds and improve the tolerance and reduction capability of Cr(VI) in bacteria. In this study, the effects of sulfur salts on the Cr(VI) bioremediation and the possible mechanism were investigated in Rhodobacter sphaeroides SC01 by cell imaging, spectroscopy, and biochemical measurements. The results showed that, when the concentration of metabisulfite was 2.0 g L-1, and the initial OD600 was 0.33, the reduction rate of R. sphaeroides SC01 reached up to 91.3% for 500 mg L-1 Cr(VI) exposure at 96 h. Moreover, thiosulfate and sulfite also markedly increased the concentration of reduced Cr(VI) in R. sphaeroides SC01. Furthermore, the characterization results revealed that -OH, -CONH, -COOH, -SO3, -PO3, and -S-S- played a major role in the adsorption of Cr, and Cr(III) reduced by bacteria was bioprecipitated in the production of Cr2P3S9 and CrPS4. In addition, R. sphaeroids SC01 combined with metabisulfite significantly increased the activity of glutathione peroxidase and the content of glutathione (GSH) and total sulfhydryl while decreasing reactive oxygen species (ROS) accumulation and cell death induced by Cr(VI) toxic. Overall, the results of this research revealed a highly efficient and reliable strategy for Cr(VI) removal by photosynthetic bacteria combined with sulfur salts in high-concentration Cr(VI)-contaminated wastewater.

Highly efficient and sustainable removal of Cr (VI) in aqueous solutions by photosynthetic bacteria supplemented with phosphor salts.

Photosynthetic bacteria have flexible metabolisms and strong environmental adaptability, and require cheap, but plentiful, energy supplements, which all enable their use in Cr(VI)-remediation. In this study, the effects of culture conditions on the total Cr removal rate were investigated for a newly identified strain of Rhodobacter sphaeroides SC01. The subcellular distribution and Cr(VI) reduction ability of four different cellular fractions were evaluated by scanning electron microscopy and transmission electron microscopy. Experiments indicated that the optimal culture conditions for total Cr removal included a culture temperature of 35 °C, pH of 7.20, an NaCl concentration of 5 g L-1, a light intensity of 4000 lx, and an initial cell concentration (OD680) of 0.15. In addition, most Cr was found in the cell membrane in the form of Cr (III) after reduction, while cell membranes had the highest Cr(VI) reduction rate (99%) compared to other cellular components. In addition, the physical and chemical properties of SC01 cells were characterized by FTIR, XPS, and XRD analyses, confirming that Cr was successfully absorbed on bacterial cell surfaces. CrPO4‧6H2O and Cr5(P3O10)3 precipitates were particularly identified by XRD analysis. After screening supplementation with five phosphor salts, Cr(VI) reduction due to bioprecipitation was improved by the addition of Na4P2O7 and (NaPO3)6 salts, with the Cr(VI)-reduction rate combined with Na4P2O7 addition being 15% higher than that of the control. Thus, this study proposes a new Cr(VI)-removal strategy based on the combined use of photosynthetic bacteria and phosphor salts, which importantly increases its potential application in treating wastewater.

Effects of arsenic disulfide on apoptosis, histone acetylation, toll like receptor 2 activation, and erythropoiesis in bone marrow mononuclear cells of myelodysplastic syndromes patients in vitro.

OBJECTIVE: As the main component of traditional Chinese medicine realgar, arsenic disulfide (As2S2) is widely used in treating myelodysplastic syndromes (MDS). The goal of the current study is to assess the effects of As2S2 on bone marrow mononuclear cells (BMMNC) of MDS. METHODS: BMMNCs were obtained from 10 lower risk MDS patients, 5 higher risk MDS patients, and 3 healthy controls. Then, the cells were treated with As2S2 for 48h, using vorinostat (also known as SAHA) as control. Cell proliferation and apoptosis were detected. mRNA and protein levels of histone deacetylase-1 (HDAC1), Toll-like receptor 2 (TLR2), and erythroid transcription factor (GATA-1) were detected by quantitative real-time PCR and western blot analysis. RESULTS: After As2S2 treatment in concentrations ranging from 3.125 to 100µmol/L, cell proliferation was inhibited in both lower risk and higher risk MDS. Fifty percent inhibitory concentrations were 24.4µmol/L and 23.6µmol/L, respectively, for lower and higher risk MDS. Apoptotic cells significantly increased in both types of MDS. mRNA and protein levels of HDAC1 and TLR2 were reduced, whereas GATA-1 was increased in both types of MDS. CONCLUSIONS: As2S2 could inhibit cell proliferation and induce apoptosis through histone acetylation modulation in MDS. Similar to SAHA, As2S2 could reduce TLR2 activation and increase GATA-1 expression. Current data suggest epigenetic and immunological alternations are involved in therapeutic mechanisms of realgar in the treatment of MDS.