Auxin acts as a downstream signaling molecule involved in hydrogen sulfide-induced chilling tolerance in cucumber.

MAIN CONCLUSION: This report proves a cross talk between H2S and IAA in cold stress response, which has presented strong evidence that IAA acts as a downstream signal mediating the H2S-induced stress tolerance in cucumber seedlings. We evaluated changes in endogenous hydrogen sulfide (H2S) and indole-3-acetic acid (IAA) emission systems, and the interactive effect of exogenous H2S and IAA on chilling tolerance in cucumber seedlings. The results showed that chilling stress increased the activity and relative mRNA expression of L-/D-cysteine desulfhydrase (L-/D-CD), which in turn induced the accumulation of endogenous H2S. Similarly, the endogenous IAA system was triggered by chilling stress. We found that 1.0 mM sodium hydrosulfide (NaHS, an H2S donor) significantly enhanced the activity of flavin monooxygenase (FMO) and relative expression of FMO-like proteins (YUCCA2), which in turn elevated endogenous IAA levels in cucumber seedlings. However, IAA had little effects on activities of L-/D-CD and endogenous H2S levels. H2S-induced IAA production accompanied by increase in chilling tolerance, as shown by the decrease in stress-induced electrolyte leakage (EL) and reactive oxygen species (ROS) accumulation, and increase in gene expressions and enzyme activities of photosynthesis. 1-naphthylphthalamic acid (NPA, an IAA polar transport inhibitor) declined H2S-induced chilling tolerance and defense genes' expression. However, scavenging of H2S had a little effect on IAA-induced chilling tolerance. These results suggest that IAA acting as a downstream signaling molecule is involved in the H2S-induced chilling tolerance in cucumber seedlings.

Study on application of biological iron sulfide composites in treating vanadium-extraction wastewater containing chromium (VI) and chromium reclamation.

In this study, the Cr(VI)-resistant properties and regeneration characteristics of biological iron sulfide composites were investigated, which consist of sulfate reducing bacteria (SRB) and its in situ synthesized nanosized iron sulfides. Then the application of the composites in treating vanadium-extraction wastewater containing high concentration Cr(VI) and reclaiming Cr were performed. It was found that SRB in composites still survived after being used to treat vanadium-extraction wastewater, which could reduce reaction products Fe3+ and sulphur into Fe2+ and S2 by using them as the electron accepters and thus regenerating biological iron sulfide composites. The SRB also could be resistant to 600 mgl(-1) Cr(VI) and reduce it gradually. Based on the Cr(VI)-resistant properties and regeneration characteristics of the composites, a reduction-regeneration recirculation process for treating vanadium-extraction wastewater and reclamation of Cr was developed. The results indicated that the contaminants in effluent reached the Chinese discharge standard of pollutants for vanadium industry (GB 26452-2011), i.e. the concentration of total Cr(TCr) was less than 0.912 mgl(-1), Cr(VI) was less than 0.017 mgl(-1) and V was less than 0.260 mgl(-1). After 10 cycles of treatment, the Cr2O3 content in sludge reached 41.03%, and the ratio of Cr2O3/FeO was 7.35. The sludge reached the chemical and metallurgical (hydrometallurgy) grade of chromite ore and could be reclaimed.

[Property analysis of nanosized iron sulfide produced by sulfate reducing bacteria and its application in the treatment of wastewater containing high concentration of Cr (VI)].

The properties of novel nanosized iron sulphide produced by sulfate reducing bacteria (SRB) and its application to the removal of Cr (VI) from wastewater were studied. The structural properties were examined by transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The influences of pH, temperature and dosage on removal of Cr (VI) from wastewater by nanosized iron sulphide were investigated, and the effect comparison of nanosized iron sulphide and other traditional wastewater treatment was also evaluated. TEM result shows that the length of the nanosized iron sulphide is approximately 45-80 nm, and the ratio of length to width is 10-15. XPS and XRD results indicate that the Fe/S is 1.07-1.11, and the main composition of nanosized iron sulphide is amorphous FeS and mackinawite. While in treating wastewater containing Cr (V), pH, temperature and dosage of nanosized iron sulphide are the main factors to control the reaction. The Cr (VI) reduction rate increases with decrease of pH and increase of dosage and temperature. Among these factors, pH is the most significant influence factor. At 25 degrees C, pH 3, when the mole ratio of nanosized iron sulphide to chromium (VI) reaches 1.17/1, wastewater containing Cr (VI) 0.03 mol/L can be treated to meet the discharge standard within 10 min. Moreover, in treating wastewater containing Cr (VI), compared with commercial iron sulfide (AR.), nanosized iron sulphide has advantages of low dosage and short treatment time, and compared to conventional biological treatment by SRB, nanosized iron sulphide has advantages of low effluent COD and small amount of sludge.

Study on application of biological iron sulfide composites in treating vanadium-extraction wastewater containing chromium (VI) and chromium reclamation.

In this study, the Cr(VI)-resistant properties and regeneration characteristics of biological iron sulfide composites were investigated, which consist of sulfate reducing bacteria (SRB) and its in situ synthesized nanosized iron sulfides. Then the application of the composites in treating vanadium-extraction wastewater containing high concentration Cr(VI) and reclaiming Cr were performed. It was found that SRB in composites still survived after being used to treat vanadium-extraction wastewater, which could reduce reaction products Fe3+ and sulphur into Fe2+ and S2- by using them as the electron acceptors and thus regenerating biological iron sulfide composites. The SRB also could be resistant to 600 mgl-1 Cr(VI) and reduce it gradually. Based on the Cr(VI)-resistant properties and regeneration characteristics of the composites, a reduction-regeneration recirculation process for treating vanadium-extraction wastewater and reclamation of Cr was developed. The results indicated that the contaminants in effluent reached the Chinese discharge standard of pollutants for vanadium industry (GB 26452-2011), i.e. the concentration of total Cr(TCr) was less than 0.912 mgl-1, Cr(VI) was less than 0.017 mgl-1 and V was less than 0.260 mgl-1. After 10 cycles of treatment, the Cr2O3 content in sludge reached 41.03%, and the ratio of Cr2O3/FeO was 7.35. The sludge reached the chemical and metallurgical (hydrometallurgy) grade of chromite ore and could be reclaimed.