Lexian Xia

Chemical composition and antioxidant activities of Russula griseocarnosa sp. nov.

Pileus and stipe of mushroom Russula griseocarnosa from South China were analyzed separately for chemical composition and antioxidant activities. The wild mushroom species proved to have antioxidant potential, using assays of reducing power, chelating effect on ferrous ions, scavenging effect on hydroxyl free radicals, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. The mushroom contained very useful phytochemicals such as phenolics, flavonoids, ergosterol, and beta-carotene. The phenolic composition of R. griseocarnosa was analyzed by high-performance liquid chromatography (HPLC). The major component in R. griseocarnosa was quercetin (95.82 microg/g). The combination of bioactive substances and rich nutritional composition (high contents in protein and carbohydrates, low content in fat) in the mushroom should be useful to consumers in encouraging them to utilize the nutritive potential of this edible wild mushroom.

Single and cooperative bioleaching of sphalerite by two kinds of bacteria——Acidithiobacillus ferriooxidans and Acidithiobacillus thiooxidans

Abstract A cooperative bioleaching ( Acidithiobacillus ferriooxidans and Acidithiobacillus thiooxidans ) and single bioleaching ( Acidithiobacillus ferriooxidans or Acidithiobacillus thiooxidans ) of sphalerite were investigated by X-ray diffractometry, energy dispersive spectrography and scanning electron microscopy. The experimental results show that the leaching rate of zinc in the mixed culture is higher than that in pure culture and the sterile control. In these processes, two kinds of bacteria perform different functions and play a cooperative role during leaching of sphalerite. The bioleaching action carried out by Acidithiobacillus ferriooxidans ( A. ferriooxidans ) is not directly performed through Fe 2+ but Fe 3+ , and its role is to oxidize Fe 2+ to Fe 3+ and maintain a high redox potential. Moreover, the addition of an appropriate concentration of ferric iron to the leaching systems is beneficial to zinc dissolution. In the leaching systems without Acidithiobacillus thiooxidans ( A. thiooxidans ), elemental sulfur layers are formed on mineral surface during the dissolution of zinc and block continuous leaching. Acidithiobacillus thiooxidans , however, eliminate the passivation and cause the bioleaching process to continue in the leaching systems. At the same time, protons from the bacterial oxidization of the elemental sulfur layers also accelerate the leaching of zinc.

Relationships among bioleaching performance, additional elemental sulfur, microbial population dynamics and its energy metabolism in bioleaching of chalcopyrite

Abstract To estimate the relationships among bioleaching performance, additional elemental sulfur (S0), microbial population dynamics and its energy metabolism, bioleaching of chalcopyrite by three typical sulfur- and/or iron-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum and Acidithiobacillus thiooxidans with different levels of sulfur were studied in batch shake flask cultures incubated at 30°C. Copper dissolution capability (71%) was increased with the addition of 3.193 g/L S0, compared to that (67%) without S0. However, lower copper extraction was obtained in bioleaching with excessive sulfur. Microbial population dynamics during chalcopyrite bioleaching process was monitored by using PCR-restriction fragment length polymorphism (PCR-RFLP). Additional S0 accelerated the growth of sulfur-oxidizing bacteria, inhibited the iron-oxidizing metabolism and led to the decrease of iron-oxidizing microorganisms, finally affected iron concentration, redox potential and bioleaching performance. It is suggested that mixed iron and sulfur-oxidizing microorganisms with further optimized additional S0 concentration could improve copper recovery from chalcopyrite.

Comparison of bioleaching behaviors of different compositional sphalerite using Leptospirillum ferriphilum, Acidithiobacillus ferrooxidans and Acidithiobacillus caldus

Two sphalerite samples with different iron/sulphur (Fe/S) ratios, Shuikousan ore (Fe/S 0.2) and Dachang ore (Fe/S 0.52), were processed using three microbial species, Leptospirillum ferriphilum, Acidithiobacillus ferrooxidans and Acidithiobacillus caldus. Following 20 days of bioleaching in shake flask cultures, a higher zinc (Zn) extraction (96%) was achieved with Shuikousan ore than with Dachange ore (72%). The extraction efficiency increased when elemental S was added to Dachang ore to attain the same Fe/S ratio as that for Shuikousan ore. Following the addition of S, the redox potential, pH and total dissolved Fe for Dachang ore demonstrated similar behaviors to those of Shuikousan ore. Acidithiobacillus caldus and L. ferriphilum became the dominant species during the bioleaching of sphalerite with a high Fe/S ratio. In contrast, the dominant species were A. ferrooxidans and A. caldus during the bioleaching of sphalerite with a low Fe/S ratio. These results show that the Fe/S ratio has a significant influence on the bioleaching behavior of sphalerite and the composition of the microbial community.

Attachment of Acidithiobacillus ferrooxidans onto different solid substrates and fitting through Langmuir and Freundlich equations.

Attachments of Acidithiobacillus ferrooxidans ATCC 23270 onto elemental sulfur, quartz and complex chalcopyrite were investigated by analysis of its extracellular polymeric substances as well as applying Langmuir and Freundlich equations. The two equations fitted the adsorption equilibrium data with significant correlation coefficient over 0.9. This indicated that bacterial attachment is complicated and involves Langmuir and Freundlich characterizations. Sulfur-grown cells showed the highest affinity for the three solid substrates. The investigated complex chalcopyrite possessed a higher maximum adsorption capacity for A. ferrooxidans than elemental sulfur or quartz. The Freundlich fitting parameters suggested that quartz had a weaker adsorption capacity and smaller adsorption areas than elemental sulfur or the complex chalcopyrite. It is not the content of total carbohydrates or proteins in EPS but their ratios that determine the affinity differences between cells and substrates.

Metabolic changes of Acidithiobacillus caldus under Cu2+ stress

Metabolic changes were investigated by measuring the depletion of dissolved oxygen and the enzymatic activities of sulfur metabolism in Acidithiobacillus caldus (A. caldus) before and after copper stress. The results showed that high concentrations of Cu2+ have an indirect negative effect on the sulfite oxidase and the APS reductase involved in sulfur metabolism when A. caldus is cultured in medium with elemental sulfur as its growth energy. This leads to a decrease in the respiration rate and the growth rate. The changes of activity are negatively correlated with the intracellular Cu2+ concentration through an indirect interaction mechanism. A. caldus was able to induce an efflux of copper ions by forming an ATPase‐dependent pump, which transported copper ions by consuming ATP. The negative effect of Cu2+ on the bacterial metabolism could be minimized by the copper efflux when the bacteria were adapted in medium containing Cu2+ for a long time. However, this bacterial rejuvenation became weaker when grown in medium containing higher concentrations of copper ions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Expression, purification and characterization of an iron-sulfur cluster assembly protein, IscU, from Acidithiobacillus ferrooxidans.

An iron-sulfur cluster assembly protein, IscU, is encoded by the operon iscSUA in Acidithiobacillus ferrooxidans. The gene of IscU was cloned and expressed in Escherichia coli. The protein was purified by one-step affinity chromatography to homogeneity. The protein was in apo-form, the [Fe2S2] cluster could be assembled in apoIscU with Fe2+ and sulfide in vitro, and in the presence of IscA and IscS, the IscU could utilize l-cysteine and Fe2+ to synthesize [Fe2S2] cluster in the protein. Site-directed mutagenesis for the protein revealed that Cys37, Asp39, Cys63 and Cys106 were involved in ligating with the [Fe2S2] cluster.