One bioleaching bacterium, named as strain DXS, was isolated from acid mine drainages (AMDs) of Dongxiangshan Mine of Hami, Xinjiang Province, China. The strain DXS is gram-negative and rod-shaped with a size of (0.40±0.05) μm×(1.3±0.5) μm. The optimal temperature and pH for growth are 30 ℃ and pH 2.0, respectively. It can grow autotrophically by using ferrous iron, elemental sulfur and NaS2O3 as sole energy sources. In the phylogenetic tree, strain DXS has similarity with Acidithiobacillus ferrooxidans type strain ATCC 23270 with 99.57% sequence similarity. The cloning and sequencing of Iro protein gene (iro) and tetrathionate hydrolase gene (tth) reveal that strain DXS is completely identical in iro gene sequence to A. ferrooxidans LY (DQ166841), and almost identical in tth gene sequene to A. ferrooxidans (AB259312) (only two nucleotides change). The bioleaching experiments of marmatite and pyrite reveal that the leached zinc and iron concentrations reach 3.01 g/L and 2.75 g/L, respectively. The strain has a well potential application in industry bioleaching.
This work presents a study for chemical leaching of sphalerite concentrate under various constant Fe3+ concentrations and redox potential conditions. The effects of Fe3+ concentration and redox potential on chemical leaching of sphalerite were investigated. The shrinking core model was applied to analyze the experimental results. It was found that both the Fe3+ concentration and the redox potential controlled the chemical leaching rate of sphalerite. A new kinetic model was developed, in which the chemical leaching rate of sphalerite was proportional to Fe3+ concentration and Fe3+ /Fe2+ ratio. All the model parameters were evaluated from the experimental data. The model predictions fit well with the experimental observed values.
Reverse-transcription qualitative PCR(RT-qPCR)was used to analyze the changes in transcription levels of the sulfur metabolism-related periplasmic protein genes of Acidithiobacillus ferrooxidans ATCC 23270 grown on sulfur or ferrous.Seven periplasmic proteins with apparently higher abundance grown on elemental sulfur than on ferrous sulfate were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF-MS).Expression analysis of the corresponding genes by RT-qPCR shows that the constitutive expression of all those genes are more up-regulated grown on sulfur than those grown on ferrous(>10 folder).Study on the corresponding genes of the identified periplasmic proteins by RT-qPCR confirmed the results of two-dimensioned gel electrophoresis,indicating they may be related with sulfur metabolism in A.ferrooxidans.
A total of 126 bacterial strains were isolated from soil samples.Among them,11 isolates were found positive for amylase production.Strain YL produced the largest zone of clearance on plate assay.The isolate YL was identified as Bacillus sp.based on morphological and physiochemical characterization.According to 16S rRNA gene sequencing data,the closest phylogenetic neighbor of strain YL was Bacillus amyloliquefaciens(99.54%).After that,an optimization of culture conditions was carried out for the improvement of α-amylase production.Response surface methodology(RSM) was applied to evaluate the effect of medium components including wheat bran,cottonseed extract,yeast extract,starch,NaCl and CaCl2.Three variables(wheat bran,cottonseed extract,and starch),which were identified to significantly affect amylase production by Plackett-Burman design were further optimized using response surface methodology of Box-Behnken design(BBD).The optimal concentrations estimated for each variable related to the maximum of amylase activity(86 kU/mL) were 10.80 g/L wheat bran,9.90 g/L cottonseed extract,0.5 g/L starch,2.0 g/L yeast extract,5.00 g/L NaCl and 2.00 g/L CaCl2.The fermentation using optimized culture medium allowed a significant increase in amylase production(by 3-fold).The improvement in the α-amylase production after optimization process can be considered adequate for large-scale applications.
The original strains Acidithiobacillus ferrooxidans GF and Acidiphilium cryptum DX1-1 were isolated from the drainage of some caves riched in chalcopyrite in Dexing Mine in Jiangxi Province of China.The optimum temperature and pH for growth were 30℃and 3.5 for Ac.cryptum DX1-1,and 30℃and 2.0 for At.ferrooxidans GF,respectively.For Ac.cryptum DX1-1,the optimum UV radiating time was 60 s and the positive mutation rate was 22.5%.The growth curves show that Ac.cryptum after mutagenesis reached stationary phase within 60 h,which was 20 h earlier than the original strain.For At.ferrooxidans GF,the optimum mutation time was 60 s and the positive mutation rate was 35%.The most active UV-mutated strain At.ferrooxidans GF oxidized all the ferrous after 48 h.The bioleaching experiments showed that bioleaching with the mixture of UV-mutated strains of At.ferrooxidans GF and Ac.cryptum DX1-1(1:1)could extract 3.01 g/L of copper after 30 d,while the extracted copper was 2.63 g/L with the mixture of the original strains before UV-mutation.At the end of the bioleaching experiments,the proportion of the cell density in the cultures of Ac.cryptum DX1-1 and At.ferrooxidans GF was approximately 1:5.
