| Acidithiobacillus ferrooxidans is typically found in acid mine effluents, and is an acidophilic, chemolithotrophic bacteria used for bioleaching metals from minerals, biodesulfurization of coal, removal of metals from waste sludge, and treatment of acid mine drainage. So screening efficient strain, studying the influence actors on oxidation activity and machenism of improving oxidation activity are of great importantance both in theory and practice.A. ferrooxidans grows autotrophically and obtains energy from the oxidation of ferrous iron (Fe2+) and elemental sulfur (S0) or reduced sulfur compounds, using O2as the electron acceptor under oxidizing conditions. An acidophilic iron-sulfur oxidizing bacterium LY01was isolated from acid mine drainage of coal in Guizhou province, China. Strain LY01was identified as Acidithiobacillus ferrooxidans by morphological and physiological characteristics, and phylogenetic analysis of its16S rRNA gene sequence. Strain LY01was capable of growth by using Fe2+, S0and pyrite(FeS2) as sole energy source, respectively, but could hardly use thiosulfate(Na2S2O3). Significant differences in oxidation efficiency and bacterial growth were observed. When strain LY01was cultured in9K medium with44.2g-L-1FeSO4·7H2O as substrate, the oxidation efficiency of Fe2+was100%in30h and number of strain LY01reached to4.2×107cell·mL"1. When LY01was cultured in9K medium with10g-L-1S0as substrates,6.7%S0oxidation efficiency,2001mg-L"1SO42" concentration and8.9×107cell-mL"1cell number were observed in21d respectively. When LYO1was cultured with30g-L"1pyrite as substrates, the oxidation efficiency of pyrite, SO42-concentration and cell number reached10%,4443mg-L"1and3.4x108cell-mL-1respectively in20d.The effects of different heavy metals (Zn2+、Ni2+、Cu2+) on oxidation activity of strain LY01cultured with FeSO4·7H2O were investigated. Results showed that strain LY01had highly ability to tolerate Zn2+and Ni+, and the maximum tolerated concentrations were20g-L-1、16g-L-1respectively.While Cu2+was more toxic than Zn2+and Ni2+to strain LY01, the maximum tolerated concentrations were less than4g-L-1. Meantime, the effects of different heavy metal ions (Zn2+、Cu2+、Ni2+、Pb2+、Ag+) on oxidation activity of strain LYO1cultured with pyrite were researched. Results showed that the oxidation activity of strain LY01was inhibited at a certain extent with10～100mg-L-1Zn2+, Ni2+, Cu2+, Ag+respectively, and the inhibitory effect of Ag+on oxidation activity of strain LY01increased with the increase of Ag+concentration, but the addition of10～100mg-L-1Pb2+had no effect on LY01activity. The stress of different heavy metal ions on oxidation activity of strain LY01was Cu2+>Zn2+>Ni2+>Ag+>Pb2+.The oxidizing pyrite activity of strain LY01cells grown-FeSO4, S0and pyrite respectively were studied comparativily. Significant differences in oxidation efficiency were observed. The oxidation activity of strain LY01cells grown-pyrite were the most, followed by cells grown-S0, cells grown-FeSO4were the weakest. The mechanisms of different oxidizing activity were studied, such as the morphology of cells, characteristics of extracellular polymeric substances (EPS) from cells, FTIR of cells, secondary minerals, pyrite adsorption rates etc.The morphology characteristic of strain LY01cells grown-FeSO4, S0and pyrite respectively were changed by the transmission electron microscope. Strain LY01cells grown-pyrite secreted abundant EPS attached on the surface of cells, however, less EPS was observed when LY01was cultured with either S0or Fe2+. EPS produced from A. ferrooxidans LY01cells grown-pyrite was39mgC (TOC)·L-1, and EPS bonding Fe3+was3.89mg/mgC (TOC). While EPS from A. ferrooxidans LY01cells grown-FeSO4was11mgC·L-1and EPS bonding Fe3+were1.02mg/mgC. The results also showed that there were significant differences in cells attachment; LY01cells grown-pyrite and S were easier to adsorption on the surface of pyrite than that cells grown-FeSO4.It was presented that the composition of the cells grown-substrate(S0, Fe2+and FeS2, respectirely) were almost same by the FTIR spectra, for example, either of cell containing-OH、NH2、C=O、C-O functional groups, respectively. But strain LY01cells grown-pyrite and S0had more hydrophobic groups, such as R-O and C-X. The precipitates produced from strain LY01cultured with FeSO4and FeS2analysed by the X-ray diffraction, the result showed that both of which were the mixture of jarosite and ammonium jarosite. But the former mainly was ammonium jarosite, and the latter mainly was jarosite. LY01cultured with the hydrophobic substrates such as S0and FeS2, the secondary minered production from oxidation process obviously decreased. What’s more, bacteria cells cultured with the hydrophobic substrates were more easily to adhere to the surface of the pyrite, and accelerated mine leaching. |
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