Trans. Nonferrous Met. Soc. China 25(2015) 3096-3102

Differential utilization and speciation transformation of orthorhombic α-S₈ and amorphous μ-S by substrate-acclimated mesophilic Acidithiobacillus ferrooxidans

Hong-chang LIU^1,2, Jin-lan XIA^1,2, Zhen-yuan NIE^1,2, Lei ZHENG³, Chen-yan MA³, Yi-dong ZHAO³

1. School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China;

2. Key Laboratory of Biometallurgy of Ministry of Education, Central South University, Changsha 410083, China;

3. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

Received 31 October 2014; accepted 9 January 2015

Abstract: The utilization and speciation transformation of α-S₈ and μ-S by the typical mesophilic acidophilic strain Acidithiobacillus ferrooxidans ATCC 23270 were investigated. A. ferrooxidans cells first acclimated to the energy source α-S₈ or μ-S, respectively. The results of cell growth and sulfur oxidation behavior showed that the strain grown on α-S₈ entered slowly (about 1 d later) into the exponential phase, while grew faster in the exponential phase and attained higher maximal cell density and lower pH value than that on μ-S. After bio-corrosion, both of the two sulfur samples were evidently eroded and modified by A. ferrooxidans cells. After growth of A. ferrooxidans, the surface composition of amorphous μ-S became 63.1% μ-S and 36.9% α-S₈, and that of orthorhombic α-S₈ became 68.3% α-S₈ and 31.7% μ-S, while the surface compositions of α-S₈ and μ-S in sterile experiment were not changed, indicating that these two elemental sulfur species can be interconverted by A. ferrooxidans.

Key words: sulfur utilization; sulfur speciation transformation; α-S₈; μ-S; Acidithiobacillus ferrooxidans

1 Introduction

Elemental sulfur (S⁰) oxidation by sulfur-oxidizing microbes (SOMs) takes an important role in bio- hydrometallurgy of metals from sulfide minerals [1]. In bioleaching process, S⁰ may accumulate on the mineral surface as a passivation layer, while the existence of SOMs can eliminate the S⁰ layer by oxidizing S⁰ into sulfuric acid [2].

S⁰ can exist in a wide variety of allotropic forms. Among them, orthorhombic cyclo-octasulfur α-S₈ and amorphous polymeric sulfur μ-S are the two major species. The observed S⁰ produced during bioleaching of metal sulfide minerals has been reported mostly as orthorhombic form [1,3] and in few cases as short chain polysulfides (S_n^2-) and long sulfur chains terminated with organic groups [4,5]. The α-S₈ form was probably chemically transformed by the unstable S_n^2- [6] which was considered as a polymerization process from monosulfide (S^2-) of bulk chalcopyrite via surface S_n^2- to α-S₈. On the other hand, the bio-oxidation of the produced α-S₈ was suggested to be activated firstly by reacting with reactive thiol groups (—SH) of outer membrane proteins, forming —S_nH (n≥2) complexes, and then transported into periplasmic space for further oxidation. This indicated that there might exist transformation between these two S⁰ allotropes. Therefore, it is very valuable to study the differential utilization and sulfur speciation transformation of orthorhombic α-S₈ and polymeric μ-S by SOMs.

Up to now, microbial sulfur metabolism has been widely studied [7], but there have been few publications focused on differential utilization and sulfur speciation transformation of sulfur allotropes [8-14]. These studies indicated that the utilization of sulfur allotropes by different SOMs is quite different. The inherent clue to that, however, is still unclear because of the scarceness of knowledge on utilization of S⁰ allotropes by SOMs. Recently, according our previous description [12], extreme thermophilic Acidianus manzaensis cultured on μ-S grew faster and had higher sulfur oxidation activity than that on α-S₈. Further study showed that μ-S was mostly converted into α-S₈ after A. manzaensis cell growth while α-S₈ was not transformed into another allotrope. After growth of A. manzaensis the surface composition of μ-S was composed of 92.1% α-S₈ and 7.9% μ-S, while no change in composition for α-S₈ was found. However, PENG et al [14] found that μ-S could be more easily bio-adapted and activated than α-S₈ by the Fe²⁺-grown Acidithiobacillus ferrooxidans cells, but had a lower sulfur oxidation activity when this strain has acclimated to the new energy substrate. Meanwhile, HE et al [11] suggested that α-S₈ was activated first and then a part of it might be converted to polymeric sulfur before it was further utilized by the cells. These indicate that not only microbial species but also the culture condition can affect the utilization and sulfur speciation transformation of allotropic forms of S⁰.

In the present study, the utilization of α-S₈ and μ-S by the typically mesophilic strain A. ferrooxidans ATCC 23270, which has acclimated to each energy substrate, was comparatively studied, and the sulfur transformation of these two sulfur allotropes was also investigated by combining the Fourier transforming infrared spectrum (FT-IR) and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy.

2 Experimental

2.1 Strain and culture conditions

The mesophilic strain A. ferrooxidans ATCC 23270 was purchased from American Type Culture Collection (ATCC) and stored at the Key Laboratory of Biometallurgy of Ministry of Education, Central South University, Changsha, China. The basal medium used for cell cultivation was composed of the following components: 3.0 g/L (NH₄)₂SO₄, 0.5 g/L MgSO₄·7H₂O, 0.5 g/L K₂HPO₄, 0.1 g/L KCl, 0.01 g/L Ca(NO₃)₂, adding with α-S₈ (10 g/L) or μ-S (10 g/L) as the energy substrate. The initial pH of the culture medium was adjusted to 1.95 with sulfuric acid. Before the experiment, A. ferrooxidans cells first acclimated to the energy source α-S₈ and μ-S, respectively for several generations’ cultivation, and then inoculated respectively on the corresponding energy substrate α-S₈ and μ-S with initial cell density of 2×10⁷ cell/mL. The culture was incubated in 250 mL Erlenmeyer flasks containing 100 mL culture medium on a rotary shaker at 30 °C and 170 r/min. The abiotic controls were carried out under the same conditions. All experiments were performed in triplicate.

The α-S₈ and μ-S samples used in the present study were prepared according to the previous description [12]. Briefly, for the preparation of μ-S, the purchased polymeric μ-S IS-60 was first continuously stirred in CS₂ (~1 g/mL) for 20 min, let stand for 10 min and then the CS₂ phase was discarded. For the preparation of α-S₈, the purchased analytically pure sublimed orthorhombic sulfur was first sufficiently dissolved in CS₂ (~0.5 g/mL), then the insoluble part was filtered off, and at last the yellow solution was evaporated and crystallized in a fume hood. The purified α-S₈ and μ-S were ground to fine powder with the size of 38-75 mm and stored at 4 °C. The purified α-S₈ and μ-S were characterized by X-ray diffraction and Raman spectroscopy. The XRD patterns and Raman spectra of the original α-S₈ and μ-S were well consistent with the orthorhombic α-S₈ and amorphous μ-S as previously described [12].

2.2 Growth and sulfur oxidation determination

The growth and sulfur oxidation of A. ferrooxidans on α-S₈ or μ-S were evaluated by monitoring the cell density, pH and sulfate concentration of the culture solution at 1 d interval during the cultivation. The cell density was determined by direct counting with a blood corpuscle counter (XB-K-25), the pH was measured with a pH meter (PHS-3C), and the concentration of sulfate ion was determined by barium sulfate turbidimetry [15].

2.3 Sulfur surface morphology and bacterial modification analysis

The surface morphologies of α-S₈ and μ-S samples after utilization by A. ferrooxidans were observed by the scanning electron microscopy (SEM) (Nova^TM NanoSEM 230, FEI, USA). Briefly, the samples were first pre-fixed by 25% formaldehyde overnight, then dehydrated using a graded ethanol series, and at last coated with gold and introduced into the SEM chamber for observation. The bacterial modification of sulfur samples was determined by Fourier transform-infrared (FT-IR) spectroscopy in the range of 4000-500 cm^-1 using an FT-IR spectrometer (Nexus 670, Nicolet, USA).

2.4 Sulfur speciation transformation analysis

The sulfur speciation transformation was analyzed by S K-edge X-ray absorption near edge structure (XANES) spectroscopy, which was performed at soft X-ray beam-line (4B7A beam-line) in Beijing Synchrotron Radiation Facility, China. S K-edge XANES data were recorded in the total electron yield (TEY) model in vacuum and scanned at a step width of 0.3 eV in the region from 2.460 to 2.490 keV. In all cases, the XANES spectra were first normalized to the maximum of the absorption spectrum, and then fitted for their linear combinations using known spectra from “reference samples” (i.e. standard α-S₈ and μ-S) with IFEFFIT program [16,17], where the errors of the fitting results in the software were provided to evaluate the quality of a single fitting.

3 Results and discussion

3.1 Growth and sulfur oxidation of A. ferrooxidans grown on α-S₈ and μ-S

The growth, pH and [SO₄^2-] curves of bacterial cells cultured on α-S₈ and μ-S, and the corresponding growth rate, pH decreasing rate and SO₄^2- production rate curves are shown in Figs. 1 and 2, respectively.

Fig. 1 Growth (a), pH (b) and sulfate concentration (c) curves of A. ferrooxidans cultured with α-S₈ and μ-S, respectively

Fig. 2 Growth rate (a), pH decreasing rate (b) and SO₄^2- production rate (c) curves of A. ferrooxidans cultured with α-S₈ and μ-S, respectively

Results in Fig. 1(a) showed that A. ferrooxidans grown on α-S₈ had longer (about 1 d) lag phase, but reached the earlier (about 1 d) stationary stage and attained the higher maximal cell density than that on μ-S. Results in Fig. 2(a) further showed that cells grown on α-S₈ had a lower growth rate from 1-3 d and a higher growth rate from 3-7 d than that on μ-S, indicating that A. ferrooxidans had a better adaptability on μ-S than that on α-S₈, while better growth on α-S₈ than that on μ-S. S⁰ can be oxidized by sulfur-oxidizing bacteria into SO₄^2- with producing H⁺, resulting in the decrease of pH and the increase of [SO₄^2-]. Results in Figs. 1(b) and (c) showed that, after growth of A. ferrooxidans, the pH value of the culture solution containing α-S₈ was significantly lower and the [SO₄^2-] value of the solution containing α-S₈ was significantly higher than those of the solution containing μ-S, respectively. The pH decreasing rate (Fig. 2(b)) and SO₄^2- production rate (Fig. 2(c)) also showed that, from the 3rd day, the bacterial culture solution containing α-S₈ had higher pH decreasing rate and SO₄^2- production rate than those of the solution containing μ-S. This indicated that after adaption for the energy substrates, A. ferrooxidans cultured on α-S₈ had a higher sulfur oxidation rate than that on μ-S.

The initial stage of the growth and sulfur oxidation of mesophilic A. ferrooxidans grown on α-S₈ and μ-S showed similar results with PENG et al [14]. The latter used the Fe²⁺-grown A. ferrooxidans as the initial incubated cells, and also found that the Fe²⁺-grown A. ferrooxidans cells grew on μ-S faster at initial stage comparing with that on α-S₈.

3.2 Surface morphology and modification of α-S₈ and μ-S after growth of A. ferrooxidans

The surface morphologies (Fig. 3) and the surface modification (Fig. 4) of α-S₈ and μ-S before and after the growth of A. ferrooxidans were examined by SEM and FT-IR spectroscopy, respectively.

Figures 3(b) and (e) showed that the sulfur surfaces for α-S₈ and μ-S in the sterile controls were very slight corrosion by comparison with the original α-S₈ and μ-S (Figs. 3(a) and (d)). However, the surfaces for α-S₈ and μ-S after growth of A. ferrooxidans suffered serious corrosion (Figs. 3(c) and (f)). In addition, the bio-corroded α-S₈ revealed apparently eroding pits on the sample’s surface (Fig. 3(c)), while bio-corroded μ-S was loose and porous. The results indicated that the utilization of α-S₈ by A. ferrooxidans was mostly at sulfur surface level, while the cells produced perforation of μ-S and the interaction between A. ferrooxidans cells and μ-S could be both on the surface and in the interior of this sulfur species.

Fig. 3 Surface morphologies of α-S₈ (a-c) and μ-S (d-f) before and after growth of A. ferrooxidans

Fig. 4 FT-IR spectra of original α-S₈ and μ-S before and after growth of A. ferrooxidans and cells grown on α-S₈ and μ-S, respectively (a), and spectra of α-S₈ and μ-S after growth of A. ferrooxidans at specific wavelength from 1050 to 650 cm^-1 (b)

The bands of the FT-IR spectra of A. ferrooxidans cells (Fig. 4(a)) were assigned according to the previous descriptions [18,19]. The band at 3055-3514 cm^-1 reflected —OH, and protein —NH and —NH₂ groups. The bands at 1622-1658 cm^-1 and near 1550 cm^-1 represented —C=O stretching and —NH₂ vibration, respectively, which always suggested the presence of protein amide group (—CONH—). The bands near 1448 cm^-1 are assigned to —CH₃ and —CH₂ bending vibration. The bands at 1200-1250 cm^-1 and 1040- 1220 cm^-1 are due to C=S and S=O groups, respectively. Compared with the FT-IR spectra of standard α-S₈ and μ-S, the spectra of α-S₈ and μ-S isolated from culture media became much more complex and showed the absorption bands described above, indicating that the surfaces of both α-S₈ and μ-S were modified by the bacterial cells. In addition, according to the previous description [12], the bands at 843 cm^-1 and 876 cm^-1 can be described as the characteristic peaks of α-S₈ and μ-S, respectively. It is worthy to note that the peak at 876 cm^-1 was also found in the spectra of both α-S₈ after growth of A. ferrooxidans and A. ferrooxidans cells cultured on α-S₈, and that the new (shoulder) peaks at 843 cm^-1 appeared in the spectra of both μ-S after growth of A. ferrooxidans and A. ferrooxidans cells cultured on μ-S (Figs. 4(a) and (b)). This indicated that these two S⁰ species can be interconverted by the mesophilic A. ferrooxidans.

3.3 Sulfur speciation transformation of α-S₈ and μ-S after growth of A. ferrooxidans

The sulfur speciation transformation was analyzed by S K-edge XANES spectroscopy, such results are shown in Fig. 5. The S K-edge XANES spectra of original α-S₈ and μ-S showed clear difference in the width and intensity at 2.4727 and 2.4800 keV. The S K-edge XANES spectra of α-S₈ and μ-S in sterile controls and after growth of A. ferrooxidans were analyzed by the linear composition fitting using the spectra of original α-S₈ and μ-S. The fitting results (Table 1) showed that after growth of A. ferrooxidans, the surface composition of amorphous μ-S became 63.1% μ-S and 36.9% α-S₈, while the surface composition of orthorhombic α-S₈ became 68.3% α-S₈ and 31.7% μ-S, which supported the FT-IR results (Fig. 4(b)). In contrast, the surface compositions of α-S₈ and μ-S in the sterile experiment were not changed.

Fig. 5 Normalized sulfur K-edge XANES spectra of standard α-S₈ and μ-S, α-S₈ and μ-S in sterile controls and after growth of A. ferrooxidans

Table 1 Fitted results of S K-edge XANES spectra of measured sample with standard α-S₈ and μ-S spectra (Values in brackets represent errors of fitting results)

In the present study, these two S⁰ allotropes were found to be interconverted by the mesophilic A. ferrooxidans. However, only μ-S was found to be converted to another species after growth of extremely thermophilic A. manzaensis [12] and moderately thermophilic Sulfobacillus thermosulfidooxidans [20]. Results of A. manzaensis showed that bio-corroded μ-S was composed of 92.1% α-S₈ and 7.9% μ-S, while no change in composition for bio-corroded α-S₈ was found [12]. Results of S. thermosulfidooxidans also showed that bio-corroded μ-S began to gradually convert into α-S₈ from the 2nd day when it entered the exponential phase, and the composition finally became 62.3% μ-S and 37.7% α-S₈ on the 4th day at the stationary phase, while no transformation of bio-corroded α-S₈ into μ-S occurred [20]. This indicated that the transformation of sulfur allotropes was also different with different microorganisms. It should be noted that, in the sterile groups, the surface compositions of α-S₈ and μ-S were not changed in the present study (30 °C), which is consistent with the sterile groups at 50 °C. However, at 65 °C the natural transformation of μ-S to the α-S₈ was found. This suggests that different environmental temperatures adopted can also influence the transformation of sulfur allotropes, because α-S₈ is more stable than μ-S and some of μ-S can be converted slowly into α-S₈ at high temperatures [21], as shown in Eq. (1) (short-chain like S_n^2- is a unstable transition state). Furthermore, previous studies demonstrate that this process can be accelerated with the existence of SOMs [12, 14], which is assured by the transformation from μ-S to α-S₈ by A. ferrooxidans even if the ambient temperature (30 °C) is lower than 65 °C.

μ-S→S_n^2-→α-S₈ (n≥1)                         (1)

According to the previous studies concerned on the sulfur metabolism of SOMs [2,22], the utilization of S⁰ can be divided into three steps: 1) extracellular adsorption and activation of sulfur, 2) outer membrane transportation of sulfur, and 3) oxidation of sulfur in the periplasmic space. The extracellular activation was considered to be the rate-limiting step. Previous studies [23,24] indicated that S⁰ (mainly α-S₈) was probably activated by thiol group containing protein(s) by forming —SS_nH (Eq. (2)).

S₈+P—SH→(P—SS₈H)→P—SS_nH, n≥1

(P represents protein, n≥1)                 (2)

Bacterial utilization of μ-S may take the similar mechanism to Eq. (2). With the interaction between μ-S and SOMs, the unstable short-chain like S_n^2- formed in Eq. (1) can be transformed to P—SS_nH by protein —SH group (Eq. (3)). Under the conditions of the growth of A. ferrooxidans, these activated polysulfide compounds can be stored as sulfur globules, which were located either inside or outside the cells with organic groups, containing long sulfur chains terminated with organic groups, sulfur rings (S₈), polysulfides or polythionates, etc [4,25]. Thus, we speculated that α-S₈ could be transformed into μ-S by SOMs as Eq. (2), which could explain why μ-S was detected after utilization of α-S₈ by A. ferrooxidans in the present study. However, the transformation from μ-S to α-S₈ was not found for moderate thermophilic S. thermosulfidooxidans and extreme thermophilic archaea A. manzaensis [12]. This indicated that these different environmental temperatures adopted SOMs might have different activation mechanisms for μ-S and α-S₈.

S_n^2-+P—SH→P—SS_nH                      (3)

4 Conclusions

1) The results of cell growth and sulfur oxidation behavior showed that the strain grown on α-S₈ entered slowly (about 1 d later) into the exponential phase, while grew faster in the exponential phase and attained higher maximal cell density and lower pH value than those on μ-S.

2) After bio-corrosion, both the two sulfur samples were eroded and modified by A. ferrooxidans cells, but α-S₈ was mostly on sulfur surface, while μ-S surface was loose and porous.

3) After growth of A. ferrooxidans, the surface composition of amorphous μ-S became 63.1% μ-S and 36.9% α-S₈, and that of orthorhombic α-S₈ became 68.3% α-S₈ and 31.7% μ-S, indicating that these two elemental sulfur species can be interconverted by the mesophilic A. ferrooxidans.

References

[1] KLAUBER C. A critical review of the surface chemistry of acidic ferric sulphate dissolution of chalcopyrite with regards to hindered dissolution [J]. International Journal of Mineral Processing, 2008, 86(1-4): 1-17.

[2] VERA M, SCHIPPERS A, SAND W. Progress in bioleaching. Part A: Fundamentals and mechanisms of bacterial metal sulfide oxidation [J]. Applied Microbiology and Biotechnology, 2013, 97: 7529-7541.

[3] XIA J L, YANG Y, HE H, ZHAO X J, LIANG C L, ZHENG L, MA C Y, ZHAO Y D, NIE Z Y, QIU G Z. Surface analysis of sulfur speciation on pyrite bioleached by extreme thermophile Acidianus manzaensis using Raman and XANES spectroscopy [J]. Hydrometallurgy, 2010, 100(3-4): 129-135.

[4] KLEINJAN W, KEIZER A, JANSSEN A H, Biologically produced sulfur [C]//Elemental Sulfur and Sulfur-Rich Compounds I. Heidelberg, Berlin: Springer, 2003: 167-188.

[5] ZHANG C G, XIA J L, DING J N, OUYANG X D, NIE Z Y, QIU G Z. Cellular acclimation of Acidithiobacillus ferrooxidans to sulfur bio-oxidation [J]. Minerals and Metallurgical Processing, 2009, 26(1): 30-34.

[6] HARMER S L, THOMAS J E, FORNASIERO D, GERSON A R. The evolution of surface layers formed during chalcopyrite leaching [J]. Geochimica et Cosmochimica Acta, 2006, 70(17): 4392-4402.

[7] DAHL C, FRIEDRICH C G. Microbial sulfur metabolism [M]. Heidelberg, Berlin: Springer, 2008.

[8] LAISHLEY E J, BRYANT R D, KOBRYN B W, HYNE J B. Microcrystalline structure and surface area of elemental sulphur as factors influencing its oxidation by Thiobacillus albertis [J]. Canadian Journal of Microbiology, 1986, 32: 237-242.

[9] BRIAND L E, BONETTO R D, LADAGA J L, DONATI E. Bulk and surface characterization of crystalline and plastic sulphur oxidized by two Thiobacillus species [J]. Process Biochemistry, 1999, 34(3): 249-256.

[10] BLIGHT K R, CANDY R M, RALPH D E. The preferential oxidation of orthorhombic sulfur during batch culture [J]. Hydrometallurgy, 2009, 99(1-2): 100-104.

[11] HE H, XIA J L, HUANG G H, JIANG H C, TAO X X, ZHAO Y D, HE W. Analysis of the elemental sulfur bio-oxidation by Acidithiobacillus ferrooxidans with sulfur K-edge XANES [J]. World Journal of Microbiology and Biotechnology, 2011, 27(8): 1927-1931.

[12] LIU H C, XIA J L, NIE Z Y, PENG A A, MA C Y, ZHENG L, ZHAO Y D. Comparative study of sulfur utilization and speciation transformation of two elemental sulfur species by thermoacidophilic Archaea Acidianus manzaensis YN-25 [J]. Process Biochemistry, 2013, 48(12): 1855-1860.

[13] FRANZ B, LICHTENBERG H, HORMES J, MODROW H, DAHL C, PRANGE A. Utilization of solid ‘elemental’ sulfur by the phototrophic purple sulfur bacterium Allochromatium vinosum: A sulfur K-edge X-ray absorption spectroscopy study [J]. Microbiology, 2007, 153(4): 1268-1274.

[14] PENG An-an, XIA Jin-lan, LIU Hong-chang, NIE Zhen-yuan, YANG Yi, ZHU Wei. Differential utilization of cyclic, orthorhombic α- and chain-like polymeric μ-sulfur by Acidithiobacillus ferrooxidans [J]. Transactions of Nonferrous Metals Society of China, 2014, 24(5): 1562-1570.

[15] PENG A A, LIU H C, NIE Z Y, XIA J L, ZHAO Z D. Improvement of barium sulfate turbidimetry for determination of sulfate concentration in complex bioleaching samples [J]. Journal of Central South University: Science and Technology, 2013, 44(6): 2186-2191. (in Chinese)

[16] PRANGE A. Speciation analysis of microbiologically produced sulfur by X-ray absorption near edge structure spectroscopy [C]// Microbial Sulfur Metabolism. Heidelberg, Berlin: Springer, 2008: 259-272.

[17] RAVEL B, NEWVILLE M. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT [J]. Journal of Synchrotron Radiation, 2005, 12(4): 537-541.

[18] HE Huan, YANG Yi, XIA Jin-lan, DING Jian-nan, ZHAO Xiao-juan, NIE Zhen-yuan. Growth and surface properties of new thermoacidophilic Archaea strain Acidianus manzaensis YN-25 grown on different substrates [J]. Transactions of Nonferrous Metals Society of China, 2008, 18(6): 1374-1378.

[19] PENG An-an, LIU Hong-chang, NIE Zhen-yuan, XIA Jin-lan. Effect of surfactant Tween-80 on sulfur oxidation and expression of sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans [J]. Transactions of Nonferrous Metals Society of China, 2012, 22(12): 3147-3155.

[20] NIE Z Y, LIU H C, XIA J L, ZHU H R, MA C Y, ZHENG L, ZHAO J, QIU G. Differential utilization and transformation of sulfur allotropes, m-S and α-S₈, by moderate thermoacidophile Sulfobacillus thermosulfidooxidans [J]. Research in Microbiology, 2014, 165(8): 639-646.

[21] MEYER B. Elemental sulfur [J]. Chemical Reviews, 1976, 76(3): 367-388.

[22] QUATRINI R, APPIA-AYME C, DENIS Y, JEDLICKI E, HOLMES D S, BONNEFOY V. Extending the models for iron and sulfur oxidation in the extreme acidophile Acidithiobacillus ferrooxidans [J]. BMC Genomics, 2009, 10(1), doi: 10.11861 1471-2164-10-394.

[23] XIA J L, LIU H C, NIE Z Y, PENG A A, ZHEN X J, YANG Y, ZHANG X L. Synchrotron radiation based STXM analysis and micro-XRF mapping of differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on Fe²⁺ and S⁰ [J]. Journal of Microbiological Methods, 2013, 94(3): 257-261.

[24] ROHWERDER T, SAND W. The sulfane sulfur of persulfides is the actual substrate of the sulfur-oxidizing enzymes from Acidithiobacillus and Acidiphilium spp [J]. Microbiology, 2003, 149(7): 1699-1710.

[25] JANSSEN A J H, LETTINGA G, de KEIZER A. Removal of hydrogen sulphide from wastewater and waste gases by biological conversion to elemental sulphur colloidal and interfacial aspects of biologically produced sulphur particles [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999, 151: 389-398.

Acidithiobacillus ferrooxidans适应底物后对两种不同形态单质硫(α-S₈和μ-S)的利用和硫形态转化

刘红昌^1,2，夏金兰^1,2，聂珍媛^1,2，郑 雷³，马陈燕³，赵屹东³

1. 中南大学 资源加工与生物工程学院，长沙 410083；2. 中南大学 生物冶金教育部重点实验室，长沙 410083；

3. 中国科学院 高能物理研究所 北京同步辐射装置，北京 100049

摘  要：研究典型中温嗜酸菌株Acidithiobacillus ferrooxidans ATCC 23270对两种不同形态单质硫(α-S₈和μ-S)的利用和硫形态转化。A. ferrooxidans分别在α-S₈或者μ-S中培养以适应能源底物。A. ferrooxidans在这两种单质硫中的生长和硫氧化行为的结果表明，A. ferrooxidans在α-S₈中生长时比在μ-S中生长晚1 d进入对数期，但是A. ferrooxidans在α-S₈中生长时在对数期生长较快且培养液具有较高的细胞浓度和较低的pH值。经过 A. ferrooxidans的培养，这两种单质硫都被明显腐蚀和细胞修饰。此外，经过A. ferrooxidans的生长，无定型态的μ-S表面组分变为63.1% μ-S和36.9% α-S₈，正交晶系的α-S₈表面组分变为68.3% α-S₈和31.7% μ-S；而无菌对照组μ-S和α-S₈表面组分都没有变化，表明这两种不同形态的单质硫在A. ferrooxidans的作用下发生了相互转化。

关键词：硫利用；硫形态转化；α-S₈；μ-S；Acidithiobacillus ferrooxidans

(Edited by Xiang-qun LI)

Foundation item: Project (51274257) supported by the National Natural Science Foundation of China; Project (U1232103) supported by the Joint Funds of National Natural Science Foundation of China and Large Scientific Facility Foundation of Chinese Academy of Sciences; Project (VR-12419) supported by the Beijing Synchrotron Radiation Facility Public User Program

Corresponding author: Jin-lan XIA; Tel: +86-731-88836944; E-mail: jlxia@csu.edu.cn

DOI: 10.1016/S1003-6326(15)63938-3