Abstract
Background Acidithiobacillus caldus (A. caldus) is widely used in bio-leaching. It gains energy and electrons from oxidation of elemental sulfur and reduced inorganic sulfur compounds (RISCs) for carbon dioxide fixation and growth. Genomic analyses suggest that its sulfur oxidation system involves a truncated sulfur oxidation (Sox) system (omitting SoxCD), non-Sox sulfur oxidation system similar to the sulfur oxidation in A. ferrooxidans, and sulfur oxygenase reductase (SOR). The complexity of the sulfur oxidation system of A. caldus generates a big obstacle on the research of its sulfur oxidation mechanism. However, the development of genetic manipulation method for A. caldus in recent years provides powerful tools for constructing genetic mutants to study the sulfur oxidation system.ResultsAn A. caldus mutant lacking the sulfur oxygenase reductase gene (sor) was created and its growth abilities were measured in media using elemental sulfur (S0) and tetrathionate (K2S4O6) as the substrates, respectively. Then, comparative transcriptome analysis (microarrays and real-time quantitative PCR) of the wild type and the Δsor mutant in S0 and K2S4O6 media were employed to detect the differentially expressed genes involved in sulfur oxidation. SOR was concluded to oxidize the cytoplasmic elemental sulfur, but could not couple the sulfur oxidation with the electron transfer chain or substrate-level phosphorylation. Other elemental sulfur oxidation pathways including sulfur diooxygenase (SDO) and heterodisulfide reductase (HDR), the truncated Sox pathway, and the S4I pathway for hydrolysis of tetrathionate and oxidation of thiosulfate in A. caldus are proposed according to expression patterns of sulfur oxidation genes and growth abilities of the wild type and the mutant in different substrates media.ConclusionAn integrated sulfur oxidation model with various sulfur oxidation pathways of A. caldus is proposed and the features of this model are summarized.
Highlights
Acidithiobacillus caldus (A. caldus), a gram-negative, acidophilic, obligately chemolithotrophic, moderately thermophilic bacterium [1,2] and an important member of a consortium of microorganisms used for industrial bioleaching [3], plays key roles together with iron-oxidizing bacteria in bio-leaching processes [4,5]
The results are shown in Figure 1C: the sor gene region in A. caldus MTH-04 wild type was different from the corresponding region which is replaced by the IS element (ISAtc1) and the transposase gene in the A. caldus MTH-04 mutant
The analysis of the sor regions in different A. caldus strains is depicted in Figure 1C, ISAtc1 is positioned upstream of the sor gene in the wild type A. caldus MTH-04 genome, similar to A. caldus SM-1 but different from A. caldus ATCC 51765, while the sor gene region in the Dsor mutant was replaced by the IS elements
Summary
Acidithiobacillus caldus (A. caldus), a gram-negative, acidophilic, obligately chemolithotrophic, moderately thermophilic bacterium [1,2] and an important member of a consortium of microorganisms used for industrial bioleaching [3], plays key roles together with iron-oxidizing bacteria in bio-leaching processes [4,5]. The sulfur oxidizing (Sox) enzyme system in lithoautotrophic Paracoccus pantotrophus (P. pantotrophus), responsible for the oxidation of sulfide, elemental sulfur, thiosulfate, and sulfite to sulfate, accompanied by electron transfer to cytochrome c, has been well studied [8,9,10,11,12]. It is located in the periplasm and constituted generally by four proteins: SoxYZ, SoxAX, SoxB and Sox(CD)2 [13]. Acidithiobacillus caldus (A. caldus) is widely used in bio-leaching It gains energy and electrons from oxidation of elemental sulfur and reduced inorganic sulfur compounds (RISCs) for carbon dioxide fixation and growth. The development of genetic manipulation method for A. caldus in recent years provides powerful tools for constructing genetic mutants to study the sulfur oxidation system
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
