Sulfur Oxidation in the Acidophilic Autotrophic Acidithiobacillus spp.

Abstract

Sulfur oxidation is an essential component of the earth’s sulfur cycle. Acidithiobacillus spp. can oxidize various reduced inorganic sulfur compounds (RISCs) with high efficiency to obtain electrons for their autotrophic growth. Strains in this genus have been widely applied in bioleaching and biological desulfurization. Diverse sulfur-metabolic pathways and corresponding regulatory systems have been discovered in these acidophilic sulfur-oxidizing bacteria. The sulfur-metabolic enzymes in Acidithiobacillus spp. can be categorized as elemental sulfur oxidation enzymes (sulfur dioxygenase, sulfur oxygenase reductase, and Hdr-like complex), enzymes in thiosulfate oxidation pathways (tetrathionate intermediate thiosulfate oxidation (S4I) pathway, the sulfur oxidizing enzyme (Sox) system and thiosulfate dehydrogenase), sulfide oxidation enzymes (sulfide:quinone oxidoreductase) and sulfite oxidation pathways/enzymes. The two-component systems (TCSs) are the typical regulation elements for periplasmic thiosulfate metabolism in these autotrophic sulfur-oxidizing bacteria. Examples are RsrS/RsrR responsible for S4I pathway regulation and TspS/TspR for Sox system regulation. The proposal of sulfur metabolic and regulatory models provide new insights and overall understanding of the sulfur-metabolic processes in Acidithiobacillus spp. The future research directions and existing barriers in the bacterial sulfur metabolism are also emphasized here and the breakthroughs in these areas will accelerate the research on the sulfur oxidation in Acidithiobacillus spp. and other sulfur oxidizers.

Determinants of sulphur chemolithoautotrophy in the extremely thermoacidophilic Sulfolobales

“…The initial premise was that S. acidocaldarius DSM639 was at some point an autotrophic sulphur oxidizer, and therefore minimal changes (provision of two known sulphur‐oxidation enzymes that were missing) would be required to recover that capability. While chemolithoautotrophy was not restored, increased sulphur oxidation by both RK06 and RK34 strains supports the SOR‐centric model of sulphur oxidation in the Sulfolobales , instead of the ‘recycle’ model proposed for Acidithiobacillus caldus (Chen et al ., ; Wang et al ., ). It is also interesting that, at least in the Sulfolobales genomes sequenced so far, SOR is never found without TQO (Fig.…”

“…The supplementary, non‐essential role of SOR in the S 0 oxidation pathways of Acidith. caldus differs from current models of sulphur oxidation in the Sulfolobales , raising the question of whether SOR plays different metabolic roles in sulphur‐oxidizing bacteria and archaea (Wang et al ., ). This issue was addressed here by examining the role of SOR in Sulfolobales species that natively either oxidize sulphur ( Acidianus brierleyi ) or likely had this metabolic capability in their evolutionary history ( S. acidocaldarius DSM639).…”

Integration of Biological Networks for Acidithiobacillus thiooxidans Describes a Modular Gene Regulatory Organization of Bioleaching Pathways

“…This regulator is known as a master regulator of genes encoding for proteins involved in sulfur metabolism, particularly, its assimilation (van der Ploeg et al, 2001) and also iron starvation (Imperi et al, 2010). For A. thiooxidans species, sulfur metabolism plays a crucial role in the acquisition of electrons for their autotrophic growth (Wang et al, 2018).…”

“…Moreover, RISC oxidation is a complex process whose associated metabolic pathways have not being fully elucidated to date. Different pathways have been proposed for the Acidithiobacillus species (Wang et al, 2018) including a pathway that involves the assimilation enzymes APS kinase and PAPS reductase (Yin et al, 2014). Based on these considerations sulfur assimilation metabolic pathways were also considered in this analysis (pink pathways in Figure 2).…”

Heterozygous, polyploid, giant bacterium,Achromatium, possesses an identical functional inventory worldwide across drastically different ecosystems

“…5). It contains among others a sulfur transferase, another 202 type of enzyme known to be involved in sulfur oxidation (Wang et al 2019). Cluster 2 contains the 203 largest number of genes most of which are involved in the central metabolism of the cell (Fig.5).…”