Ferriphaselus amnicola strain GF-20, a new iron- and thiosulfate-oxidizing bacterium isolated from a hard rock aquifer.

Ferriphaselus amnicola GF-20 is the first Fe-oxidizing bacterium isolated from the continental subsurface. It was isolated from groundwater circulating at 20 m depth in the fractured-rock catchment observatory of Guidel-Ploemeur (France). Strain GF-20 is a neutrophilic, iron- and thiosulfate-oxidizer and grows autotrophically. The strain shows a preference for low oxygen concentrations, which suggests an adaptation to the limiting oxygen conditions of the subsurface. It produces extracellular stalks and dreads when grown with Fe(II) but does not secrete any structure when grown with thiosulfate. Phylogenetic analyses and genome comparisons revealed that strain GF-20 is affiliated with the species F. amnicola and is strikingly similar to F. amnicola strain OYT1, which was isolated from a groundwater seep in Japan. Based on the phenotypic and phylogenetic characteristics, we propose that GF-20 represents a new strain within the species F. amnicola.

YeeD is an essential partner for YeeE-mediated thiosulfate uptake in bacteria and regulates thiosulfate ion decomposition.

Uptake of thiosulfate ions as an inorganic sulfur source from the environment is important for bacterial sulfur assimilation. Recently, a selective thiosulfate uptake pathway involving a membrane protein YeeE (TsuA) in Escherichia coli was characterized. YeeE-like proteins are conserved in some bacteria, archaea, and eukaryotes. However, the precise function of YeeE, along with its potential partner protein in the thiosulfate ion uptake pathway, remained unclear. Here, we assessed selective thiosulfate transport via Spirochaeta thermophila YeeE in vitro and characterized E. coli YeeD (TsuB) as an adjacent and essential protein for YeeE-mediated thiosulfate uptake in vivo. We further showed that S. thermophila YeeD possesses thiosulfate decomposition activity and that a conserved cysteine in YeeD was modified to several forms in the presence of thiosulfate. Finally, the crystal structures of S. thermophila YeeE-YeeD fusion proteins at 3.34-Å and 2.60-Å resolutions revealed their interactions. The association was evaluated by a binding assay using purified S. thermophila YeeE and YeeD. Based on these results, a model of the sophisticated uptake of thiosulfate ions by YeeE and YeeD is proposed.

Rates of iron(III) reduction coupled to elemental sulfur or tetrathionate oxidation by acidophilic microorganisms and detection of sulfur intermediates.

Bioleaching processes and acid mine drainage (AMD) generation are mainly driven by aerobic microbial iron(II) and inorganic sulfur/compound oxidation. Dissimilatory iron(III) reduction coupled to sulfur/compound oxidation (DIRSO) by acidophilic microorganisms has been described for anaerobic cultures, but iron reduction was observed under aerobic conditions as well. Aim of this study was to explore reaction rates and mechanisms of this process. Cell-specific iron(III) reduction rates for different Acidithiobacillus (At.) strains during batch culture growth or stationary phase with iron(III) (∼40 mM) as electron acceptor and elemental sulfur or tetrathionate as electron donor (1% or 5 mM, respectively) were determined. The rates were highest under anaerobic conditions for the At. ferrooxidans type strain with 6.8 × 106 and 1.1 × 107 reduced iron(III) ions per second per cell for growth on elemental sulfur and tetrathionate, respectively. The iron(III) reduction rates were somehow lower for the anaerobically sulfur grown archaeon Ferroplasma acidiphilum, and lowest for the sulfur grown At. caldus type strain under aerobic conditions (1.7 × 106 and 7.3 × 104 reduced iron(III) ions per second per cell, respectively). The rates for five strains of At. thiooxidans (aerobe) were in between those for At. ferrooxidans (anaerobe) and At. caldus (aerobe). There was no pronounced pH dependence of iron(III) reduction rates in the range of pH 1.0-1.9 for the type strains of all species but rates increased with increasing pH for four other At. thiooxidans strains. Thiosulfate as sulfur intermediate was found for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III) but not during anaerobic growths on elemental sulfur and iron(III), and a small concentration was measured during aerobic growths on tetrathionate without iron(III). For the At. thiooxidans type strain thiosulfate was found with tetrathionate grown cells under aerobic conditions in presence and absence of iron(III), but not with sulfur grown cells. Evidence for hydrogen sulfide production at low pH was found for the At. ferrooxidans as well as the At. thiooxidans type strains during microaerophilic growth on elemental sulfur and for At. ferrooxidans during anaerobic growths on tetrathionate and iron(III). The occurrence of sulfur compound intermediates supports the hypothesis that chemical reduction of iron(III) ions takes place by sulfur compounds released by the microbial cells.

Reaction of Thiosulfate Dehydrogenase with a Substrate Mimic Induces Dissociation of the Cysteine Heme Ligand Giving Insights into the Mechanism of Oxidative Catalysis.

Thiosulfate dehydrogenases are bacterial cytochromes that contribute to the oxidation of inorganic sulfur. The active sites of these enzymes contain low-spin c-type heme with Cys-/His axial ligation. However, the reduction potentials of these hemes are several hundred mV more negative than that of the thiosulfate/tetrathionate couple (Em, +198 mV), making it difficult to rationalize the thiosulfate oxidizing capability. Here, we describe the reaction of Campylobacter jejuni thiosulfate dehydrogenase (TsdA) with sulfite, an analogue of thiosulfate. The reaction leads to stoichiometric conversion of the active site Cys to cysteinyl sulfonate (Cα-CH2-S-SO3-) such that the protein exists in a form closely resembling a proposed intermediate in the pathway for thiosulfate oxidation that carries a cysteinyl thiosulfate (Cα-CH2-S-SSO3-). The active site heme in the stable sulfonated protein displays an Em approximately 200 mV more positive than the Cys-/His-ligated state. This can explain the thiosulfate oxidizing activity of the enzyme and allows us to propose a catalytic mechanism for thiosulfate oxidation. Substrate-driven release of the Cys heme ligand allows that side chain to provide the site of substrate binding and redox transformation; the neighboring heme then simply provides a site for electron relay to an appropriate partner. This chemistry is distinct from that displayed by the Cys-ligated hemes found in gas-sensing hemoproteins and in enzymes such as the cytochromes P450. Thus, a further class of thiolate-ligated hemes is proposed, as exemplified by the TsdA centers that have evolved to catalyze the controlled redox transformations of inorganic oxo anions of sulfur.

Rhodaneses minimize the accumulation of cellular sulfane sulfur to avoid disulfide stress during sulfide oxidation in bacteria.

Heterotrophic bacteria and human mitochondria often use sulfide: quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO) to oxidize sulfide to sulfite and thiosulfate. Bioinformatic analysis showed that the genes encoding RHOD domains were widely presented in annotated sqr-pdo operons and grouped into three types: fused with an SQR domain, fused with a PDO domain, and dissociated proteins. Biochemical evidence suggests that RHODs facilitate the formation of thiosulfate and promote the reaction between inorganic polysulfide and glutathione to produce glutathione polysulfide. However, the physiological roles of RHODs during sulfide oxidation by SQR and PDO could only be tested in an RHOD-free host. To test this, 8 genes encoding RHOD domains in Escherichia coli MG1655 were deleted to produce E. coli RHOD-8K. The sqrCp and pdoCp genes from Cupriavidus pinatubonensis JMP134 were cloned into E. coli RHOD-8K. SQRCp contains a fused RHOD domain at the N-terminus. When the fused RHOD domain of SQRCp was inactivated, the cells oxidized sulfide into increased thiosulfate with the accumulation of cellular sulfane sulfur in comparison with cells containing the intact sqrCp and pdoCp. The complementation of dissociated DUF442 minimized the accumulation of cellular sulfane sulfur and reduced the production of thiosulfate. Further analysis showed that the fused DUF442 domain modulated the activity of SQRCp and prevented it from directly passing the produced sulfane sulfur to GSH. Whereas, the dissociated DUF442 enhanced the PDOCp activity by several folds. Both DUF442 forms minimized the accumulation of cellular sulfane sulfur, which spontaneously reacted with GSH to produce GSSG, causing disulfide stress during sulfide oxidation. Thus, RHODs may play multiple roles during sulfide oxidation.

Hydrogen Sulfide Metabolite, Sodium Thiosulfate: Clinical Applications and Underlying Molecular Mechanisms.

Thiosulfate in the form of sodium thiosulfate (STS) is a major oxidation product of hydrogen sulfide (H2S), an endogenous signaling molecule and the third member of the gasotransmitter family. STS is currently used in the clinical treatment of acute cyanide poisoning, cisplatin toxicities in cancer therapy, and calciphylaxis in dialysis patients. Burgeoning evidence show that STS has antioxidant and anti-inflammatory properties, making it a potential therapeutic candidate molecule that can target multiple molecular pathways in various diseases and drug-induced toxicities. This review discusses the biochemical and molecular pathways in the generation of STS from H2S, its clinical usefulness, and potential clinical applications, as well as the molecular mechanisms underlying these clinical applications and a future perspective in kidney transplantation.

Defect of RNA pyrophosphohydrolase RppH enhances fermentative production of L-cysteine in Escherichia coli.

Fermentative production of L-cysteine has been established using Escherichia coli. In that procedure, thiosulfate is a beneficial sulfur source, whereas repressing sulfate utilization. We first found that thiosulfate decreased transcript levels of genes related to sulfur assimilation, particularly whose expression is controlled by the transcription factor CysB. Therefore, a novel approach, i.e. increment of expression of genes involved in sulfur-assimilation, was attempted for further improvement of L-cysteine overproduction. Disruption of the rppH gene significantly augmented transcript levels of the cysD, cysJ, cysM and yeeE genes (≥1.5-times) in medium containing sulfate as a sole sulfur source, probably because the rppH gene encodes mRNA pyrophosphohydrolase that triggers degradation of certain mRNAs. In addition, the ΔrppH strain appeared to preferentially uptake thiosulfate rather than sulfate, though thiosulfate dramatically reduced expression of the known sulfate/thiosulfate transporter complexes in both ΔrppH and wild-type cells. We also found that both YeeE and YeeD are required for the strain without the transporters to grow in the presence of thiosulfate as a sole sulfur source. Therefore, yeeE and yeeD are assigned as genes responsible for thiosulfate uptake (tsuA and tsuB, respectively). In final, we applied the ΔrppH strain to the fermentative production of L-cysteine. Disruption of the rppH gene enhanced L-cysteine biosynthesis, as a result, a strain producing approximately twice as much L-cysteine as the control strain was obtained.

Metabolism of Sulfur-Containing Amino Acids: How the Body Copes with Excess Methionine, Cysteine, and Sulfide.

Metabolism of excess methionine (Met) to homocysteine (Hcy) by transmethylation is facilitated by the expression of methionine adenosyltransferase (MAT) I/III and glycine N-methyltransferase (GNMT) in liver, and a lack of either enzyme results in hypermethioninemia despite normal concentrations of MATII and methyltransferases other than GNMT. The further metabolism of Hcy by the transsulfuration pathway is facilitated by activation of cystathionine ß-synthase (CBS) by S-adenosylmethionine (SAM) as well as the relatively high KM of CBS for Hcy. Transmethylation plus transsulfuration effects catabolism of the Met molecule along with transfer of the sulfur atom of Met to serine to synthesize cysteine (Cys). Oxidation and excretion of Met sulfur depend upon Cys catabolism and sulfur oxidation pathways. Excess Cys is oxidized by cysteine dioxygenase 1 (CDO1) and further metabolized to taurine or sulfate. Some Cys is normally metabolized by desulfhydration pathways, and the hydrogen sulfide (H2S) produced is further oxidized to sulfate. If Cys or Hcy concentrations are elevated, Cys or Hcy desulfhydration can result in excess H2S and thiosulfate production. Excess Cys or Met may also promote their limited metabolism by transamination pathways.

Limnobacter alexandrii sp. nov., a thiosulfate-oxidizing, heterotrophic and EPS-bearing Burkholderiaceae isolated from cultivable phycosphere microbiota of toxic Alexandrium catenella LZT09.

A novel Gram-negative, aerobic, motile and short rod-shaped bacterium with exopolysaccharides production, designated as LZ-4T, was isolated from cultivable phycosphere microbiota of harmful algal blooms-causing marine dinoflagellate Alexandrium catenella LZT09 which produces paralytic shellfish poisoning toxins. Strain LZ-4T was able to use thiosulfate (optimum concentration 10 mM) as energy source for bacterial growth. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain LZ-4T belonged to the genus Limnobacter, showing high 16S rRNA gene sequences similarities with L. thiooxidans DSM 13612T (99.4%), L. humi NBRC 11650T (98.2%) and L. litoralis NBRC 105857T (97.2%), respectively. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between LZ-4T and L. thiooxidans DSM 13612T were 78.9 and 21.9%, respectively. Both values were far lower than the thresholds (95-96% for ANI and 70% for dDDH) generally accepted for new species delineation. The respiratory quinone of strain LZ-4T was Q-8. The dominant cellular fatty acids were determined as summed feature 3 (C16:1 ω6c/ω7c), summed feature 8 (C18:1 ω6c/ω7c) and C16:0. Polar lipids profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids and three unidentified polar lipids. The genomic DNA G+C content of strain LZ-4T was 52.5 mol%. Based on polyphasic characterization, strain LZ-4T represents a novel species of the genus Limnobacter, for which the name Limnobacter alexandrii sp. nov. is proposed. The type strain is LZ-4T (=CCTCC AB 2019004T =KCTC 72281T).

Molecular mechanism of sulfur chemolithotrophy in the betaproteobacterium Pusillimonas ginsengisoli SBSA.

Chemolithotrophic sulfur oxidation represents a significant part of the biogeochemical cycling of this element. Due to its long evolutionary history, this ancient metabolism is well known for its extensive mechanistic and phylogenetic diversification across a diverse taxonomic spectrum. Here we carried out whole-genome sequencing and analysis of a new betaproteobacterial isolate, Pusillimonas ginsengisoli SBSA, which is found to oxidize thiosulfate via the formation of tetrathionate as an intermediate. The 4.7 Mb SBSA genome was found to encompass a soxCDYZAXOB operon, plus single thiosulfate dehydrogenase (tsdA) and sulfite : acceptor oxidoreductase (sorAB) genes. Recombination-based knockout of tsdA revealed that the entire thiosulfate is first converted to tetrathionate by the activity of thiosulfate dehydrogenase (TsdA) and the Sox pathway is not functional in this bacterium despite the presence of all necessary sox genes. The ∆soxYZ and ∆soxXA knockout mutants exhibited a wild-type-like phenotype for thiosulfate/tetrathionate oxidation, whereas ∆soxB, ∆soxCD and soxO::KanR mutants only oxidized thiosulfate up to tetrathionate intermediate and had complete impairment in tetrathionate oxidation. The substrate-dependent O2 consumption rate of whole cells and the sulfur-oxidizing enzyme activities of cell-free extracts, measured in the presence/absence of thiol inhibitors/glutathione, indicated that glutathione plays a key role in SBSA tetrathionate oxidation. The present findings collectively indicate that the potential glutathione : tetrathionate coupling in P. ginsengisoli involves a novel enzymatic component, which is different from the dual-functional thiol dehydrotransferase (ThdT), while subsequent oxidation of the sulfur intermediates produced (e.g. glutathione : sulfodisulfane molecules) may proceed via the iterative action of soxBCD .

Mycobacterium tuberculosis CysA2 is a dual sulfurtransferase with activity against thiosulfate and 3-mercaptopyruvate and interacts with mammalian cells.

Cyanide is a toxic compound that is converted to the non-toxic thiocyanate by a rhodanese enzyme. Rhodaneses belong to the family of transferases (sulfurtransferases), which are largely studied. The sulfur donor defines the subfamily of these enzymes as thiosulfate:cyanide sulfurtransferases or rhodaneses (TSTs) or 3-mercaptopyruvate sulfurtransfeases (MSTs). In Mycobacterium tuberculosis, the causative agent of tuberculosis, the gene Rv0815c encodes the protein CysA2, a putative uncharacterized thiosulfate:cyanide sulfurtransferase that belongs to the essential sulfur assimilation pathway in the bacillus and is secreted during infection. In this work, we characterized the functional and structural properties of CysA2 and its kinetic parameters. The recombinant CysA2 is a α/ß protein with two rhodanese-like domains that maintains the functional motifs and a catalytic cysteine. Sulfurtransferase activity was determined using thiosulfate and 3-mercaptopyruvate as sulfur donors. The assays showed Km values of 2.89 mM and 7.02 mM for thiosulfate and 3-mercaptopyruvate, respectively, indicating the protein has dual activity as TST and MST. Immunological assays revealed that CysA2 interacted with pulmonary cells, and it was capable to activate macrophages and dendritic cells, indicating the stimulation of the immune response, which is important for its use as an antigen for vaccine development and immunodiagnostic.

Mental retardation in Down syndrome: Two ways to treat.

Mental retardation is a progressive condition in Down syndrome: intelligence starts to decline linearly within the first year. This phenomenon could be related to the overproduction of a toxic compound, hydrogen sulfide. Indeed, a gene located on chromosome 21 controls the production of cystathionine-ß-synthase, an enzyme involved in hydrogen sulfide production in the central nervous system. It has recently been demonstrated that excess cystathionine-ß-synthase levels are needed and sufficient to induce cognitive phenotypes in mouse models of Down syndrome. Thus, two therapeutic options might be used in Down syndrome patients: the use of a specific cystathionine ß-synthase inhibitor and the use of an effective antidote to reduce hydrogen sulfide toxicity. Prenatal treatment of Down syndrome fetuses is also suggested.

Sodium thiosulfate enhances production of polysaccharides and anticancer activities of sulfated polysaccharides in Antrodia cinnamomea.

Sulfated polysaccharides (SPSs) are polysaccharides (PSs) with high sulfate functionalization and possess bioactivities. This study aimed to increase the sulfate content of SPSs in Antrodia cinnamomea through sulfate feeding. Feeding A. cinnamomea with sodium thiosulfate was found to increase yields of PSs and SPSs in A. cinnamomea. The SPSs thus obtained (ST-SPS) were further isolated, showing enhanced sulfate content of 2.5 mmol/g. Sodium thiosulfate induced changes in molecular weight from 320 kDa to 1342 kDa, and area percentage of low-molecular-weight ST-SPS (< 20 kDa) was decreased. Functional studies revealed that sodium thiosulfate increased the ST-SPS anticancer efficacy in cancer cells via inhibition of EGFR/AKT signaling. Moreover, the ST-SPS enhanced synergistically cisplatin-, gefitinib- and 5 FU-induced cytotoxic effects in lung cancer H1975 cells and colon cancer CT26 cells. This study is the first to demonstrate that sodium thiosulfate induced changes in properties of A. cinnamomea with the anticancer mechanisms of ST-SPS.

Effects of Thiosulfate as a Sulfur Source on Plant Growth, Metabolites Accumulation and Gene Expression in Arabidopsis and Rice.

Plants are considered to absorb sulfur from their roots in the form of sulfate. In bacteria like Escherichia coli, thiosulfate is a preferred sulfur source. It is converted into cysteine (Cys). This transformation consumes less NADPH and ATP than sulfate assimilation into Cys. In Saccharomyces cerevisiae, thiosulfate promoted growth more than sulfate. In the present study, the availability of thiosulfate, the metabolite transformations and gene expressions it induces were investigated in Arabidopsis and rice as model dicots and monocots, respectively. In Arabidopsis, the thiosulfate-amended plants had lower biomass than those receiving sulfate when sulfur concentrations in the hydroponic medium were above 300 µM. In contrast, rice biomass was similar for plants raised on thiosulfate and sulfate at 300 µM sulfur. Therefore, both plants can use thiosulfate but it is a better sulfur source for rice. In both plants, thiosulfate levels significantly increased in roots following thiosulfate application, indicating that the plants absorbed thiosulfate into their root cells. Thiosulfate is metabolized in plants by a different pathway from that used for sulfate metabolism. Thiosulfate increases plant sulfide and cysteine persulfide levels which means that plants are in a more reduced state with thiosulfate than with sulfate. The microarray analysis of Arabidopsis roots revealed that 13 genes encoding Cys-rich proteins were upregulated more with thiosulfate than with sulfate. These results together with those of the widely targeted metabolomics analysis were used to proposes a thiosulfate assimilation pathway in plants.

Generation of hydrogen sulfide from sulfur assimilation in Escherichia coli.

Many organisms produce endogenous hydrogen sulfide (H2S) as a by-product of protein, peptide, or L-cysteine degradation. Recent reports concerning mammalian cells have demonstrated that H2S acts as a signaling molecule playing important roles in various biological processes. In contrast to mammals, bacterial H2S signaling remains unclear. In this work, we demonstrate that Escherichia coli generates H2S through the assimilation of inorganic sulfur, without L-cysteine degradation. Comparison of phenotypes and genomes between laboratory E. coli K-12 strains revealed a major contribution of CRP (a protein that controls the expression of numerous genes involved in glycolysis) to H2S generation. We found that H2S was produced by cells growing in a synthetic minimal medium containing thiosulfate as a sole inorganic sulfur source, but not in a medium only containing sulfate. Furthermore, E. coli generated H2S in a CRP-dependent manner as a response to glucose starvation. These results indicate that CRP plays a key role in the generation of H2S coupled to thiosulfate assimilation, whose molecular mechanisms remains to be elucidated. Here, we propose a potential biological role of the H2S as a signaling mediator for a cross-talk between carbon and sulfur metabolism in E. coli.

Reductive dissolution and sequestration of arsenic by microbial iron and thiosulfate reduction.

Iron oxide and oxy-hydroxide are commonly used for remediation and rehabilitation of arsenic (As)-contaminated soil and water. However, the stability of As sequestered by iron oxide and oxy-hydroxide under anaerobic conditions is still uncertain. Geochemical properties influence the behavior of As; in addition, microbial activities affect the mobility of sequestered As in soil and water. Microbial-mediated iron reduction can increase the mobility of As by reductive dissolution of Fe oxide; however, microbial-mediated sulfate reduction can decrease the mobility of As by sulfide mineral precipitation. This study investigated the geomicrobial impact on the behavior of As and stability of sequestered As in iron-rich sediment under anaerobic conditions. Increase in Fe(II) concentrations in water was evidence of microbial-mediated iron reduction. Arsenic concentrations increased with Fe(II) concentration; however, the thiosulfate reduction process also induced immobilization of As through the precipitation of AsFeS. Therefore, microbial-mediated iron reduction and thiosulfate reduction have opposite influences on the mobility of As under anaerobic condition.

Cysteine biosynthesis in Neisseria species.

The principal mechanism of reducing sulfur into organic compounds is via the synthesis of l-cysteine. Cysteine is used for protein and glutathione synthesis, as well as being the primary sulfur source for a variety of other molecules, such as biotin, coenzyme A, lipoic acid and more. Glutathione and other cysteine derivatives are important for protection against the oxidative stress that pathogenic bacteria such as Neisseria gonorrhoeae and Neisseria meningitidis encounter during infection. With the alarming rise of antibiotic-resistant strains of N. gonorrhoeae, the development of inhibitors for the future treatment of this disease is critical, and targeting cysteine biosynthesis enzymes could be a promising approach for this. Little is known about the transport of sulfate and thiosulfate and subsequent sulfate reduction and incorporation into cysteine in Neisseria species. In this review we investigate cysteine biosynthesis within Neisseria species and examine the differences between species and with other bacteria. Neisseria species exhibit different arrangements of cysteine biosynthesis genes and have slight differences in how they assimilate sulfate and synthesize cysteine, while, most interestingly, N. gonorrhoeae by virtue of a genome deletion, lacks the ability to reduce sulfate to bisulfide for incorporation into cysteine, and as such uses the thiosulfate uptake pathway for the synthesis of cysteine.

Thermus sediminis sp. nov., a thiosulfate-oxidizing and arsenate-reducing organism isolated from Little Hot Creek in the Long Valley Caldera, California.

Thermus species are widespread in natural and artificial thermal environments. Two new yellow-pigmented strains, L198T and L423, isolated from Little Hot Creek, a geothermal spring in eastern California, were identified as novel organisms belonging to the genus Thermus. Cells are Gram-negative, rod-shaped, and non-motile. Growth was observed at temperatures from 45 to 75 °C and at salinities of 0-2.0% added NaCl. Both strains grow heterotrophically or chemolithotrophically by oxidation of thiosulfate to sulfate. L198T and L423 grow by aerobic respiration or anaerobic respiration with arsenate as the terminal electron acceptor. Values for 16S rRNA gene identity (≤ 97.01%), digital DNA-DNA hybridization (≤ 32.7%), OrthoANI (≤ 87.5%), and genome-to-genome distance (0.13) values to all Thermus genomes were less than established criteria for microbial species. The predominant respiratory quinone was menaquinone-8 and the major cellular fatty acids were iso-C15:0, iso-C17:0 and anteiso-C15:0. One unidentified phospholipid (PL1) and one unidentified glycolipid (GL1) dominated the polar lipid pattern. The new strains could be differentiated from related taxa by ß-galactosidase and ß-glucosidase activity and the presence of hydroxy fatty acids. Based on phylogenetic, genomic, phenotypic, and chemotaxonomic evidence, the novel species Thermus sediminis sp. nov. is proposed, with the type strain L198T (= CGMCC 1.13590T = KCTC XXX).

The Complete Pathway for Thiosulfate Utilization in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is known to grow with thiosulfate as a sulfur source, and it produces more ethanol when using thiosulfate than using sulfate. Here, we report how it assimilates thiosulfate. S. cerevisiae absorbed thiosulfate into the cell through two sulfate permeases, Sul1 and Sul2. Two rhodaneses, Rdl1 and Rdl2, converted thiosulfate to a persulfide and sulfite. The persulfide was reduced by cellular thiols to H2S, and sulfite was reduced by sulfite reductase to H2S. Cysteine synthase incorporated H2S into O-acetyl-l-homoserine to produce l-homocysteine, which is the precursor for cysteine and methionine in S. cerevisiae Several other rhodaneses replaced Rdl1 and Rdl2 for thiosulfate utilization in the yeast. Thus, any organisms with the sulfate assimilation system potentially could use thiosulfate as a sulfur source, since rhodaneses are common in most organisms.IMPORTANCE The complete pathway of thiosulfate assimilation in baker's yeast is determined. The finding reveals the extensive overlap between sulfate and thiosulfate assimilation. Rhodanese is the only additional enzyme for thiosulfate utilization. The common presence of rhodanese in most organisms, including Bacteria, Archaea, and Eukarya, suggests that most organisms with the sulfate assimilation system also use thiosulfate. Since it takes less energy to reduce thiosulfate than sulfate for assimilation, thiosulfate has the potential to become a choice of sulfur in optimized media for industrial fermentation.

Ciceribacter thiooxidans sp. nov., a novel nitrate-reducing thiosulfate-oxidizing bacterium isolated from sulfide-rich anoxic sediment.

Two facultative chemolithotrophic, nitrate-reducing thiosulfate-oxidizing strains, F43bT and F21, were isolated from the sulfide-rich anoxic sediment of an urban creek in Pearl River Delta, China. Both strains were Gram-negative, facultatively anaerobic, non-spore-forming and rod-shaped with a flagellum. Phylogenetic analyses of 16S rRNA genes and the thrC, recA, glnII and atpD housekeeping genes revealed that the type strain shared high sequence similarities to Ciceribacter lividus MSSRFBL1T, with 98.8, 90.9, 94.8, 95.4 and 96.1 % identity, respectively. In addition, the major isoprenoid quinone (ubiquinone Q-10) and the DNA G+C content (66.0 mol%) of the type strain were similar to those of Ciceribacter lividus MSSRFBL1T. These results strongly support the classification of strains F43bT and F21 into the genus Ciceribacter. However, these strains diverged markedly from strain MSSRFBL1T with respect to several physiological and biochemical properties such as their semi-translucent colonies and nitrate-reducing and simultaneous thiosulfate-oxidizing respiration. Furthermore, the predominant fatty acids of strain F43bT were summed feature 2 (C18 : 1ω9t and/or C18 : 1ω9c and/or C18 : 1ω11t), C14 : 0 3-OH, C18 : 0 and C16 : 0, and its polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidymonomethylethanolamine and an unidentified glycolipid, which represented another two significant differences from strain MSSRFBL1T. Importantly, the DNA-DNA relatedness between strain F43bT and MSSRFBL1T was only 47.7 %. Based on the aforementioned polyphasic taxonomic results, the two isolates are suggested to represent a novel species of the genus Ciceribacter, for which the name Ciceribacterthiooxidans sp. nov. is proposed; the type strain is F43bT (=CCTCC AB 2016062T=KCTC 52231T).