Thioredoxin targets fundamental processes in a methane-producing archaeon, Methanocaldococcus jannaschii

Catalytic Activity of the Archetype from Group 4 of the FTR-like Ferredoxin:Thioredoxin Reductase Family Is Regulated by Unique S = 7/2 and S = 1/2 [4Fe-4S] Clusters

Thioredoxin reductases (TrxR) activate thioredoxins (Trx) that regulate the activity of diverse target proteins essential to prokaryotic and eukaryotic life. However, very little is understood of TrxR/Trx systems and redox control in methanogenic microbes from the domain Archaea (methanogens), for which genomes are abundant with annotations for ferredoxin:thioredoxin reductases [Fdx/thioredoxin reductase (FTR)] from group 4 of the widespread FTR-like family. Only two from the FTR-like family are characterized: the plant-type FTR from group 1 and FDR from group 6. Herein, the group 4 archetype (AFTR) from Methanosarcina acetivorans was characterized to advance understanding of the family and TrxR/Trx systems in methanogens. The modeled structure of AFTR, together with EPR and Mössbauer spectroscopies, supports a catalytic mechanism similar to plant-type FTR and FDR, albeit with important exceptions. EPR spectroscopy of reduced AFTR identified a transient [4Fe-4S]1+ cluster exhibiting a mixture of S = 7/2 and typical S = 1/2 signals, although rare for proteins containing [4Fe-4S] clusters, it is most likely the on-pathway intermediate in the disulfide reduction. Furthermore, an active site histidine equivalent to residues essential for the activity of plant-type FTR and FDR was found dispensable for AFTR. Finally, a unique thioredoxin system was reconstituted from AFTR, ferredoxin, and Trx2 from M. acetivorans, for which specialized target proteins were identified that are essential for growth and other diverse metabolisms.

Evolving understanding of rumen methanogen ecophysiology

Production of methane by methanogenic archaea, or methanogens, in the rumen of ruminants is a thermodynamic necessity for microbial conversion of feed to volatile fatty acids, which are essential nutrients for the animals. On the other hand, methane is a greenhouse gas and its production causes energy loss for the animal. Accordingly, there are ongoing efforts toward developing effective strategies for mitigating methane emissions from ruminant livestock that require a detailed understanding of the diversity and ecophysiology of rumen methanogens. Rumen methanogens evolved from free-living autotrophic ancestors through genome streamlining involving gene loss and acquisition. The process yielded an oligotrophic lifestyle, and metabolically efficient and ecologically adapted descendants. This specialization poses serious challenges to the efforts of obtaining axenic cultures of rumen methanogens, and consequently, the information on their physiological properties remains in most part inferred from those of their non-rumen representatives. This review presents the current knowledge of rumen methanogens and their metabolic contributions to enteric methane production. It also identifies the respective critical gaps that need to be filled for aiding the efforts to mitigate methane emission from livestock operations and at the same time increasing the productivity in this critical agriculture sector.

Identification and characterization of archaeal and bacterial F420 -dependent thioredoxin reductases

The thioredoxin pathway is an antioxidant system present in most organisms. Electrons flow from a thioredoxin reductase to thioredoxin at the expense of a specific electron donor. Most known thioredoxin reductases rely on NADPH as a reducing cofactor. Yet, in 2016, a new type of thioredoxin reductase was discovered in Archaea which utilize instead a reduced deazaflavin cofactor (F420 H2 ). For this reason, the respective enzyme was named deazaflavin-dependent flavin-containing thioredoxin reductase (DFTR). To have a broader understanding of the biochemistry of DFTRs, we identified and characterized two other archaeal representatives. A detailed kinetic study, which included pre-steady state kinetic analyses, revealed that these two DFTRs are highly specific for F420 H2 while displaying marginal activity with NADPH. Nevertheless, they share mechanistic features with the canonical thioredoxin reductases that are dependent on NADPH (NTRs). A detailed structural analysis led to the identification of two key residues that tune cofactor specificity of DFTRs. This allowed us to propose a DFTR-specific sequence motif that enabled for the first time the identification and experimental characterization of a bacterial DFTR.

Sepsis, pyruvate, and mitochondria energy supply chain shortage

Balancing high energy-consuming danger resistance and low energy supply of disease tolerance is a universal survival principle that often fails during sepsis. Our research supports the concept that sepsis phosphorylates and deactivates mitochondrial pyruvate dehydrogenase complex control over the tricarboxylic cycle and the electron transport chain. StimulatIng mitochondrial energetics in septic mice and human sepsis cell models can be achieved by inhibiting pyruvate dehydrogenase kinases with the pyruvate structural analog dichloroacetate. Stimulating the pyruvate dehydrogenase complex by dichloroacetate reverses a disruption in the tricarboxylic cycle that induces itaconate, a key mediator of the disease tolerance pathway. Dichloroacetate treatment increases mitochondrial respiration and ATP synthesis, decreases oxidant stress, overcomes metabolic paralysis, regenerates tissue, organ, and innate and adaptive immune cells, and doubles the survival rate in a murine model of sepsis.

Genomic Evidence for the Recycling of Complex Organic Carbon by Novel Thermoplasmatota Clades in Deep-Sea Sediments

Thermoplasmatota have been widely reported in a variety of ecosystems, but their distribution and ecological role in marine sediments are still elusive. Here, we obtained four draft genomes affiliated with the former RBG-16-68-12 clade, which is now considered a new order, “Candidatus Yaplasmales,” of the Thermoplasmatota phylum in sediments from the South China Sea. The phylogenetic trees based on the 16S rRNA genes and draft genomes showed that “Ca. Yaplasmales” archaea are composed of three clades: A, B, and C. Among them, clades A and B are abundantly distributed (up to 10.86%) in the marine anoxic sediment layers (>10-cm depth) of six of eight cores from 1,200- to 3,400-m depths. Metabolic pathway reconstructions indicated that all clades of “Ca. Yaplasmales” have the capacity for alkane degradation by predicted alkyl-succinate synthase. Clade A of “Ca. Yaplasmales” might be mixotrophic microorganisms for the identification of the complete Wood-Ljungdahl pathway and putative genes involved in the degradation of aromatic and halogenated organic compounds. Clades B and C were likely heterotrophic, especially with the potential capacity of the spermidine/putrescine and aromatic compound degradation, as suggested by a significant negative correlation between the concentrations of aromatic compounds and the relative abundances of clade B. The sulfide-quinone oxidoreductase and pyrophosphate-energized membrane proton pump were encoded by all genomes of “Ca. Yaplasmales,” serving as adaptive strategies for energy production. These findings suggest that “Ca. Yaplasmales” might synergistically transform benthic pollutant and detrital organic matter, possibly playing a vital role in the marine and terrestrial sedimentary carbon cycle.

IMPORTANCE Deep oceans receive large amounts of complex organic carbon and anthropogenic pollutants. The deep-sea sediments of the continental slopes serve as the biggest carbon sink on Earth. Particulate organic carbons and detrital proteins accumulate in the sediment. The microbially mediated recycling of complex organic carbon is still largely unknown, which is an important question for carbon budget in global oceans and maintenance of the deep-sea ecosystem. In this study, we report the prevalence (up to 10.86% of the microbial community) of archaea from a novel order of Thermoplasmatota, “Ca. Yaplasmales,” in six of eight cores from 1,200- to 3,400-m depths in the South China Sea. We provide genomic evidence of “Ca. Yaplasmales” in the anaerobic microbial degradation of alkanes, aliphatic and monoaromatic hydrocarbons, and halogenated organic compounds. Our study identifies the key archaeal players in anoxic marine sediments, which are probably critical in recycling the complex organic carbon in global oceans.

Structural Insights into a Fusion Protein between a Glutaredoxin-like and a Ferredoxin-Disulfide Reductase Domain from an Extremophile Bacterium

In eukaryotic photosynthetic organisms, ferredoxin–thioredoxin reductases (FTRs) are key proteins reducing several types of chloroplastic thioredoxins (TRXs) in light conditions. The electron cascade necessary to reduce oxidized TRXs involves a pair of catalytic cysteines and a [4Fe–4S] cluster present at the level of the FTR catalytic subunit, the iron–sulfur cluster receiving electrons from ferredoxins. Genomic analyses revealed the existence of FTR orthologs in non-photosynthetic organisms, including bacteria and archaea, referred to as ferredoxin-disulfide reductase (FDR) as they reduce various types of redoxins. In this study, we describe the tridimensional structure of a natural hybrid protein formed by an N-terminal glutaredoxin-like domain fused to a FDR domain present in the marine bacterium Desulfotalea psychrophila Lsv54. This structure provides information on how and why the absence of the variable subunit present in FTR heterodimer which normally protects the Fe–S cluster is dispensable in FDR proteins. In addition, modelling of a tripartite complex based on the existing structure of a rubredoxin (RBX)–FDR fusion present in anaerobic methanogen archaea allows recapitulating the electron flow involving these RBX, FDR and GRX protein domains.

Structural and Biochemical Characterization of Thioredoxin-2 from Deinococcus radiodurans

Thioredoxin (Trx), a ubiquitous protein showing disulfide reductase activity, plays critical roles in cellular redox control and oxidative stress response. Trx is a member of the Trx system, comprising Trx, Trx reductase (TrxR), and a cognate reductant (generally reduced nicotinamide adenine dinucleotide phosphate, NADPH). Bacterial Trx1 contains only the Trx-fold domain, in which the active site CXXC motif that is critical for the disulfide reduction activity is located. Bacterial Trx2 contains an N-terminal extension, which forms a zinc-finger domain, including two additional CXXC motifs. The multi-stress resistant bacterium Deinococcus radiodurans encodes both Trx1 (DrTrx1) and Trx2 (DrTrx2), which act as members of the enzymatic antioxidant systems. In this study, we constructed Δdrtrx1 and Δdrtrx2 mutants and examined their survival rates under H₂O₂ treated conditions. Both drtrx1 and drtrx2 genes were induced following H₂O₂ treatment, and the Δdrtrx1 and Δdrtrx2 mutants showed a decrease in resistance toward H₂O₂, compared to the wild-type. Native DrTrx1 and DrTrx2 clearly displayed insulin and DTNB reduction activity, whereas mutant DrTrx1 and DrTrx2, which harbors the substitution of conserved cysteine to serine in its active site CXXC motif, showed almost no reduction activity. Mutations in the zinc binding cysteines did not fully eliminate the reduction activities of DrTrx2. Furthermore, we solved the crystal structure of full-length DrTrx2 at 1.96 Å resolution. The N-terminal zinc-finger domain of Trx2 is thought to be involved in Trx-target interaction and, from our DrTrx2 structure, the orientation of the zinc-finger domain of DrTrx2 and its interdomain interaction, between the Trx-fold domain and the zinc-finger domain, is clearly distinguished from those of the other Trx2 structures.

Tat-thioredoxin 1 reduces inflammation by inhibiting pro-inflammatory cytokines and modulating MAPK signaling

Thioredoxin 1 (Trx1) serves a central role in redox homeostasis. It is involved in numerous other processes, including oxidative stress and apoptosis. However, to the best of our knowledge, the role of Trx1 in inflammation remains to be explored. The present study investigated the function and mechanism of cell permeable fused Tat-Trx1 protein in macrophages and a mouse model. Transduction levels of Tat-Trx1 were determined via western blotting. Cellular distribution of transduced Tat-Trx1 was determined by fluorescence microscopy. 2',7'-Dichlorofluorescein diacetate and TUNEL staining were performed to determine the production of reactive oxygen species and DNA fragmentation. Protein and gene expression were measured by western blotting and reverse transcription-quantitative PCR (RT-qPCR), respectively. Effects of skin inflammation were determined using hematoxylin and eosin staining, changes in ear weight and ear thickness, and RT-qPCR in ear edema animal models. Transduced Tat-Trx1 inhibited lipopolysaccharide-induced cytotoxicity and activation of NF-κB, MAPK and Akt. Additionally, Tat-Trx1 markedly reduced the production of inducible nitric oxide synthase, cyclooxygenase-2, IL-1β, IL-6 and TNF-α in macrophages. In a 12-O-tetradecanoylphorbol-13-acetate-induced mouse model, Tat-Trx1 reduced inflammatory damage by inhibiting inflammatory mediator and cytokine production. Collectively, these results demonstrated that Tat-Trx1 could exert anti-inflammatory effects by inhibiting the production of pro-inflammatory mediators and cytokines and by modulating MAPK signaling. Therefore, Tat-Trx1 may be a useful therapeutic agent for diseases induced by inflammatory damage.

On the diversity of F420 -dependent oxidoreductases: A sequence- and structure-based classification

The F₄₂₀ deazaflavin cofactor is an intriguing molecule as it structurally resembles the canonical flavin cofactor, although behaves as a nicotinamide cofactor due to its obligate hydride-transfer reactivity and similar low redox potential. Since its discovery, numerous enzymes relying on it have been described. The known deazaflavoproteins are taxonomically restricted to Archaea and Bacteria. The biochemistry of the deazaflavoenzymes is diverse and they exhibit great structural variability. In this study a thorough sequence and structural homology evolutionary analysis was performed in order to generate an overarching classification of the F₄₂₀ -dependent oxidoreductases. Five different deazaflavoenzyme Classes (I-V) are described according to their structural folds as follows: Class I encompassing the TIM-barrel F₄₂₀ -dependent enzymes; Class II including the Rossmann fold F₄₂₀ -dependent enzymes; Class III comprising the β-roll F₄₂₀ -dependent enzymes; Class IV which exclusively gathers the SH3 barrel F₄₂₀ -dependent enzymes and Class V including the three layer ββα sandwich F₄₂₀ -dependent enzymes. This classification provides a framework for the identification and biochemical characterization of novel deazaflavoenzymes.

Protective Role of Transduced Tat-Thioredoxin1 (Trx1) against Oxidative Stress-Induced Neuronal Cell Death via ASK1-MAPK Signal Pathway

Oxidative stress plays a crucial role in the development of neuronal disorders including brain ischemic injury. Thioredoxin 1 (Trx1), a 12 kDa oxidoreductase, has anti-oxidant and anti-apoptotic functions in various cells. It has been highly implicated in brain ischemic injury. However, the protective mechanism of Trx1 against hippocampal neuronal cell death is not identified yet. Using a cell permeable Tat-Trx1 protein, protective mechanism of Trx1 against hydrogen peroxide-induced cell death was examined using HT-22 cells and an ischemic animal model. Transduced Tat-Trx1 markedly inhibited intracellular ROS levels, DNA fragmentation, and cell death in H₂O₂-treatment HT-22 cells. Tat-Trx1 also significantly inhibited phosphorylation of ASK1 and MAPKs in signaling pathways of HT-22 cells. In addition, Tat-Trx1 regulated expression levels of Akt, NF-κB, and apoptosis related proteins. In an ischemia animal model, Tat-Trx1 markedly protected hippocampal neuronal cell death and reduced astrocytes and microglia activation. These findings indicate that transduced Tat-Trx1 might be a potential therapeutic agent for treating ischemic injury.

Redox and Thiols in Archaea

Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.

Evolution of the thioredoxin system as a step enabling adaptation to oxidative stress

Thioredoxins (Trxs) are low-molecular-weight proteins that participate in the reduction of target enzymes. Trxs contain a redox-active disulfide bond, in the form of a WCGPC amino acid sequence motif, that enables them to perform dithiol-disulfide exchange reactions with oxidized protein substrates. Widely distributed across the three domains of life, Trxs form an evolutionarily conserved family of ancient origin. Thioredoxin reductases (TRs) are enzymes that reduce Trxs. According to their evolutionary history, TRs have diverged, thereby leading to the emergence of variants of the enzyme that in combination with different types of Trxs meet the needs of the cell. In addition to participating in the regulation of metabolism and defense against oxidative stress, Trxs respond to environmental signals-an ability that developed early in evolution. Redox regulation of proteins targeted by Trx is accomplished with a pair of redox-active cysteines located in strategic positions on the polypeptide chain to enable reversible oxidative changes that result in structural and functional modifications target proteins. In this review, we present a general overview of the thioredoxin system and describe recent structural studies on the diversity of its components.

A Genetic System for Methanocaldococcus jannaschii: An Evolutionary Deeply Rooted Hyperthermophilic Methanarchaeon

Phylogenetically deeply rooted methanogens belonging to the genus of Methanocaldococcus living in deep-sea hydrothermal vents derive energy exclusively from hydrogenotrophic methanogenesis, one of the oldest respiratory metabolisms on Earth. These hyperthermophilic, autotrophic archaea synthesize their biomolecules from inorganic substrates and perform high temperature biocatalysis producing methane, a valuable fuel and potent greenhouse gas. The information processing and stress response systems of archaea are highly homologous to those of the eukaryotes. For this broad relevance, Methanocaldococcus jannaschii, the first hyperthermophilic chemolithotrophic organism that was isolated from a deep-sea hydrothermal vent, was also the first archaeon and third organism for which the whole genome sequence was determined. The research that followed uncovered numerous novel information in multiple fields, including those described above. M. jannaschii was found to carry ancient redox control systems, precursors of dissimilatory sulfate reduction enzymes, and a eukaryotic-like protein translocation system. It provided a platform for structural genomics and tools for incorporating unnatural amino acids into proteins. However, the assignments of in vivo relevance to these findings or interrogations of unknown aspects of M. jannaschii through genetic manipulations remained out of reach, as the organism was genetically intractable. This report presents tools and methods that remove this block. It is now possible to knockout or modify a gene in M. jannaschii and genetically fuse a gene with an affinity tag sequence, thereby allowing facile isolation of a protein with M. jannaschii-specific attributes. These tools have helped to genetically validate the role of a novel coenzyme F₄₂₀-dependent sulfite reductase in conferring resistance to sulfite in M. jannaschii and to demonstrate that the organism possesses a deazaflavin-dependent system for neutralizing oxygen.

Comparative Genomics of the Genus Methanohalophilus, Including a Newly Isolated Strain From Kebrit Deep in the Red Sea

Halophilic methanogens play an important role in the carbon cycle in hypersaline environments, but are under-represented in culture collections. In this study, we describe a novel Methanohalophilus strain that was isolated from the sulfide-rich brine-seawater interface of Kebrit Deep in the Red Sea. Based on physiological and phylogenomic features, strain RSK, which is the first methanogenic archaeon to be isolated from a deep hypersaline anoxic brine lake of the Red Sea, represents a novel species of this genus. In order to compare the genetic traits underpinning the adaptations of this genus in diverse hypersaline environments, we sequenced the genome of strain RSK and compared it with genomes of previously isolated and well characterized species in this genus (Methanohalophilus mahii, Methanohalophilus halophilus, Methanohalophilus portucalensis, and Methanohalophilus euhalobius). These analyses revealed a highly conserved genomic core of greater than 93% of annotated genes (1490 genes) containing pathways for methylotrophic methanogenesis, osmoprotection through salt-out strategy, and oxidative stress response, among others. Despite the high degree of genomic conservation, species-specific differences in sulfur and glycogen metabolisms, viral resistance, amino acid, and peptide uptake machineries were also evident. Thus, while Methanohalophilus species are found in diverse extreme environments, each genotype also possesses adaptive traits that are likely relevant in their respective hypersaline habitats.

Response of the Anaerobic Methanotroph "Candidatus Methanoperedens nitroreducens" to Oxygen Stress

"Candidatus Methanoperedens nitroreducens" is an archaeon that couples the anaerobic oxidation of methane to nitrate reduction. In natural and man-made ecosystems, this archaeon is often found at oxic-anoxic interfaces where nitrate, the product of aerobic nitrification, cooccurs with methane produced by methanogens. As such, populations of "Ca Methanoperedens nitroreducens" could be prone to regular oxygen exposure. Here, we investigated the effect of 5% (vol/vol) oxygen exposure in batch activity assays on a "Ca Methanoperedens nitroreducens" culture, enriched from an Italian paddy field. Metagenome sequencing of the DNA extracted from the enrichment culture revealed that 83% of 16S rRNA gene reads were assigned to a novel strain, "Candidatus Methanoperedens nitroreducens Verserenetto." RNA was extracted, and metatranscriptome sequencing upon oxygen exposure revealed that the active community changed, most notably in the appearance of aerobic methanotrophs. The gene expression of "Ca Methanoperedens nitroreducens" revealed that the key genes encoding enzymes of the methane oxidation and nitrate reduction pathways were downregulated. In contrast to this, we identified upregulation of glutaredoxin, thioredoxin family/like proteins, rubrerythrins, peroxiredoxins, peroxidase, alkyl hydroperoxidase, type A flavoproteins, FeS cluster assembly protein, and cysteine desulfurases, indicating the genomic potential of "Ca Methanoperedens nitroreducens Verserenetto" to counteract the oxidative damage and adapt in environments where they might be exposed to regular oxygen intrusion.IMPORTANCE "Candidatus Methanoperedens nitroreducens" is an anaerobic archaeon which couples the reduction of nitrate to the oxidation of methane. This microorganism is present in a wide range of aquatic environments and man-made ecosystems, such as paddy fields and wastewater treatment systems. In such environments, these archaea may experience regular oxygen exposure. However, "Ca Methanoperedens nitroreducens" is able to thrive under such conditions and could be applied for the simultaneous removal of dissolved methane and nitrogenous pollutants in oxygen-limited systems. To understand what machinery "Ca Methanoperedens nitroreducens" possesses to counteract the oxidative stress and survive, we characterized the response to oxygen exposure using a multi-omics approach.

Characterization of TrxC, an Atypical Thioredoxin Exclusively Present in Cyanobacteria

Cyanobacteria form a diverse group of oxygenic photosynthetic prokaryotes considered to be the antecessor of plant chloroplast. They contain four different thioredoxins isoforms, three of them corresponding to m, x and y type present in plant chloroplast, while the fourth one (named TrxC) is exclusively found in cyanobacteria. TrxC has a modified active site (WCGLC) instead of the canonical (WCGPC) present in most thioredoxins. We have purified it and assayed its activity but surprisingly TrxC lacked all the classical activities, such as insulin precipitation or activation of the fructose-1,6-bisphosphatase. Mutants lacking trxC or over-expressing it were generated in the model cyanobacterium Synechocystis sp. PCC 6803 and their phenotypes have been analyzed. The ΔtrxC mutant grew at similar rates to WT in all conditions tested although it showed an increased carotenoid content especially under low carbon conditions. Overexpression strains showed reduced growth under the same conditions and accumulated lower amounts of carotenoids. They also showed lower oxygen evolution rates at high light but higher Fv’/Fm’ and Non-photochemical-quenching (NPQ) in dark adapted cells, suggesting a more oxidized plastoquinone pool. All these data suggest that TrxC might have a role in regulating photosynthetic adaptation to low carbon and/or high light conditions.

Toward a mechanistic and physiological understanding of a ferredoxin:disulfide reductase from the domains Archaea and Bacteria

Disulfide reductases reduce other proteins and are critically important for cellular redox signaling and homeostasis. Methanosarcina acetivorans is a methane-producing microbe from the domain Archaea that produces a ferredoxin:disulfide reductase (FDR) for which the crystal structure has been reported, yet its biochemical mechanism and physiological substrates are unknown. FDR and the extensively characterized plant-type ferredoxin:thioredoxin reductase (FTR) belong to a distinct class of disulfide reductases that contain a unique active-site [4Fe-4S] cluster. The results reported here support a mechanism for FDR similar to that reported for FTR with notable exceptions. Unlike FTR, FDR contains a rubredoxin [1Fe-0S] center postulated to mediate electron transfer from ferredoxin to the active-site [4Fe-4S] cluster. UV-visible, EPR, and Mössbauer spectroscopic data indicated that two-electron reduction of the active-site disulfide in FDR involves a one-electron-reduced [4Fe-4S]¹⁺ intermediate previously hypothesized for FTR. Our results support a role for an active-site tyrosine in FDR that occupies the equivalent position of an essential histidine in the active site of FTR. Of note, one of seven Trxs encoded in the genome (Trx5) and methanoredoxin, a glutaredoxin-like enzyme from M. acetivorans, were reduced by FDR, advancing the physiological understanding of FDR's role in the redox metabolism of methanoarchaea. Finally, bioinformatics analyses show that FDR homologs are widespread in diverse microbes from the domain Bacteria.

Metabolic shift at the class level sheds light on adaptation of methanogens to oxidative environments

Methanogens have long been considered strictly anaerobic and oxygen-sensitive microorganisms, but their ability to survive oxygen stress has also been documented. Indeed, methanogens have been found in oxidative environments, and antioxidant genes have been detected in their genomes. How methanogens adapt to oxidative environments, however, remain poorly understood. Here, we systematically predicted and annotated antioxidant features from representative genomes across six well-established methanogen orders. Based on functional gene content involved in production of reactive oxygen species, Hierarchical Clustering analyses grouped methanogens into two distinct clusters, corresponding to the Class I and II methanogens, respectively. Comparative genomics suggested a systematic shift in metabolisms across the two classes, resulting in an enrichment of antioxidant features in the Class II. Moreover, meta-analysis of 16 S rRNA gene sequences obtained from EnvDB indicated that members of Class II were more frequently recovered from microaerophilic and even oxic environments than the Class I members. Phylogenomic analysis suggested that the Class I and II methanogens might have evolved before and around the Great Oxygenation Event, respectively. The enrichment of antioxidant features in the Class II methanogens may have played a key role in the adaption of this group to oxidative environments today and historically.

Biochemical Function, Molecular Structure and Evolution of an Atypical Thioredoxin Reductase from Desulfovibrio vulgaris

Thioredoxin reductase (TR) regulates the intracellular redox environment by reducing thioredoxin (Trx). In anaerobes, recent findings indicate that the Trx redox network is implicated in the global redox regulation of metabolism but also actively participates in protecting cells against O₂. In the anaerobe Desulfovibrio vulgaris Hildenborough (DvH), there is an intriguing redundancy of the Trx system which includes a classical system using NADPH as electron source, a non-canonical system using NADH and an isolated TR (DvTRi). The functionality of DvTRi was questioned due to its lack of reactivity with DvTrxs. Structural analysis shows that DvTRi is a NAD(P)H-independent TR but its reducer needs still to be identified. Moreover, DvTRi reduced by an artificial electron source is able to reduce in turn DvTrx1 and complexation experiments demonstrate a direct interaction between DvTRi and DvTrx1. The deletion mutant tri exhibits a higher sensitivity to disulfide stress and the gene tri is upregulated by O₂ exposure. Having DvTRi in addition to DvTR1 as electron source for reducing DvTrx1 must be an asset to combat oxidative stress. Large-scale phylogenomics analyses show that TRi homologs are confined within the anaerobes. All TRi proteins displayed a conserved TQ/NGK motif instead of the HRRD motif, which is selective for the binding of the 2′-phosphate group of NADPH. The evolutionary history of TRs indicates that tr1 is the common gene ancestor in prokaryotes, affected by both gene duplications and horizontal gene events, therefore leading to the appearance of TRi through subfunctionalization over the evolutionary time.

A Reexamination of Thioredoxin Reductase from Thermoplasma acidophilum, a Thermoacidophilic Euryarchaeon, Identifies It as an NADH-Dependent Enzyme

Flavin-containing Trx reductase (TrxR) of Thermoplasma acidophilum (Ta), a thermoacidophilic facultative anaerobic archaeon, lacks the structural features for the binding of 2'-phosphate of nicotinamide adenine dinucleotide phosphate (NADPH), and this feature has justified the observed lack of activity with NADPH; NADH has also been reported to be ineffective. Our recent phylogenetic analysis identified Ta-TrxR as closely related to the NADH-dependent enzymes of Thermotoga maritima and Desulfovibrio vulgaris, both being anaerobic bacteria. This observation instigated a reexamination of the activity of the enzyme, which showed that Ta-TrxR is NADH dependent; the apparent K_m for NADH was 3.1 μM, a physiologically relevant value. This finding is consistent with the observation that NADH:TrxR has thus far been found primarily in anaerobic bacteria and archaea.

The Deep Thioredoxome in Chlamydomonas reinhardtii: New Insights into Redox Regulation

Thiol-based redox post-translational modifications have emerged as important mechanisms of signaling and regulation in all organisms, and thioredoxin plays a key role by controlling the thiol-disulfide status of target proteins. Recent redox proteomic studies revealed hundreds of proteins regulated by glutathionylation and nitrosylation in the unicellular green alga Chlamydomonas reinhardtii, while much less is known about the thioredoxin interactome in this organism. By combining qualitative and quantitative proteomic analyses, we have comprehensively investigated the Chlamydomonas thioredoxome and 1188 targets have been identified. They participate in a wide range of metabolic pathways and cellular processes. This study broadens not only the redox regulation to new enzymes involved in well-known thioredoxin-regulated metabolic pathways but also sheds light on cellular processes for which data supporting redox regulation are scarce (aromatic amino acid biosynthesis, nuclear transport, etc). Moreover, we characterized 1052 thioredoxin-dependent regulatory sites and showed that these data constitute a valuable resource for future functional studies in Chlamydomonas. By comparing this thioredoxome with proteomic data for glutathionylation and nitrosylation at the protein and cysteine levels, this work confirms the existence of a complex redox regulation network in Chlamydomonas and provides evidence of a tremendous selectivity of redox post-translational modifications for specific cysteine residues.

Thioredoxin promotes survival signaling events under nitrosative/oxidative stress associated with cancer development

Accumulating mutations may drive cells into the acquisition of abnormal phenotypes that are characteristic of cancer cells. Cancer cells feature profound alterations in proliferation programs that result in a new population of cells that overrides normal tissue construction and maintenance programs. To achieve this goal, cancer cells are endowed with up regulated survival signaling pathways. They also must counteract the cytotoxic effects of high levels of nitric oxide (NO) and of reactive oxygen species (ROS), which are by products of cancer cell growth. Accumulating experimental evidence associates cancer cell survival with their capacity to up-regulate antioxidant systems. Elevated expression of the antioxidant protein thioredoxin-1 (Trx1) has been correlated with cancer development. Trx1 has been characterized as a multifunctional protein, playing different roles in different cell compartments. Trx1 migrates to the nucleus in cells exposed to nitrosative/oxidative stress conditions. Trx1 nuclear migration has been related to the activation of transcription factors associated with cell survival and cell proliferation. There is a direct association between the p21Ras-ERK1/2 MAP Kinases survival signaling pathway and Trx1 nuclear migration under nitrosative stress. The expression of the cytoplasmic protein, the thioredoxin-interacting protein (Txnip), determines the change in Trx1 cellular compartmentalization. The anti-apoptotic actions of Trx1 and its denitrosylase activity occur in the cytoplasm and serve as important regulators of cell survival. Within this context, this review focuses on the participation of Trx1 in cells under nitrosative/oxidative stress in survival signaling pathways associated with cancer development.

Expansion of the redox-sensitive proteome coincides with the plastid endosymbiosis

The redox-sensitive proteome (RSP) consists of protein thiols that undergo redox reactions, playing an important role in coordinating cellular processes. Here, we applied a large-scale phylogenomic reconstruction approach in the model diatom Phaeodactylum tricornutum to map the evolutionary origins of the eukaryotic RSP. The majority of P. tricornutum redox-sensitive cysteines (76%) is specific to eukaryotes, yet these are encoded in genes that are mostly of a prokaryotic origin (57%). Furthermore, we find a threefold enrichment in redox-sensitive cysteines in genes that were gained by endosymbiotic gene transfer during the primary plastid acquisition. The secondary endosymbiosis event coincides with frequent introduction of reactive cysteines into existing proteins. While the plastid acquisition imposed an increase in the production of reactive oxygen species, our results suggest that it was accompanied by significant expansion of the RSP, providing redox regulatory networks the ability to cope with fluctuating environmental conditions.

Redox regulation of SurR by protein disulfide oxidoreductase in Thermococcus onnurineus NA1

Protein disulfide oxidoreductases are redox enzymes that catalyze thiol-disulfide exchange reactions. These enzymes include thioredoxins, glutaredoxins, protein disulfide isomerases, disulfide bond formation A (DsbA) proteins, and Pyrococcus furiosus protein disulfide oxidoreductase (PfPDO) homologues. In the genome of a hyperthermophilic archaeon, Thermococcus onnurineus NA1, the genes encoding one PfPDO homologue (TON_0319, Pdo) and three more thioredoxin- or glutaredoxin-like proteins (TON_0470, TON_0472, TON_0834) were identified. All except TON_0470 were recombinantly expressed and purified. Three purified proteins were reduced by a thioredoxin reductase (TrxR), indicating that each protein can form redox complex with TrxR. SurR, a transcription factor involved in the sulfur response, was tested for a protein target of a TrxR-redoxin system and only Pdo was identified to be capable of catalyzing the reduction of SurR. Electromobility shift assay demonstrated that SurR reduced by the TrxR-Pdo system could bind to the DNA probe with the SurR-binding motif, GTTttgAAC. In this study, we present the TrxR-Pdo couple as a redox-regulator for SurR in T. onnurineus NA1.

Methanosarcina acetivorans utilizes a single NADPH-dependent thioredoxin system and contains additional thioredoxin homologues with distinct functions

The thioredoxin system plays a central role in the intracellular redox maintenance in the majority of cells. The canonical system consists of an NADPH-dependent thioredoxin reductase (TrxR) and thioredoxin (Trx), a disulfide reductase. Although Trx is encoded in almost all sequenced genomes of methanogens, its incorporation into their unique physiology is not well understood. Methanosarcina acetivorans contains a single TrxR (MaTrxR) and seven Trx (MaTrx1-MaTrx7) homologues. We previously showed that MaTrxR and at least MaTrx7 compose a functional NADPH-dependent thioredoxin system. Here, we report the characterization of all seven recombinant MaTrxs. MaTrx1, MaTrx3, MaTrx4 and MaTrx5 lack appreciable disulfide reductase activity, unlike previously characterized MaTrx2, MaTrx6 and MaTrx7. Enzyme assays demonstrated that, of the MaTrxs, only the reduction of disulfide-containing MaTrx7 is linked to the oxidation of reduced coenzymes. NADPH is shown to be supplied to the MaTrxR-MaTrx7 system through the oxidation of the primary methanogen electron carriers F420H2 and ferredoxin, indicating that it serves as a primary intracellular reducing system in M. acetivorans. Bioinformatic analyses also indicate that the majority of methanogens likely utilize an NADPH-dependent thioredoxin system. The remaining MaTrxs may have specialized functions. MaTrx1 and MaTrx3 exhibited thiol oxidase activity. MaTrx3 and MaTrx6 are targeted to the membrane of M. acetivorans and likely function in the formation and the reduction of disulfides in membrane and/or extracellular proteins, respectively. This work provides insight into the incorporation of Trx into the metabolism of methanogens, and this reveals that methanogens contain Trx homologues with alternative properties and activities.

Dithiol disulphide exchange in redox regulation of chloroplast enzymes in response to evolutionary and structural constraints

Redox regulation of chloroplast enzymes via disulphide reduction is believed to control the rates of CO₂ fixation. The study of the thioredoxin reduction pathways and of various target enzymes lead to the following guidelines.

A Novel F420-dependent Thioredoxin Reductase Gated by Low Potential FAD: A TOOL FOR REDOX REGULATION IN AN ANAEROBE

A recent report suggested that the thioredoxin-dependent metabolic regulation, which is widespread in all domains of life, existed in methanogenic archaea about 3.5 billion years ago. We now show that the respective electron delivery enzyme (thioredoxin reductase, TrxR), although structurally similar to flavin-containing NADPH-dependent TrxRs (NTR), lacked an NADPH-binding site and was dependent on reduced coenzyme F₄₂₀ (F₄₂₀H₂), a stronger reductant with a mid-point redox potential (E'₀) of -360 mV; E'₀ of NAD(P)H is -320 mV. Because F₄₂₀ is a deazaflavin, this enzyme was named deazaflavin-dependent flavin-containing thioredoxin reductase (DFTR). It transferred electrons from F₄₂₀H₂ to thioredoxin via protein-bound flavin; K_m values for thioredoxin and F₄₂₀H₂ were 6.3 and 28.6 μm, respectively. The E'₀ of DFTR-bound flavin was approximately -389 mV, making electron transfer from NAD(P)H or F₄₂₀H₂ to flavin endergonic. However, under high partial pressures of hydrogen prevailing on early Earth and present day deep-sea volcanoes, the potential for the F₄₂₀/F₄₂₀H₂ pair could be as low as -425 mV, making DFTR efficient. The presence of DFTR exclusively in ancient methanogens and mostly in the early Earth environment of deep-sea volcanoes and DFTR's characteristics suggest that the enzyme developed on early Earth and gave rise to NTR. A phylogenetic analysis revealed six more novel-type TrxR groups and suggested that the broader flavin-containing disulfide oxidoreductase family is more diverse than previously considered. The unprecedented structural similarities between an F₄₂₀-dependent enzyme (DFTR) and an NADPH-dependent enzyme (NTR) brought new thoughts to investigations on F₄₂₀ systems involved in microbial pathogenesis and antibiotic production.

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

5-Deazaflavin cofactors enhance the metabolic flexibility of microorganisms by catalyzing a wide range of challenging enzymatic redox reactions. While structurally similar to riboflavin, 5-deazaflavins have distinctive and biologically useful electrochemical and photochemical properties as a result of the substitution of N-5 of the isoalloxazine ring for a carbon. 8-Hydroxy-5-deazaflavin (Fo) appears to be used for a single function: as a light-harvesting chromophore for DNA photolyases across the three domains of life. In contrast, its oligoglutamyl derivative F420 is a taxonomically restricted but functionally versatile cofactor that facilitates many low-potential two-electron redox reactions. It serves as an essential catabolic cofactor in methanogenic, sulfate-reducing, and likely methanotrophic archaea. It also transforms a wide range of exogenous substrates and endogenous metabolites in aerobic actinobacteria, for example mycobacteria and streptomycetes. In this review, we discuss the physiological roles of F420 in microorganisms and the biochemistry of the various oxidoreductases that mediate these roles. Particular focus is placed on the central roles of F420 in methanogenic archaea in processes such as substrate oxidation, C1 pathways, respiration, and oxygen detoxification. We also describe how two F420-dependent oxidoreductase superfamilies mediate many environmentally and medically important reactions in bacteria, including biosynthesis of tetracycline and pyrrolobenzodiazepine antibiotics by streptomycetes, activation of the prodrugs pretomanid and delamanid by Mycobacterium tuberculosis, and degradation of environmental contaminants such as picrate, aflatoxin, and malachite green. The biosynthesis pathways of Fo and F420 are also detailed. We conclude by considering opportunities to exploit deazaflavin-dependent processes in tuberculosis treatment, methane mitigation, bioremediation, and industrial biocatalysis.

Comprehensively Characterizing the Thioredoxin Interactome In Vivo Highlights the Central Role Played by This Ubiquitous Oxidoreductase in Redox Control

Thioredoxin (Trx) is a ubiquitous oxidoreductase maintaining protein-bound cysteine residues in the reduced thiol state. Here, we combined a well-established method to trap Trx substrates with the power of bacterial genetics to comprehensively characterize the in vivo Trx redox interactome in the model bacterium Escherichia coli Using strains engineered to optimize trapping, we report the identification of a total 268 Trx substrates, including 201 that had never been reported to depend on Trx for reduction. The newly identified Trx substrates are involved in a variety of cellular processes, ranging from energy metabolism to amino acid synthesis and transcription. The interaction between Trx and two of its newly identified substrates, a protein required for the import of most carbohydrates, PtsI, and the bacterial actin homolog MreB was studied in detail. We provide direct evidence that PtsI and MreB contain cysteine residues that are susceptible to oxidation and that participate in the formation of an intermolecular disulfide with Trx. By considerably expanding the number of Trx targets, our work highlights the role played by this major oxidoreductase in a variety of cellular processes. Moreover, as the dependence on Trx for reduction is often conserved across species, it also provides insightful information on the interactome of Trx in organisms other than E. coli.

How did life survive Earth's great oxygenation?

Life on Earth originated and evolved in anoxic environments. Around 2.4 billion-years-ago, ancestors of Cyanobacteria invented oxygenic photosynthesis, producing substantial amounts of O2 as a byproduct of phototrophic water oxidation. The sudden appearance of O2 would have led to significant oxidative stress due to incompatibilities with core cellular biochemical processes. Here we examine this problem through the lens of Cyanobacteria-the first taxa to observe significant fluxes of intracellular dioxygen. These early oxygenic organisms likely adapted to the oxidative stress by co-opting preexisting systems (exaptation) with fortuitous antioxidant properties. Over time more advanced antioxidant systems evolved, allowing Cyanobacteria to adapt to an aerobic lifestyle and become the most important environmental engineers in Earth history.

Structural and Biochemical Characterizations of Methanoredoxin from Methanosarcina acetivorans, a Glutaredoxin-Like Enzyme with Coenzyme M-Dependent Protein Disulfide Reductase Activity

Glutaredoxins (GRXs) are thiol-disulfide oxidoreductases abundant in prokaryotes, although little is understood of these enzymes from the domain Archaea. The numerous characterized GRXs from the domain Bacteria utilize a diversity of low-molecular-weight thiols in addition to glutathione as reductants. We report here the biochemical and structural properties of a GRX-like protein named methanoredoxin (MRX) from Methanosarcina acetivorans of the domain Archaea. MRX utilizes coenzyme M (CoMSH) as reductant for insulin disulfide reductase activity, which adds to the diversity of thiol protectants in prokaryotes. Cell-free extracts of M. acetivorans displayed CoMS-SCoM reductase activity that complements the CoMSH-dependent activity of MRX. The crystal structure exhibits a classic thioredoxin-glutaredoxin fold comprising three α-helices surrounding four antiparallel β-sheets. A pocket on the surface contains a CVWC motif, identifying the active site with architecture similar to GRXs. Although it is a monomer in solution, the crystal lattice has four monomers in a dimer of dimers arrangement. A cadmium ion is found within the active site of each monomer. Two such ions stabilize the N-terminal tails and dimer interfaces. Our modeling studies indicate that CoMSH and glutathione (GSH) bind to the active site of MRX similar to the binding of GSH in GRXs, although there are differences in the amino acid composition of the binding motifs. The results, combined with our bioinformatic analyses, show that MRX represents a class of GRX-like enzymes present in a diversity of methane-producing Archaea.

Structural and Biochemical Characterization of a Ferredoxin:Thioredoxin Reductase-like Enzyme from Methanosarcina acetivorans

Bioinformatics analyses predict the distribution in nature of several classes of diverse disulfide reductases that evolved from an ancestral plant-type ferredoxin:thioredoxin reductase (FTR) catalytic subunit to meet a variety of ecological needs. Methanosarcina acetivorans is a methane-producing species from the domain Archaea predicted to encode an FTR-like enzyme with two domains, one resembling the FTR catalytic subunit and the other containing a rubredoxin-like domain replacing the variable subunit of present-day FTR enzymes. M. acetivorans is of special interest as it was recently proposed to have evolved at the time of the end-Permian extinction and to be largely responsible for the most severe biotic crisis in the fossil record by converting acetate to methane. The crystal structure and biochemical characteristics were determined for the FTR-like enzyme from M. acetivorans, here named FDR (ferredoxin disulfide reductase). The results support a role for the rubredoxin-like center of FDR in transfer of electrons from ferredoxin to the active-site [Fe₄S₄] cluster adjacent to a pair of redox-active cysteines participating in reduction of disulfide substrates. A mechanism is proposed for disulfide reduction similar to one of two mechanisms previously proposed for the plant-type FTR. Overall, the results advance the biochemical and evolutionary understanding of the FTR-like family of enzymes and the conversion of acetate to methane that is an essential link in the global carbon cycle and presently accounts for most of this greenhouse gas that is biologically generated.

Acceleration of protein folding by four orders of magnitude through a single amino acid substitution

Cis prolyl peptide bonds are conserved structural elements in numerous protein families, although their formation is energetically unfavorable, intrinsically slow and often rate-limiting for folding. Here we investigate the reasons underlying the conservation of the cis proline that is diagnostic for the fold of thioredoxin-like thiol-disulfide oxidoreductases. We show that replacement of the conserved cis proline in thioredoxin by alanine can accelerate spontaneous folding to the native, thermodynamically most stable state by more than four orders of magnitude. However, the resulting trans alanine bond leads to small structural rearrangements around the active site that impair the function of thioredoxin as catalyst of electron transfer reactions by more than 100-fold. Our data provide evidence for the absence of a strong evolutionary pressure to achieve intrinsically fast folding rates, which is most likely a consequence of proline isomerases and molecular chaperones that guarantee high in vivo folding rates and yields.

Comparative genomics of three Methanocellales strains reveal novel taxonomic and metabolic features

Methanocellales represents a new order of methanogens, which is widespread in environments and plays specifically the important role in methane emissions from paddy fields. To gain more insights into Methanocellales, comparative genomic studies were performed among three Methanocellales strains through the same annotation pipeline. Genetic relationships among strains revealed by genome alignment, pan-genome reconstruction and comparison of amino average identity suggest that they should be classified in different genera. In addition, multiple copies of cell cycle regulator proteins were identified for the first time in Archaea. Core metabolisms were reconstructed, predicting certain unique and novel features for Methanocellales, including a set of methanogenesis genes potentially organized toward specialization in utilizing low concentrations of H2, a new route of disulfide reduction catalysed by a disulfide-reducing hydrogenase (Drh) complex phylogenetically related to sulfate-reducing prokaryotes, an oxidative tricarboxylic acid (TCA) cycle, a sophisticated nitrogen uptake and regulation system as well as a versatile sulfur utilization system. These core metabolisms are largely conserved among the three strains, but differences in gene copy number and metabolic diversity are evident. The present study thus adds new dimensions to the unique ecophysiology of Methanocellales and offers a road map for further experimental characterization of this methanogen lineage.

The Methanosarcina acetivorans thioredoxin system activates DNA binding of the redox-sensitive transcriptional regulator MsvR

The production of biogas (methane) by an anaerobic digestion is an important facet to renewable energy, but is subject to instability due to the sensitivity of strictly anaerobic methanogenic archaea (methanogens) to environmental perturbations, such as oxygen. An understanding of the oxidant-sensing mechanisms used by methanogens may lead to the development of more oxidant tolerant (i.e., stable) methanogen strains. MsvR is a redox-sensitive transcriptional regulator that is found exclusively in methanogens. We show here that oxidation of MsvR from Methanosarcina acetivorans (MaMsvR) with hydrogen peroxide oxidizes cysteine thiols, which inactivates MaMsvR binding to its own promoter (P(msvR)). Incubation of oxidized MaMsvR with the M. acetivorans thioredoxin system (NADPH, MaTrxR, and MaTrx7) results in reduction of the cysteines back to thiols and activation of P msvR binding. These data confirm that cysteines are critical for the thiol-disulfide regulation of P(msvR) binding by MaMsvR and support a role for the M. acetivorans thioredoxin system in the in vivo activation of MaMsvR. The results support the feasibility of using MaMsvR and P(msvR), along with the Methanosarcina genetic system, to design methanogen strains with oxidant-regulated gene expression systems, which may aid in stabilizing anaerobic digestion.

Molecular characterization of the thioredoxin system from Methanosarcina acetivorans

The thioredoxin system, composed of thioredoxin reductase (TrxR) and thioredoxin (Trx), is widely distributed in nature, where it serves key roles in electron transfer and in the defense against oxidative stress. Although recent evidence reveals Trx homologues are almost universally present among the methane-producing archaea (methanogens), a complete thioredoxin system has not been characterized from any methanogen. We examined the phylogeny of Trx homologues among methanogens and characterized the thioredoxin system from Methanosarcina acetivorans. Phylogenetic analysis of Trx homologues from methanogens revealed eight clades, with one clade containing Trxs broadly distributed among methanogens. The Methanococci and Methanobacteria each contain one additional Trx from another clade, respectively, whereas the Methanomicrobia contain an additional five distinct Trxs. Methanosarcina acetivorans, a member of the Methanomicrobia, contains a single TrxR (MaTrxR) and seven Trx homologues (MaTrx1-7), with representatives from five of the methanogen Trx clades. Purified recombinant MaTrxR had 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) reductase and oxidase activities. The apparent Km value for NADPH was 115-fold lower than that for NADH, consistent with NADPH as the physiological electron donor to MaTrxR. Purified recombinant MaTrx2, MaTrx6 and MaTrx7 exhibited dithiothreitol- and lipoamide-dependent insulin disulfide reductase activities. However, only MaTrx7, which is encoded adjacent to MaTrxR, could serve as a redox partner to MaTrxR. These results reveal that M. acetivorans harbors at least three functional and distinct Trxs, and a complete thioredoxin system composed of NADPH, MaTrxR and at least MaTrx7. This is the first characterization of a complete thioredoxin system from a methanogen, which provides a foundation to understand the system in methanogens.