A thermostable bacterial catalase-peroxidase oxidizes phenolic compounds derived from lignins.

Lignocellulosic biomass is rich in lignins, which represent a bottomless natural source of aromatic compounds. Due to the high chemical complexity of these aromatic polymers, their biological fractionation remains challenging for biorefinery. The production of aromatics from the biological valorization of lignins requires the action of ligninolytic peroxidases and laccases produced by fungi and bacteria. Therefore, identification of efficient ligninolytic enzymes with high stability represents a promising route for lignins biorefining. Our strategy consists in exploiting the enzymatic potential of the thermophilic bacterium Thermobacillus xylanilyticus to produce robust and thermostable ligninolytic enzymes. In this context, a gene encoding a putative catalase-peroxidase was identified from the bacterial genome. The present work describes the production of the recombinant protein, its biochemical characterization, and ligninolytic potential. Our results show that the catalase-peroxidase from T. xylanilyticus is thermostable and exhibits catalase-peroxidase and manganese peroxidase activities. The electrochemical characterization using intermittent pulse amperometry showed the ability of the enzyme to oxidize small aromatic compounds derived from lignins. This promising methodology allows the fast screening of the catalase-peroxidase activity towards small phenolic molecules, suggesting its potential role in lignin transformation. KEY POINTS: • Production and characterization of a new thermostable bacterial catalase-peroxidase • The enzyme is able to oxidize many phenolic monomers derived from lignins • Intermittent pulse amperometry is promising to screen ligninolytic enzyme.

Structural and physical-chemical characterization of redox active CeO2nanoparticles synthesized by precipitation in water-alcohol solutions.

A set of cerium dioxide nanoparticles (CeO2NPs) was synthesized by precipitation in water-alcohol solutions under conditions when the physical-chemical parameters of synthesized NPs were controlled by changing the ratio of the reaction components. The size of CeO2NPs is controlled largely by the dielectric constant of the reaction solution. An increase of the percentage of Ce3+ions at the surface was observed with a concomitant reduction of the NP sizes. All synthesized CeO2NPs possess relatively high positive values of zeta-potential (ζ > 40 mV) suggesting good stability in aqueous suspensions. Analysis of the valence- and size-dependent rate of hydrogen peroxide decomposition revealed that catalase/peroxidase-like activity of CeO2NPs is higher at a low percentage of Ce3+at the NP surface. In contrast, smaller CeO2NPs with a higher percentage of Ce3+at the NP surface display a higher oxidase-like activity.

Structural basis for isoniazid resistance in KatG double mutants of Mycobacterium tuberculosis.

The failure of drugs for effective treatment against infectious diseases can be attributed to resistant forms of causative agents. The evasive nature of Mycobacterium tuberculosis is partly associated to its physical features, such as having a thick cell wall and incorporation of beneficial mutations leading to drug resistance. The pro drug Isoniazid (INH) interacts with an enzyme catalase peroxidase to get converted into its active form and upon activation stops the cell wall synthesis thus killing the Mycobacterium. The most common mutation i.e. S315T leads to high degree of drug resistance by virtue of its position in the active site. Here, we have characterized the prominent attributes of two double mutant isolates S315 T/D194G and S315T/M624V which are multi drug resistant and extremely drug resistant, respectively. Protein models were generated using the crystal structure which were then subjected to energy minimization and long term molecular dynamics simulations. Further, computational analysis showed decreasing ability of INH binding to the mutants in order of: Native > S315T/D194G > S315T/M624V. Also, a trend was observed that as the docking score and binding area decreased, there was a significant increase in the distortion of the 3D geometry of the mutants as observed by PCA analysis.

Structure, kinetics, molecular and redox properties of a cytosolic and developmentally regulated fungal catalase-peroxidase.

CAT-2, a cytosolic catalase-peroxidase (CP) from Neurospora crassa, which is induced during asexual spore formation, was heterologously expressed and characterized. CAT-2 had the Met-Tyr-Trp (M-Y-W) adduct required for catalase activity. Its KM for H2O2 was micromolar for peroxidase and millimolar for catalase activity. A Em = -158 mV reduction potential value was obtained and the Soret band shift suggested a mixture of low and high spin ferric iron. CAT-2 EPR spectrum at 10 K indicated an axial and a rhombic component. With peroxyacetic acid (PAA), formation of Compound I* was observed with EPR. CAT-2 homodimer crystallographic structure contained two K+ ions; Glu107 residues were displaced to bind them. CAT-2 showed the essential amino acid residues for activity in similar positions to other CPs. CAT-2 Arg426 is oriented towards the M-Y-W adduct, interacting with the deprotonated Tyr238 hydroxyl group. A perhydroxy modification of the indole nitrogen of Trp90 was oriented toward the catalytic His91. In contrast to cytochrome c peroxidase and ascorbate peroxidase, the catalase-peroxidase heme propionates are not exposed to the solvent. Together with other N. crassa enzymes that utilize H2O2 as a substrate, CAT-2 has many tryptophan and proline residues at its surface, probably related to H2O2 selection in water.

The roles of peroxide protective regulons in protecting Xanthomonas campestris pv. campestris from sodium hypochlorite stress.

The exposure of Xanthomonas campestris pv. campestris to sublethal concentrations of a sodium hypochlorite (NaOCl) solution induced the expression of genes that encode peroxide scavenging enzymes within the OxyR and OhrR regulons. Sensitivity testing in various X. campestris mutants indicated that oxyR, katA, katG, ahpC, and ohr contributed to protection against NaOCl killing. The pretreatment of X. campestris cultures with oxidants, such as hydrogen peroxide (H2O2), t-butyl hydroperoxide, and the superoxide generator menadione, protected the bacteria from lethal concentrations of NaOCl in an OxyR-dependent manner. Treating the bacteria with a low concentration of NaOCl resulted in the adaptive protection from NaOCl killing and also provided cross-protection from H2O2 killing. Taken together, the results suggest that the toxicity of NaOCl is partially mediated by the generation of peroxides and other reactive oxygen species that are removed by primary peroxide scavenging enzymes, such as catalases and AhpC, as a part of an overall strategy that protects the bacteria from the lethal effects of NaOCl.

Paper-based electrodes as a tool for detecting ligninolytic enzymatic activities.

Lignin is the most important natural source of aromatic compounds. The valorisation of lignin into aromatics requires fractionation steps that can be catalysed by ligninolytic enzymes. However, one of the main limitations of biological lignin fractionation is the low efficiency of biocatalysts; it is therefore crucial to enhance or to identify new ligninolytic enzymes. Currently, the screening of ligninolytic activities on lignin polymers represents a technological bottenleck and hinders the characterization and the discovery of efficient ligninolytic biocatalysts. An efficient and fast method for the measurement of such enzymatic activities is therefore required. In this work, we present a new electrochemical tool based on lignin-coated paper electrodes for the detection and the characterization of ligninolytic activity. The suitability of this method is demonstrated using a catalase-peroxidase isolated from Thermobacillus xylanilyticus.

Characterization of a catalase-peroxidase variant (L333V-KatG) identified in an INH-resistant Mycobacterium tuberculosis clinical isolate.

Mycobacterium tuberculosis catalase-peroxidase (Mt-KatG) is a bifunctional heme-dependent enzyme that has been shown to activate isoniazid (INH), the widely used antibiotic against tuberculosis (TB). The L333V-KatG variant has been associated with INH resistance in clinical M. tuberculosis isolates from Mexico. To understand better the mechanisms of INH activation, its catalytic properties (catalase, peroxidase, and IN-NAD formation) and crystal structure were compared with those of the wild-type enzyme (WT-KatG). The rate of IN-NAD formation mediated by WT-KatG was 23% greater than L333V-KatG when INH concentration is varied. In contrast to WT-KatG, the crystal structure of the L333V-KatG variant has a perhydroxy modification of the indole nitrogen of W107 from MYW adduct. L333V-KatG shows most of the active site residues in a similar position to WT-KatG; only R418 is in the R-conformation instead of the double R and Y conformation present in WT-KatG. L333V-KatG shows a small displacement respect to WT-KatG in the helix from R385 to L404 towards the mutation site, an increase in length of the coordination bond between H270 and heme Fe, and a longer H-bond between proximal D381 and W321, compared to WT-KatG; these small displacements could explain the altered redox potential of the heme, and result in a less active and stable enzyme.

Cu-promoted synthesis of triclosan-Mannich and Glaser adducts: anti-mycobacterial evaluation with in silico validations.

Aim: The WHO, Global tuberculosis report 2022 estimated number of tuberculosis (TB) cases reached 10.6 million in 2021, reflecting a 4.5% increase compared with the 10.1 million reported in 2020. The incidence rate of TB showed 3.6% rise from 2020 to 2021. Results/methodology: This manuscript discloses Cu-promoted single pot A3-coupling between triclosan (TCS)-based alkyne, formaldehyde and secondary amines to yield TCS-based Mannich adducts. Additionally, the coupling of TCS-alkynes in the presence of Cu(OAc)2 afforded the corresponding homodimers. Among tested compounds, the most potent one in the series 11 exhibited fourfold higher potency than rifabutin against drug-resistant Mycobacterium abscessus. The selectivity index was also substantially improved, being 26 (day 1) and 15 (day 3), which is four-times better than TCS.

[Box: see text].

Functional characterization of extracellular and intracellular catalase-peroxidases involved in virulence of the fungal wheat pathogen Zymoseptoria tritici.

Understanding how pathogens defend themselves against host defence mechanisms, such as hydrogen peroxide (H2O2) production, is crucial for comprehending fungal infections. H2O2 poses a significant threat to invading fungi due to its potent oxidizing properties. Our research focuses on the hemibiotrophic fungal wheat pathogen Zymoseptoria tritici, enabling us to investigate host-pathogen interactions. We examined two catalase-peroxidase (CP) genes, ZtCpx1 and ZtCpx2, to elucidate how Z. tritici deals with host-generated H2O2 during infection. Our analysis revealed that ZtCpx1 was up-regulated during biotrophic growth and asexual spore formation in vitro, while ZtCpx2 showed increased expression during the transition from biotrophic to necrotrophic growth and in-vitro vegetative growth. Deleting ZtCpx1 increased the mutant's sensitivity to exogenously added H2O2 and significantly reduced virulence, as evidenced by decreased Septoria tritici blotch symptom severity and fungal biomass production. Reintroducing the wild-type ZtCpx1 allele with its native promoter into the mutant strain restored the observed phenotypes. While ZtCpx2 was not essential for full virulence, the ZtCpx2 mutants exhibited reduced fungal biomass development during the transition from biotrophic to necrotrophic growth. Moreover, both CP genes act synergistically, as the double knock-out mutant displayed a more pronounced reduced virulence compared to ΔZtCpx1. Microscopic analysis using fluorescent proteins revealed that ZtCpx1 was localized in the peroxisome, indicating its potential role in managing host-generated reactive oxygen species during infection. In conclusion, our research sheds light on the crucial roles of CP genes ZtCpx1 and ZtCpx2 in the defence mechanism of Z. tritici against host-generated hydrogen peroxide.

Safety evaluation of the food enzyme catalase from the non-genetically modified Aspergillus tubingensis strain AE-CN.

The food enzyme catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase; EC 1.11.1.6) is produced with the non-genetically modified Aspergillus tubingensis strain AE-CN by Amano Enzyme Inc. The absence of viable cells of the production organism in the food enzyme was not demonstrated. The food enzyme is intended to be used in five food manufacturing processes: production of baked products, processing of egg and egg products, production of fruit and vegetable products other than juices, production of cheese and production of fish roes. The dietary exposure to the food enzyme total organic solids (TOS) was estimated to be up to 0.325 mg TOS/kg body weight (bw) per day in European populations. The results of the in vitro genotoxicity studies indicated the presence of a clastogenic agent in the food enzyme which could not be dismissed due to limitations in the in vivo studies. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 323 mg TOS/kg bw per day, the highest dose tested. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and one match was found. The Panel considered that the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood is low. Because of the results of the genotoxicity studies, and as the absence of viable cells from the production strain was not demonstrated, the Panel was unable to establish the safety of the food enzyme.

Differential diagnosis of disseminated Mycobacterium avium and Mycobacterium tuberculosis infection in HIV patients using duplex PCR.

Background: Disseminated Mycobacterium avium complex (MAC) and Mycobacterium tuberculosis infections have almost similar clinical presentations but require different therapeutic management. Materials & methods: A duplex PCR was designed based on the sequence variation between the genes encoding catalase-peroxidase (KatG) of M. avium complex and M. tuberculosis, so as to discriminate MAC, M. tuberculosis and mixed mycobacterial (MAC + M. tuberculosis) infections in HIV patients. Results: An accurate, single-step differential diagnosis of disseminated mycobacterial infections in HIV patients was achieved with specific detection of a single band each for M. avium (120 bp) and M. tuberculosis (90 bp) and two bands for the mixed (120 and 90 bp) infections. Conclusion:katG gene-based duplex PCR can facilitate quick differential diagnosis of disseminated MAC and M. tuberculosis infections in HIV patients.

The Richness and Diversity of Catalases in Bacteria.

Catalases play a key role in the defense against oxidative stress in bacteria by catalyzing the decomposition of H2O2. In addition, catalases are also involved in multiple cellular processes, such as cell development and differentiation, as well as metabolite production. However, little is known about the abundance, diversity, and distribution of catalases in bacteria. In this study, we systematically surveyed and classified the homologs of three catalase families from 2,634 bacterial genomes. It was found that both of the typical catalase and Mn-catalase families could be divided into distinct groups, while the catalase-peroxidase homologs formed a tight family. The typical catalases are rich in all the analyzed bacterial phyla except Chlorobi, in which the catalase-peroxidases are dominant. Catalase-peroxidases are rich in many phyla, but lacking in Deinococcus-Thermus, Spirochetes, and Firmicutes. Mn-catalases are found mainly in Firmicutes and Deinococcus-Thermus, but are rare in many other phyla. Given the fact that catalases were reported to be involved in secondary metabolite biosynthesis in several Streptomyces strains, the distribution of catalases in the genus Streptomyces was given more attention herein. On average, there are 2.99 typical catalases and 0.99 catalase-peroxidases in each Streptomyces genome, while no Mn-catalases were identified. To understand detailed properties of catalases in Streptomyces, we characterized all the five typical catalases from S. rimosus ATCC 10970, the oxytetracycline-producing strain. The five catalases showed typical catalase activity, but possessed different catalytic properties. Our findings contribute to the more detailed classification of catalases and facilitate further studies about their physiological roles in secondary metabolite biosynthesis and other cellular processes, which might facilitate the yield improvement of valuable secondary metabolites in engineered bacteria.

Resistance Reversed in KatG Mutants of Mycobacterium tuberculosis.

A peptidomimetic containing a thiazolo ring-fused 2-pyridone (C10) has now been reported to inhibit hypoxia-induced tolerance to isoniazid (INH) in Mycobacterium tuberculosis (Flentie et al., Proc. Natl. Acad. Sci. U. S. A., 2019). The C10 compound could also potentiate the bactericidal activity in aerobically grown bacilli, prevented selection of drug-resistant strains, and reversed INH resistance in katG (catalase-peroxidase) mutants.

The spatiotemporal control of KatG2 catalase-peroxidase contributes to the invasiveness of Fusarium graminearum in host plants.

Reactive oxygen species (ROS) are involved in the pathogen-host interactions, and play a Janus-faced role in the resistance and susceptibility of plants to biotrophic and necrotrophic pathogens. The ascomycete fungus Fusarium graminearum causes hazardous wheat Fusarium head blight worldwide. Deletion of the putative secreted catalase-peroxidase gene in F. graminearum, KatG2, reduced the virulence in wheat spike infection. However, it remains unclear when and where KatG2 scavenges ROS during the invasion of wheat. In this study, we delineate the change in ROS levels in the transition of the infection phase under microscopic observation. Correspondingly, the pathogen switches its strategy of infection with temporal and spatial regulation of KatG2 to counteract oxidative stress generated by host plant cells. With the native promoter-driven KatG2-mRFP strain, we show that KatG2-mRFP expression was induced in planta and accumulated in the infection front region at the early infection stage. In contrast to its ubiquitous cellular localization in runner hyphae, KatG2-mRFP is exclusively located on the cell wall of invading hyphal cells, especially at the pathogen-host cellular interface. Using posttranslational modification analysis, we found that asparagine residues at the 238 and 391 positions of KatG2 could be modified by N-glycosylation and that these two residues are required for KatG2 accumulation and cell wall localization in planta.

Pharmacoinformatics-based identification of anti-bacterial catalase-peroxidase enzyme inhibitors.

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). In the present age, due to the rapid increase in antibiotic resistance worldwide, TB has become a major threat to human life. Regardless of significant efforts have been inclined to improve the healthcare systems for improving diagnosis, treatment, and anticipatory measures controlling TB is challenging. To date, there are no such therapeutic chemical agents available to fight or control the bacterial drug-resistance. The catalase-peroxidase enzyme (katG) which encoded by the katG gene of Mtb is most frequently getting mutated and hence promotes Isoniazid resistance by diminishing the normal activity of katG enzyme. In the current study, an effort has been intended to find novel and therapeutically active antibacterial chemical compounds through pharmacoinformatics methodologies. Initially, the five mutant katG were generated by making mutation of Ser315 by Thr, Ile, Arg, Asn, and Gly followed by structural optimizations. About eight thousand small molecules were collected from the Asinex antibacterial library. All molecules were docked to active site of five mutant katG and wild type katG. To narrow down the chemical space several criteria were imposed including, screening for highest binding affinity towards katG proteins, compounds satisfying various criterion of drug-likeliness properties like Lipinski's rule of five (RO5), Veber's rule, absorption, distribution, metabolism, and excretion (ADME) profile, and synthetic accessibility. Finally, five molecules were found to be important antibacterial katG inhibitors. All the analyzed parameters suggested that selected molecules are promising in nature. Binding interactions analysis revealed that proposed molecules are efficient enough to form a number of strong binding interactions with katG proteins. Dynamic behavior of the proposed molecules with katG protein was evaluated through 100 ns molecular dynamics (MD) simulation study. Parameters calculated from the MD simulation trajectories adjudged that all molecules can form stable complexes with katG. High binding free energy of all proposed molecules definitely suggested strong affection towards the katG. Hence, it can be concluded that proposed molecules might be used as antibacterial chemical component subjected to experimental validation.

First in vivo Evidence That Glutathione-S-Transferase Operates in Photo-Oxidative Stress in Cyanobacteria.

Although glutathione (GSH) and GSH-dependent enzymes, such as glutathione transferases (GSTs), are thought to have been developed by cyanobacteria to cope with the reactive oxygen species (ROS) that they massively produced by their active photosynthesis, there had been no in vivo analysis of the role of GSTs in cyanobacteria so far. Consequently, we have analyzed two of the six GSTs of the model cyanobacterium Synechocystis PCC 6803, namely Sll1545 (to extend its in vitro study) and Slr0236 (because it is the best homolog to Sll1545). We report that Sll1545 is essential to cell growth in standard photo-autotrophic conditions, whereas Slr0236 is dispensable. Furthermore, both Sll1545 and Slr0236 operate in the protection against stresses triggered by high light, H2O2, menadione and methylene blue. The absence of Slr0236 and the depletion of Sll1545 decrease the tolerance to methylene blue in a cumulative way. Similarly, the combined absence of Slr0236 and depletion of Sll1545 decrease the resistance to high light. Attesting their sensitivity to high-light or methylene blue, these Δslr0236-sll1545 cells transiently accumulate ROS, and then reduced and oxidized glutathione in that order. In contrast, the absence of Slr0236 and the depletion of Sll1545 increase the tolerance to menadione in a cumulative way. This increased menadione resistance is due, at least in part, to the higher level of catalase and/or peroxidase activity of these mutants. Similarly, the increased H2O2 resistance of the Δslr0236-sll1545 cells is due, at least in part, to its higher level of peroxidase activity.

Studies on peroxidase production and detection of Sporotrichum thermophile-like catalase-peroxidase gene in a B acillus species isolated from Hogsback forest reserve, South Africa.

This study sought to determine the process conditions for optimum peroxidase production by a B acillus species (Bacillus sp. FALADE-1-KX640922) isolated from Hogsback forest reserve in South Africa and characterize the peroxidase gene in the bacteria. We optimized peroxidase production by manipulating the environmental and nutritional parameters under submerged fermentation. Subsequently, the gene encoding heme-peroxidase was determined through nested polymerase chain reaction and Sanger DNA sequencing. The studied bacteria had maximum peroxidase production at pH 8, 30 °C and 150 rpm. The addition of guaiacol to lignin fermentation medium enhanced peroxidase production by over 100 % in the studied bacteria. However, the other lignin monomers (veratryl alcohol, vanillin, vanillic acid and ferulic acid) repressed the enzyme activity. Modification of the fermentation medium with ammonium sulphate gave the maximum peroxidase yield (8.87 U mL-1). Under the predetermined culture conditions, Bacillus sp. FALADE-1 expressed maximum specific peroxidase activity at 48 h (8.32 U mg-1). Interestingly, a search of the sequenced gene in PeroxiBase showed 100% similarity to Sporotrichum thermophile catalase-peroxidase gene (katG), as well, the deduced protein sequence clustered with bacterial catalase-peroxidases and had a molecular weight of about 11.45 kDa with 7.01 as the estimated isoelectric point. Subsequently, the nucleotide sequence was deposited in the National Center for Biotechnology Information (NCBI) repository with the accession number MF407314. In conclusion, Bacillus sp. FALADE-1 is a promising candidate for improved peroxidase production.

Molecular dynamics simulation and binding free energy studies of novel leads belonging to the benzofuran class inhibitors of Mycobacterium tuberculosis Polyketide Synthase 13.

In this work, the binding mechanism of new Polyketide Synthase 13 (Pks13) inhibitors has been studied through molecular dynamics simulation and free energy calculations. The drug Tam1 and its analogs, belonging to the benzofuran class, were submitted to 100 ns simulations, and according to the results obtained for root mean square deviation, all the simulations converged from approximately 30 ns. For the analysis of backbone flotation, the root mean square fluctuations were plotted for the Cα atoms; analysis revealed that the greatest fluctuation occurred in the residues that are part of the protein lid domain. The binding free energy value (ΔGbind) obtained for the Tam16 lead molecule was of -51.43 kcal/mol. When comparing this result with the ΔGbind values for the remaining analogs, the drug Tam16 was found to be the highest ranked: this result is in agreement with the experimental results obtained by Aggarwal and collaborators, where it was verified that the IC50 for Tam16 is the smallest necessary to inhibit the Pks13 (IC50 = 0.19 µM). The energy decomposition analysis suggested that the residues which most interact with inhibitors are: Ser1636, Tyr1637, Asn1640, Ala1667, Phe1670, and Tyr1674, from which the greatest energy contribution to Phe1670 was particularly notable. For the lead molecule Tam16, a hydrogen bond with the hydroxyl of the phenol not observed in the other analogs induced a more stable molecular structure. Aggarwal and colleagues reported this hydrogen bonding as being responsible for the stability of the molecule, optimizing its physic-chemical, toxicological, and pharmacokinetic properties.

Molecular Analysis of katG Encoding Catalase-Peroxidase from Clinical Isolate of Isoniazid-Resistant Mycobacterium tuberculosis.

Isoniazid (INH) is a drug for the treatment of tuberculosis in patients infected with Mycobacterium tuberculosis. The katG enzyme, or catalase-peroxidase, activates the pro-drug INH that is coded by the katG gene in M. tuberculosis. Mutations of the katG gene in M. tuberculosis are a major INH resistance mechanism. The M. tuberculosis clinical isolate R2 showed INH resistance at a high level of 10 µg/mL. However, the molecular basis for the resistance is unclear. The identification of a mutation in the katG gene of the clinical isolate R2 showed four mutations, i.e., C1061T, G1261 A, G1388T, G2161A, which correspond to the amino acid substitutions T354I, G421S, R463L, and V721M, respectively. The mutant katG gene, along with the wild-type were cloned, expressed and purified. The mutant enzyme showed 86.5% of catalase and 45% of peroxidase activities in comparison to the wild type. The substitutions of T354I and G421S in mutant katG R2 created significant instability in the adduct triad complex (Trp107-Tyr229-Met255), a part of the active site of the catalase-peroxidase enzyme in the model structure analysis. The events could be based on the high resistance of the clinical isolate R2 toward INH as the molecular basis.

Peculiar genes for thermostable bifunctional catalase-peroxidases in Chaetomium thermophilum and their molecular evolution.

Catalase-peroxidases represent one important subfamily of ancestral antioxidant enzymes originally evolved in bacteria for the protection against various forms of oxidative stress. KatG genes coding for these bifunctional catalase-peroxidases were during their peculiar evolution transferred from Bacteroidetes to the fungal phylum Ascomycota via a horizontal gene transfer event. Here we analyse a newly discovered fungal katG gene without introns coding for a thermostable catalase-peroxidase from Chaetomium thermophilum var. dissitum and compare it with closely related thermophilic and mesophilic katGs and their translation products. We show that CthediskatG gene resembling its bacterial counterparts has a typical eukaryotic transcription start site and also contains a conserved eukaryotic polyadenylation signal behind its 3' terminus. Moreover, we have detected polyA tails in corresponding transcripts of katG from two different mRNA libraries of C. thermophilum var. disstum. Although otherwise highly conserved, only in katG genes of two C. thermophilum variants a unique 60 bp long deletion leading in the translated product with high probability to a modified loop and thus access to the prosthetic heme group was observed. We also present an updated molecular phylogeny revealing the evolutionary position of fungal thermostable catalase-peroxidases within a robust phylogenetic tree of the whole KatG subfamily.