Genome sequence of the filamentous soil fungus Chaetomium cochliodes reveals abundance of genes for heme enzymes from all peroxidase and catalase superfamilies

Abstract

Background: The ascomycetous family Chaetomiaceae (class Sordariomycetes) includes numerous soilborn, saprophytic, endophytic and pathogenic fungi which can adapt to various growth conditions and living niches by providing a broad armory of oxidative and antioxidant enzymes.

Results: We release the 34.7 Mbp draft genome of Chaetomium cochliodes CCM F-232 consisting of 6036 contigs with an average size of 5756 bp and reconstructed its phylogeny. We show that this filamentous fungus is closely related but not identical to Chaetomium globosum and Chaetomium elatum. We screened and critically analysed this genome for open reading frames coding for essential antioxidant enzymes. It is demonstrated that the genome of C. cochliodes contains genes encoding putative enzymes from all four known heme peroxidase superfamilies including bifunctional catalase-peroxidase (KatG), cytochrome c peroxidase (CcP), manganese peroxidase, two paralogs of hybrid B peroxidases (HyBpox), cyclooxygenase, linoleate diol synthase, dye-decolorizing peroxidase (DyP) of type B and three paralogs of heme thiolate peroxidases. Both KatG and DyP-type B are shown to be introduced into ascomycetes genomes by horizontal gene transfer from various bacteria. In addition, two putative large subunit secretory and two small-subunit typical catalases are found in C. cochliodes. We support our genomic findings with quantitative transcription analysis of nine peroxidase & catalase genes.

Conclusions: We delineate molecular phylogeny of five distinct gene superfamilies coding for essential heme oxidoreductases in Chaetomia and from the transcription analysis the role of this antioxidant enzymatic armory for the survival of a peculiar soil ascomycete in various harsh environments.

Keywords: Chaetomium cochliodes; Heme-catalase super family; Peroxidase-catalase superfamily; Peroxidase-chlorite dismutase superfamily; Peroxidase-cyclooxygenase superfamily; Peroxidase-peroxygenase superfamily.

Fig. 1

Phylogenetic relationship among 34 Ascomycetes reconstructed from the conserved region spanning 18S-ITS1-5.8S-ITS2-28S rDNA genes. Maximum likelihood method from MEGA6 with 1000 bootstraps and MrBayes method over 200,000 generations were applied on the same DNA sequence alignment 2,474 bp long (Additional file 2: Figure S1). Bootstrap values above 50 & posterior probabilities are shown, respectively. Scale bare represents the frequency of ML substitutions

Fig. 2

Reconstructed phylogeny of the peroxidase-catalase superfamily with focus on newly sequenced Chaetomia ORFs. The complete tree from 632 full length sequences with 536 sites aligned is presented with collapsed branches that do not contain any Chaetomia sequences. Distinct subfamilies are labelled in different colours. C. cochliodes sequences are labelled red. Values in nodes represent bootstrap values above 50 (from maximum likelihood analysis) and posterior probabilities (from Mr. Bayes), respectively. Abbreviations of peroxidase names are listed in Additional file 3: Table S2. Abbreviations of taxa: Pb, Proteobacteria; As, Ascomycota; Ba, Basidiomycota; Chy, Chytridiomycota; St, Stramenopiles; Chl, Chlorophyta; Vi, Viridiplantae

Fig. 3

Presentation of the promoter region for CcochkatG gene showing typical eukaryotic regulatory elements for a HGT-related bacterial gene. Sequence analysis was performed in Contig 0012 between positions 43,000 - 47,000 with FGENESH software [14], drawn to scale

Fig. 4

Reconstructed phylogeny of the peroxidase-cyclooxygenase superfamily with focus on Chaetomia ORFs. The complete tree from 204 full length sequences with 1,053 aligned sites is presented. C. cochliodes sequences are labelled red. Distinct subfamilies are labelled in different colours. Values in nodes represent bootstrap values above 50 (from maximum likelihood analysis) and posterior probabilities (from Mr. Bayes), respectively. Abbreviations of peroxidase names are listed in Additional file 5: Table S3. Abbreviations of taxa: Ac, Actinobacteria; Acb, Acidobacteria; Cy, Cyanobacteria; Prb, Proteobacteria; Plb, Planctomycetes (bacteria); As, Ascomycota; Ba, Basidiomycota; Mu, Mucoromycota; St, Stramenopiles; Cn, Cnidaria; De, Deuterostomia

Fig. 5

Reconstructed phylogeny of the peroxidase-dismutase superfamily with focus on newly discovered Chaetomia sequences forming a separate clade of DyP-Bs together with fused bacterial representatives from which they were derived by a HGT event. The complete tree from 282 full length sequences is presented with 655 sites aligned. C. cochliodes sequence is labelled red. Distinct subfamilies are labelled in different colours. Values in nodes represent bootstrap values above 50 (from maximum likelihood analysis) and posterior probabilities (from Mr. Bayes), respectively. Abbreviations of peroxidase names are listed in Additional file 6: Table S4. Abbreviations of taxa: vir, DNA viruses; Ac, Actinobacteria; Aci, Acidobacteria; Bi, Bacteroidetes; Chl, Chloroflexi (bacteria); Cy, Cyanobacteria; Dei, Deinococci; Fi, Firmicutes; Pb, Proteobacteria; Pmc, Planctomycetes; As, Ascomycota; Ba, Basidiomycota; Alv, Alveolata; Amb, Ameboflagellates; De, Deuterostomia; Mol, Mollusca

Fig. 6

Phylogeny of the peroxidase-peroxygenase superfamily representing numerous gene paralogs of this superfamily among Chaetomiaceae. The complete tree from 172 full length sequences is presented with 287 sites aligned. C. cochliodes paralogs are labelled red. Distinct subfamilies are labelled in different colours. Values in nodes represent bootstrap values above 50 (from maximum likelihood analysis) and posterior probabilities (from Mr. Bayes), respectively. Abbreviations of peroxidase names are listed in Additional file 7: Table S5. Abbreviations of taxa: As, Ascomycota; Ba, Basidiomycota; Mu, Mucoromycota; St, Stramenopiles

Fig. 7

Reconstructed phylogeny of the heme catalase super family with focus on Clade 2 and 3 representing the distribution of Ascomycetous large subunit as well as small subunit catalases (labelled in different colors). The complete tree from 222 full length sequences is presented with 546 sites aligned. C. cochliodes paralogs are labelled red. Distinct clades are labelled in different colours. Values in nodes represent bootstrap values above 50 (from maximum likelihood analysis) and posterior probabilities (from Mr. Bayes), respectively. Abbreviations of peroxidase names are listed in Additional file 8: Table S6. Abbreviations of taxa: Ar, Archaea; Ac, Actinobacteria; Aci, Acidobacteria; Bi, Bacteroidetes; Chl, Chloroflexi (bacteria); Cy, Cyanobacteria; Dei, Deinococci; Fi, Firmicutes; Pb, Proteobacteria; Pmc, Planctomycetes; As, Ascomycota; Ba, Basidiomycota; Chy, Chytridiomycota; Zy, Zygomycota; Cn, Cnidaria; Ich, Ichthyosporea; Chlph, Chlorophyta; BMagno, basal Magnoliophyta; My, Mycetozoa; Cryp, Cryptogams, Eudi, Eudicotyledons, Mctd, Monocotyledons; De, Deuterostomia; Ec, Ecdysozoa