Ceratocystiopsis: a reappraisal based on molecular criteria

The compact mitogenome of Ceratocystiopsis pallidobrunnea

Ceratocystiopsis is a fungal genus that has been assigned to the Ophiostomatales, fungi known for their association with various bark beetles and other arthropods. The mitochondrial genome of Ceratocystiopsis pallidobrunnea has been characterized and compared with other members of the genus Ceratocystiopsis and Ophiostomatales. At 29 022 bp, the mitogenome of C. pallidobrunnea is the smallest reported so far for this genus. Gene arrangement was observed to be conserved for this group of fungi and mitogenome variation appears to be mostly due to the absence and presence of introns. The long-term goal is to apply mitogenomes to resolve taxonomic issues within the Ophiostomatales and within the various genera that comprise the Ophiostomataceae.

Ceratocystiopsis spp. associated with pine- and spruce-infesting bark beetles in Norway

The genus Ceratocystiopsis (Ophiostomatales, Ascomycota) includes 21 species, which can be found mainly in association with bark beetles in the Northern Hemisphere. A survey of Ceratocystiopsis species associated with bark beetles infesting Picea abies and Pinus sylvestris in Norway yielded 126 isolates, representing Ceratocystiopsis neglecta and Ceratocystiopsis rollhanseniana, and four species described herein as Ceratocystiopsis chalcographii, Ceratocystiopsis debeeria, Ceratocystiopsis norroenii and Ceratocystiopsis troendelagii. The new taxa were morphologically characterised and phylogenetically analysed on the basis of sequence data of multiple loci (ITS, LSU, beta-tubulin (TUB2), calmodulin (CAL) and translation elongation factor 1-alpha (TEF1) genes). Ceratocystiopsis norroenii and C. rollhanseniana were the most frequently isolated species, and the latter species had the wider vector range.

Morphological and Phylogenetic Analyses Reveal a New Species of Ceratocystiopsis (Ophiostomataceae, Ophiostomatales) Associated with Ips subelongatus in Inner Mongolia (China) with Weak Host Pathogenicity

Ophiostomatoid fungi are known for their associations with bark beetles, and some species are important sources of tree diseases. Ceratocystiopsis is a genus of the ophiostomatoid fungi in order Ophiostomatales. The shortage of DNA barcodes for many species in this genus has resulted in the presence of many unnamed cryptic species. In this study, Ceratocystiopsis subelongati sp. nov. associated with Ips subelongatus infesting Pinus sylvestris var. mongolica in Inner Mongolia, China, was identified and described based on phylogenetic inference of multi-gene DNA sequences and morphological characteristics. The species is characterized by a hyalorhinocladiella- to sporothrix-like asexual state and an optimal growth temperature of 30 °C. Artificial inoculation tests in the field showed that it is mildly pathogenic to five-year-old larch trees, the main host of I. subelongatus. It is also the first described Ceratocystiopsis species associated with I. subelongatus in China. This discovery should provide new avenues for studying the symbiosis between bark beetles and ophiostomatoid fungi.

The diversity of mtDNA rns introns among strains of Ophiostoma piliferum, Ophiostoma pluriannulatum and related species

Background

Based on previous studies, it was suspected that the mitochondrial rns gene within the Ophiostomatales is rich in introns. This study focused on a collection of strains representing Ophiostoma piliferum, Ophiostoma pluriannulatum and related species that cause blue-stain; these fungi colonize the sapwood of trees and impart a dark stain. This reduces the value of the lumber. The goal was to examine the mtDNA rns intron landscape for these important blue stain fungi in order to facilitate future annotation of mitochondrial genomes (mtDNA) and to potentially identify mtDNA introns that can encode homing endonucleases which may have applications in biotechnology.

Results

Comparative sequence analysis identified five intron insertion sites among the ophiostomatoid fungi examined. Positions mS379 and mS952 harbor group II introns, the mS379 intron encodes a reverse transcriptase, and the mS952 intron encodes a potential homing endonuclease. Positions mS569, mS1224, and mS1247 have group I introns inserted and these encode intact or eroded homing endonuclease open reading frames (ORF). Phylogenetic analysis of the intron ORFs showed that they can be found in the same insertion site in closely and distantly related species.

Conclusions

Based on the molecular markers examined (rDNA internal transcribed spacers and rns introns), strains representing O. pilifera, O. pluriannulatum and Ophiostoma novae-zelandiae could not be resolved. Phylogenetic studies suggest that introns are gained and lost and that horizontal transfer could explain the presence of related intron in distantly related fungi. With regard to the mS379 group II intron, this study shows that mitochondrial group II introns and their reverse transcriptases may also follow the life cycle previously proposed for group I introns and their homing endonucleases. This consists of intron invasion, decay of intron ORF, loss of intron, and possible reinvasion.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-3076-6) contains supplementary material, which is available to authorized users.

Cornuvesica: A little known mycophilic genus with a unique biology and unexpected new species

Little is known about the biology of the monotypic genus Cornuvesica (Microascales), apart from that isolates are notoriously difficult to culture on artificial media. A recent collection of material resembling this genus from freshly made wounds on Gmelina arborea in Indonesia, provided an opportunity to reconsider all available material of Cornuvesica falcata, type species of the genus. In addition to morphological comparisons, multigene phylogenetic analyses were made using sequences of the SSU, ITS, LSU and TEF-1α genes. Our results showed that the holotype of Cor. falcata from pine in Canada differed from all other material previously considered to represent this species and also from the new Indonesian collections. The collections considered represented three additional species that we describe here as new. Three New Zealand isolates and an isolate from UK were respectively described as Cor. acuminata and Cor. crypta, while the Indonesian isolates were described as Cor. magnispora. Phylogenies based on the SSU and LSU data sets showed that Cornuvesica spp. do not belong in the Ceratocystidaceae as previously suggested, but represent a distinct lineage in the Microascales that has yet to be named. Results showed that culture filtrates from other fungi or ferric chloride markedly stimulated the growth of Cor. magnispora.

Ecological and Evolutionary Determinants of Bark Beetle -Fungus Symbioses

Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree of mutual dependence among the beetles and their fungal partners. Unfortunately, the processes that shaped current day beetle-fungus symbioses remain poorly understood. Phylogeny, the degree and type of dependence on partners, mode of transmission of symbionts (vertical vs. horizontal), effects of the abiotic environment, and interactions among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I provide an overview of these associations and discuss how evolution and ecological processes acted in concert to shape these fascinating, complex symbioses.

Associations of Conifer-Infesting Bark Beetles and Fungi in Fennoscandia

Bark beetles (Coleoptera, Scolytinae) have a widespread association with fungi, especially with ophiostomatoid fungi (Ascomycota) that cause blue staining of wood, and in some cases, serious tree diseases. In Fennoscandia, most studies of these fungi have focused on economically important bark beetle species and this is likely to have led to a biased view of the fungal biodiversity in the region. Recently, the associations between fungi and bark beetles in Fennoscandia have been shown to be more diverse than previously thought. Furthermore, they form complex and dynamic associations that are only now beginning to emerge. This review examines the current knowledge of the rather poorly known interactions between bark beetles, fungi and their conifer host trees in Fennoscandia. The diversity of ophiostomatoid species is discussed and the possible factors that influence the assemblages of fungal associates are considered for all species that are known to occur in the region. For many ophiostomatoid species found in Fennoscandia, little or nothing is known regarding their pathogenicity, particularly if they were to be transferred to new environments. We, therefore, draw attention to the possible threats of timber trade and climate change-induced invasions of new habitats by bark beetles and the fungi that can be moved along with them.

Multi-gene phylogenies define Ceratocystiopsis and Grosmannia distinct from Ophiostoma

Ophiostoma species have diverse morphological features and are found in a large variety of ecological niches. Many different classification schemes have been applied to these fungi in the past based on teleomorph and anamorph features. More recently, studies based on DNA sequence comparisions have shown that Ophiostoma consists of different phylogenetic groups, but the data have not been sufficient to define clear monophyletic lineages represented by practical taxonomic units. We used DNA sequence data from combined partial nuclear LSU and β-tubulin genes to consider the phylogenetic relationships of 50 Ophiostoma species, representing all the major morphological groups in the genus. Our data showed three well-supported, monophyletic lineages in Ophiostoma. Species with Leptographium anamorphs grouped together and to accommodate these species the teleomorph-genus Grosmannia (type species G. penicillata), including 27 species and 24 new combinations, is re-instated. Another well-defined lineage includes species that are cycloheximide-sensitive with short perithecial necks, falcate ascospores and Hyalorhinocladiella anamorphs. For these species, the teleomorph-genus Ceratocystiopsis (type species O. minuta), including 11 species and three new combinations, is re-instated. A third group of species with either Sporothrix or Pesotum anamorphs includes species from various ecological niches such as Protea infructescences in South Africa. This group also includes O. piliferum, the type species of Ophiostoma, and these species are retained in that genus. Ophiostoma is redefined to reflect the changes resulting from new combinations in Grosmannia and Ceratocystiopsis. Our data have revealed additional lineages in Ophiostoma linked to morphological characters. However, these species are retained in Ophiostoma until further data for a larger number of species can be obtained to confirm monophyly of the apparent lineages.

Ophiostomatoid fungi associated with the northern spruce engraver, Ips perturbatus, in western Canada

A number of ophiostomatoid fungi were isolated from the spruce-infesting bark beetle, Ips perturbatus and its galleries collected from felled spruce trees and logs in northern BC and the Yukon Territory. Isolates were identified to species using morphological characteristics, nuclear ribosomal DNA and partial beta-tubulin gene sequences. Thirteen morphological and phylogenetic species were identified among the isolates. Leptographium fruticetum, Leptographium abietinum, Ophiostoma bicolor, Ophiostoma manitobense, O. piceaperdum, and eight undescribed species of the genus Ophiostoma and the anamorph genera Leptographium, Hyalorhinocladiella, Ambrosiella and Graphium. A number of these species, i.e. L. fruticetum, Hyalorhinocladiella sp. 2, O. bicolor and O. manitobense, were isolated repeatedly from I. perturbatus, while others, i.e. Graphium sp. 1 and O. piceaperdum, seemed to be sporadic associates. Among all the isolates, L. fruticetum had the highest relative dominance in this survey. A high frequency of occurrence of this species with the beetle may indicate a specific relationship between the two partners.

Phylogenetic analysis of the bluestain fungus Ophiostoma minus based on partial ITS rDNA and beta-tubulin gene sequences

In an attempt to clarify the relationship between fungi classified as Ophiostoma minus, but of different geographic origins and mating systems, sequencing of the 5.8S and ITS 2 rDNA, and beta-tubulin gene was carried out. The beta-tubulin gene was highly informative, supporting the sub-division of O. minus into two groups based on geographic origin. Furthermore, isolates previously classified as O. pseudotsugae were confirmed as being clearly distinct from O. minus. However, sequencing did not reveal any polymorphisms between isolates with homothallic as compared to heterothallic mating systems. This was supported by crosses using methylbenzamidazole-2-yl carbamate nuclear markers which showed that hybridisation between isolates of different mating systems was possible. However, we propose that different mating systems may still signal a divergence of isolates of O. minus.

The nuclear small subunit ribosomal genes of Sphaeronaemella helvellae, Sphaeronaemella fimicola, Gabarnaudia betae, and Cornuvesica falcata: phylogenetic implications

Sequences were obtained from the nuclear small subunit ribosomal RNA genes for representatives of four ophiostomatoid genera (Ceratocystis, Gondwanamyces, Cornuvesica, and Sphaeronaemella) to resolve their phylogenetic position within the Ascomycota. Phylogenetic analysis suggests that these genera are monophyletic and share common ancestry with members of the Microascales. Based on sequence data, strains representing the mitotic species Gabarnaudia betae (Delacr.) Samson & W. Gams were shown clearly to be derived from Sphaeronaemella species. Sequences were also obtained from strains representing the syntype of Sphaeronaemella fragariae, the exholotype of Sphaeronaemella humicola, and the extype of Gabarnaudia tholispora. The results suggest that putative extype cultures for S. humicola and G. tholispora no longer represent the original material deposited. Our data also support the exclusion of S. fragariae from Sphaeronaemella. Key words: Cornuvesica, Gabarnaudia, Gondwanamyces, Sphaeronaemalla fragariae, ophiostomatoid fungi, ribosomal DNA.

A group I intron-like sequence in the nuclear small ribosomal subunit gene of the ophiostomatoid fungus Gondwanamyces proteae

During a phylogenetic study of ophiostomatoid fungi, a group I intron-like sequence was noted in the SSU rDNA gene of Gondwanamyces proteae. Secondary structure and sequence characteristics assigned the intron to the I E class. We then examined 27 related Group I-like sequences deposited in GenBank, and as a result 15 additional and previously uncategorized I E rDNA introns were identified. This study, with other recent publications, suggests that the I E class might represent a major family of group I introns that are located within the nuclear SSU and, to some extent LSU, genes in fungi.

Notes on Ceratocystis brunnea and some other Ophiostoma species based on partial ribosomal DNA sequence analysis

Ribosomal gene sequence data were obtained from a nonfruiting culture originally identified as Ceratocystis brunnea R.W. Davidson; this species was considered a nomen dubium by Upadhyay (1981) due to a presumptive lack of teleomorph material. The data showed that C. brunnea is a valid species that should be transferred to Ophiostoma, demonstrating that DNA data can compensate for the presumed or actual lack of morphological features lost during either long-term culturing or disintegration of holotype specimens. Use of partial large ribosomal sequence data to assess the relationship of C. brunnea to other Ophiostoma spp. showed that it is not a synonym of Ophiostoma piliferum (Fr.:Fr.) Syd. & P. Syd. as has been suggested; instead, it appears to be distantly related to Ophiostoma piceae (Münch) Syd. & P. Syd. The data obtained for the Ophiostoma piliferum strains included in this study suggest that hardwood-derived isolates may be distinct from those obtained from conifers. In addition, molecular characters support transferring Ceratocystis pseudonigra Olchow. & Reid, Ceratocystiopsis concentrica (Olchow. & Reid) Upadhyay, Ceratocystiopsis pallidobrunnea (Olchow. & Reid) Upadhyay, and Ceratocystiopsis crenulata (Olchow. & Reid) Upadhyay to Ophiostoma.Key words: rDNA, phylogenetics, Ophiostoma piliferum, Ophiostoma, Ceratocystsis.

Three new species of Ophiostoma and notes on Cornuvesica falcata

Sampling of beetles, beetle galleries, and stained tree tissues by ourselves and others to obtain isolates of ophiostomatoid fungal species yielded three Ceratocystiopsis-like entities. Using partial rDNA sequences, these were previously identified as being different from both each other and all other described species of Ceratocystiopsis and Ophiostoma. As Ceratocystiopsis Upadhyay et Kendrick has been reduced to synonymy with Ophiostoma Syd. et P. Syd., and sufficient dried material is now available, these are described herein as Ophiostoma carpenteri sp. nov., Ophiostoma rollhansenianum sp. nov., and Ophiostoma manitobense sp. nov. We found O. carpenteri to be closely related to Ophiostoma retusum (R.W. Davidson et T.E. Hinds) Hausner et al., and that both species may actually be fungal symbionts and could represent a discrete genus. Although morphologically O. rollhansenianum appears similar to Ophiostoma minutum Siemaszko, a clearly variable species, and O. manitobense to Ophiostoma minus (Hedgc.) Syd. et P. Syd., earlier rDNA data indicate that O. rollhansenianum and O. manitobense are actually more closely related to Ophiostoma coliferum (Marmolejo et Butin) Hausner et al., and Ophiostoma ranaculosum (J.R. Bridges et T.J. Perry) Hausner et al. We also comment on some morphological features that have previously been overlooked or misreported in Cornuvesica falcata (E.F. Wright et Cain) C.D. Viljoen et al., such as the ascospores actually being hyaline and the presence of two distinct Chalara anamorphs.Key words: Ophiostoma, molecular and morphological criteria, Ceratocystiopsis, Cornuvesica.

Phylogenetic relationships in Leptographium based on morphological and molecular characters

Species of Leptographium Lagerberg & Melin are characterized by mononematous conidiophores with dark stipes and conidiogenous apparatuses with complex series of branches. These fungi generally inhabit woody substrates, are associated with bark beetles (Coleoptera: Scolytidae) and cause blue-stain in conifers. Few phylogenetic studies have been conducted on Leptographium species, and those that have been undertaken have been focused on a small number of species. The objective of this study was to investigate the phylogenetic relationships among species in Leptographium based on partial DNA operon sequences and to ascertain whether morphological characters are congruent with DNA-based phylogeny. Morphological characters were analyzed and compared with results from DNA sequence analysis. Results indicate that there are three groups within Leptographium based on DNA sequence analysis. There was, however, no congruence between these groups and those emerging from morphological characters. Data from this study strongly support the connection between Leptographium and Ophiostoma Sydow & Sydow. They also provide us with an objective means to confirm the identity of many Leptographium species that are difficult to distinguish based on morphological characters.Key words: Leptographium, phylogeny, morphology, Ophiostoma, rRNA.

On the phylogeny of members of Ceratocystis s.s. and Ophiostoma that possess different anamorphic states, with emphasis on the anamorph genus Leptographium, based on partial ribosomal DNA sequences

Phylogenetic analysis of partial ribosomal DNA sequences was undertaken to assess the phylogenetic distribution of ophiostomatoid anamorphs with an emphasis on members of Leptographium and the generic limits of Ceratocystis sensu lato Ell. & Halst. Molecular data identified one group of Ophiostoma species with anamorphs assignable to Pesotum and Leptographium that appears to be monophyletic. This study also showed that, based on molecular characters, Pesotum pini (Hutchison & Reid) Okada and all Leptographium strains tested, including L. terebrantis Barras & Perry, L. lundbergii Lag. & Melin, and L. procerum (Kendr.) Wingf., could be placed among Ophiostoma species. With regard to the anamorphs of Ophiostoma, we determined that the separation of Leptographium from Pesotum, although convenient, is artificial. The partial ribosomal DNA sequences also confirm that Europhium should be considered a synonym of Ophiostoma. The phylogenetic position of species of Ceratocystis sensu lato with Chalara-like, Knoxdaviesia, and Gabarnaudia anamorphs is also discussed.Key words: Ceratocystis, Ophiostoma, Leptographium, partial rDNA sequences, phylogeny.

Remersonia, a new genus for Stilbella thermophila, a thermophilic mould from compost

The thermophilic synnematous hyphomycete Stilbella thermophila is redescribed and illustrated based on the study of type and supplementary material. The species is transferred to a new anamorph genus, Remersonia, characterized by determinate synnemata with scarcely branched conidiophores, percurrently proliferating conidiogenous cells, relatively large ameroconidia that accumulate in slime, and thermotolerant growth. Cladistic analysis of partial 18S and 28S ribosomal DNA sequences suggest that the fungus is a member of the Sordariales. Septal ultrastructure and a failure to grow on benomyl-emended media support the ascomycetous affinities of the fungus. Failure to grow on cycloheximide-emended media supports sequencing data suggesting that the species is not allied with the Ophiostomatales. The biology of the fungus is briefly discussed. Key words: thermophilic fungi, mushroom compost, hyphomycetes, systematics, 18S rDNA, 28S rDNA.

Ophiostoma protearum sp.nov. associated with Protea caffra infructescences

A new ophiostomatoid fungus, Ophiostoma protearum, and its Sporothrix anamorph, is described based on isolations from infructescences of Protea caffra. The species is compared with ophiostomatoid fungi previously described from Protea infructescences in the Western Cape Province of South Africa. Based on differences in their anamorphs, there appear to be two evolutionary lines among these fungi in this niche. Key words: Ceratocystis, Ceratocystiopsis, Ophiostoma protearum, Sporothrix, Knoxdaviesia, biogeography.

DNA and ascomycete systematics

Present knowledge of different types of RNAs as phylogenetic markers among the fungi is discussed, and examples of phylogenetically informative 18S rRNA signature sequences are given. Such signatures give phylogenetic information that is not provided by parsimony or distance analyses of longer gene sequences. A single signature cannot be used as a decisive criterion for defining taxa, but signature sequences give invaluable hints on phylogenetic relationships and can be included in data matrices as morphological criteria when using parsimony analysis. Key words: DNA, ascomycete phylogeny, signature sequences.