Some Xylaria species on termite nests

Trichoderma-derived pentapeptides from the infected nest mycobiome of the subterranean termite Coptotermes testaceus

Termites live in a dynamic environment where colony health is strongly influenced by surrounding microbes. However, little is known about the mycobiomes of lower termites and their nests, and how these change in response to disease. Here we compared the individual and nest mycobiomes of a healthy subterranean termite colony (Coptotermes testaceus) to one infected and ultimately eradicated by a fungal pathogen. We identified Trichoderma species in the materials of both nests, but they were also abundant in the infected termites. Methanolic extracts of Trichoderma sp. FHG000531, isolated from the infected nest, were screened for secondary metabolites by UHPLC‐HR MS/MS‐guided molecular networking. We identified many bioactive compounds with potential roles in the eradication of the infected colony, as well as a cluster of six unknown peptides. The novel peptide FE011 was isolated and characterized by NMR spectroscopy. The function of this novel peptide family as well as the role of Trichoderma species in dying termite colonies therefore requires further investigation.

Antioxidant Activity and Cytotoxicity against Cancer Cell Lines of the Extracts from Novel Xylaria Species Associated with Termite Nests and LC-MS Analysis

Xylaria species associated with termite nests or soil have been considered rare species in nature and the few which have been reported upon have been found to act as a rich source of bioactive metabolites. This study evaluated 10 ethyl acetate extracts of five new Xylaria species associated with termite nests or soil for their antioxidant activity, and cytotoxicity against different cancer and normal cell lines. DPPH and ABTS radical scavenging activities of the extracts demonstrated strong capacity with low IC₅₀ values. The highest observed activities belonged to X. vinacea SWUF18-2.3 having IC₅₀ values of 0.194 ± 0.031 mg/mL for DPPH assay and 0.020 ± 0.004 mg/mL for ABTS assay. Total phenolic content ranged from 0.826 ± 0.123 to 3.629 ± 0.381 g GAE/g crude extract which correlated with antioxidant activities. The high total phenolic content could contribute to the high antioxidant activities. Cytotoxicity was recorded against A549, HepG2, HeLa and PNT2 and resulted in broad spectrum to specific activity depending on the cell lines. The highest activities were observed with X. subintraflava SWUF16-11.1 which resulted in 11.15 ± 0.32 to 13.17 ± 2.37% cell viability at a concentration of 100 µg/mL. Moreover, LC-MS fingerprints indicated over 61 peaks from all isolates. There were 18 identified and 43 unidentified compounds compared to mass databases. The identified compounds were from various groups of diterpenoids, diterpenes, cytochalasin, flavones, flavonoids, polyphenols, steroids and derivatives, triterpenoids and tropones. These results indicate that Xylaria spp. has abundant secondary metabolites that could be further explored for their therapeutic properties.

Twelve New Taxa of Xylaria Associated with Termite Nests and Soil from Northeast Thailand

Simple Summary

Xylaria species are known for their medicinal value and production of a variety of bioactive compounds. They usually grow on rotten wood, fallen leaves, seeds, and fruits. Some species can be found growing on soil or associated with termite nests, which belong to subgenus Pseudoxylaria. They share with other Xylaria species a suite of morphological characteristics, including conspicuous or massive upright stromata with a light-coloured interior, a longer than wide ascal apical ring, bluing in an iodine reagent, and brown unicellular ascospores possessing a germ slit. In Thailand, there are only limited reports on Xylaria diversity and taxonomy, especially on species associated with termite nests. In the present study, we describe 12 new Xylaria taxa and report two species closely resembling known species from termite nests or soil. Their morphological and cultural characteristics are described and illustrated, and their nucleotide sequences of ITS rDNA, alpha-actin, and beta-tubulin genes were obtained. Phylogenetic inference based on these sequences confirmed that all taxa analyzed belong to subgenus Pseudoxylaria and differ from all other species with sequences available in public databases. Our study is the first to report on the novel Xylaria species associated with termite nests or growing on soil in Thailand. Subgenus Pseudoxylaria is likely highly diverse in the country.

Abstract

The diversity of Xylaria species associated with termite nests in northeast Thailand was investigated. Among the 14 taxa included in this study, 11 species and one variety were described as new, and another two species resemble the existing taxa, X. escharoidea and X. nigripes. The newly described taxa are X. chaiyaphumensis, X. conica, X. fulvescens, X. ischnostroma, X. margaretae, X. minima, X. reinkingii var. microspora, X. siamensis, X. sihanonthii, X. subintraflava, X. thienhirunae, and X. vinacea. Their morphological and cultural characteristics are described and illustrated, and their ITS, α-actin and β-tubulin sequences were analysed. A dichotomous key to the 17 species of Xylaria occurring in Thailand is provided.

You don't have the guts: a diverse set of fungi survive passage through Macrotermes bellicosus termite guts

Background

Monoculture farming poses significant disease challenges, but fungus-farming termites are able to successfully keep their monoculture crop free from contamination by other fungi. It has been hypothesised that obligate gut passage of all plant substrate used to manure the fungal symbiont is key to accomplish this. Here we refute this hypothesis in the fungus-farming termite species Macrotermes bellicosus.

Results

We first used ITS amplicon sequencing to show that plant substrate foraged on by termite workers harbour diverse fungal communities, which potentially could challenge the farming symbiosis. Subsequently, we cultivated fungi from dissected sections of termite guts to show that fungal diversity does not decrease during gut passage. Therefore, we investigated if healthy combs harboured these undesirable fungal genera, and whether the presence of workers affected fungal diversity within combs. Removal of workers led to a surge in fungal diversity in combs, implying that termite defences must be responsible for the near-complete absence of other fungi in functioning termite gardens.

Conclusions

The rapid proliferation of some of these fungi when colonies are compromised indicates that some antagonists successfully employ a sit-and-wait strategy that allows them to remain dormant until conditions are favourable. Although this strategy requires potentially many years of waiting, it prevents these fungi from engaging in an evolutionary arms race with the termite host, which employs a series of complementary behavioural and chemical defences that may prove insurmountable.

Disease-free monoculture farming by fungus-growing termites

Fungus-growing termites engage in an obligate mutualistic relationship with Termitomyces fungi, which they maintain in monocultures on specialised fungus comb structures, without apparent problems with infectious diseases. While other fungi have been reported in the symbiosis, detailed comb fungal community analyses have been lacking. Here we use culture-dependent and -independent methods to characterise fungus comb mycobiotas from three fungus-growing termite species (two genera). Internal Transcribed Spacer (ITS) gene analyses using 454 pyrosequencing and Illumina MiSeq showed that non-Termitomyces fungi were essentially absent in fungus combs, and that Termitomyces fungal crops are maintained in monocultures as heterokaryons with two or three abundant ITS variants in a single fungal strain. To explore whether the essential absence of other fungi within fungus combs is potentially due to the production of antifungal metabolites by Termitomyces or comb bacteria, we performed in vitro assays and found that both Termitomyces and chemical extracts of fungus comb material can inhibit potential fungal antagonists. Chemical analyses of fungus comb material point to a highly complex metabolome, including compounds with the potential to play roles in mediating these contaminant-free farming conditions in the termite symbiosis.

A Laboratory Maintenance Regime for a Fungus-Growing Termite Macrotermes gilvus (Blattodea: Termitidae)

The optimum maintenance conditions of the fungus-growing termite, Macrotermes gilvus (Hagen) (Blattodea: Termitidae), in the laboratory were studied. Termites were kept on a matrix of moist sand and with fungus comb as food. The survival of groups of termites was measured when maintained at different population densities by changing group size and container volume. Larger groups (≥0.6 g) were more vigorous and had significant higher survival rates than smaller groups (≤0.3 g). The population density for optimal survival of M. gilvus is 0.0025 g per container volume (ml) or 0.0169 g per matrix volume (cm(3)), i.e., 1.2 g of termites kept in a 480-ml container filled with 71 cm3 of sand. In termite groups of smaller size (i.e., 0.3 g) or groups maintained in smaller container (i.e., 100 ml) the fungus comb was overgrown with Xylaria spp., and subsequently all termites died within the study period. The insufficient number of workers for regulating the growth of unwanted fungi other than Termitomyces spp. in the fungus comb is the most likely reason. Unlike some other mound-building termite species, M. gilvus showed satisfactory survival when maintained in non-nutritious matrix (i.e., sand). There was no significant difference in the survival rate between different colonies of M. gilvus (n=5), with survival in the range of 78.5-84.4% after 4 wk. Advances in the maintenance of Macrotermes will enable researchers to study with more biological relevance many aspects of the biology, behavior, and management of this species.

Bacterial symbionts in agricultural systems provide a strategic source for antibiotic discovery

As increased antibiotic resistance erodes the efficacy of currently used drugs, the need for new candidates with therapeutic potential grows. Although the majority of antibiotics in clinical use originated from natural products, mostly from environmental actinomycetes, high rediscovery rates, among other factors, have diminished the enthusiasm for continued exploration of this historically important source. Several well-studied insect agricultural systems have bacterial symbionts that have evolved to produce small molecules that suppress environmental pathogens. These molecules represent an underexplored reservoir of potentially useful antibiotics. This report describes the multilateral symbioses common to insect agricultural systems, the general strategy used for antibiotic discovery and pertinent examples from three farming systems: fungus-farming ants, southern pine beetles (SPBs) and fungus-growing termites.

Exploring the potential for actinobacteria as defensive symbionts in fungus-growing termites

In fungus-growing termites, fungi of the subgenus Pseudoxylaria threaten colony health through substrate competition with the termite fungus (Termitomyces). The potential mechanisms with which termites suppress Pseudoxylaria have remained unknown. Here we explore if Actinobacteria potentially play a role as defensive symbionts against Pseudoxylaria in fungus-growing termites. We sampled for Actinobacteria from 30 fungus-growing termite colonies, spanning the three main termite genera and two geographically distant sites. Our isolations yielded 360 Actinobacteria, from which we selected subsets for morphological (288 isolates, grouped in 44 morphotypes) and for 16S rRNA (35 isolates, spanning the majority of morphotypes) characterisation. Actinobacteria were found throughout all sampled nests and colony parts and, phylogenetically, they are interspersed with Actinobacteria from origins other than fungus-growing termites, indicating lack of specificity. Antibiotic-activity screening of 288 isolates against the fungal cultivar and competitor revealed that most of the Actinobacteria-produced molecules with antifungal activity. A more detailed bioassay on 53 isolates, to test the specificity of antibiotics, showed that many Actinobacteria inhibit both Pseudoxylaria and Termitomyces, and that the cultivar fungus generally is more susceptible to inhibition than the competitor. This suggests that either defensive symbionts are not present in the system or that they, if present, represent a subset of the community isolated. If so, the antibiotics must be used in a targeted fashion, being applied to specific areas by the termites. We describe the first discovery of an assembly of antibiotic-producing Actinobacteria occurring in fungus-growing termite nests. However, due to the diversity found, and the lack of both phylogenetic and bioactivity specificity, further work is necessary for a better understanding of the putative role of antibiotic-producing bacteria in the fungus-growing termite mutualistic system.

Xylaria coprinicola, a new species that antagonizes cultivation of Coprinus comatus in China

The species known in China as the chicken-claw fungus is described as a new species, Xylaria coprinicola. This species is known as an antagonist of cultivation of the edible mushroom Coprinus comatus. Stromata of X. coprinicola are cylindrical, terminate in a sterile apex and arise in fascicles from a relative large submerged base; perithecia are immersed and have conspicuously conical ostiolar openings; ascospores are minute. Phylogenetic analyses based on combined partial sequences of rpb2, β-tub and α-act genes showed that X. coprinicola is closely related to those Xylaria species exclusively associated with termite nests.

Phylogenetic status of Xylaria subgenus Pseudoxylaria among taxa of the subfamily Xylarioideae (Xylariaceae) and phylogeny of the taxa involved in the subfamily

To infer the phylogenetic relationships of Xylaria species associated with termite nests within the genus Xylaria and among genera of the subfamily Xylarioideae, beta-tubulin, RPB2, and alpha-actin sequences of 131 cultures of 114 species from Xylaria and 11 other genera of the subfamily were analyzed. These 11 genera included Astrocystis, Amphirosellinia, Discoxylaria, Entoleuca, Euepixylon, Kretzschmaria, Nemania, Podosordaria, Poronia, Rosellinia, and Stilbohypoxylon. We showed that Xylaria species were distributed among three major clades, TE, HY, and PO, with clade TE-an equivalent of the subgenus Pseudoxylaria-encompassing exclusively those species associated with termite nests and the other two clades containing those associated with substrates other than termite nests. Xylaria appears to be a paraphyletic genus, with most of the 11 genera submerged within it. Podosordaria and Poronia, which formed a distinct clade, apparently diverged from Xylaria and the other genera early. Species of Entoleuca, Euepixylon, Nemania, and Rosellinia constituted clade NR, a major clade sister to clade PO, while those of Kretzschmaria were inserted within clade HY and those of Astrocystis, Amphirosellinia, Discoxylaria, and Stilbohypoxylon were within clade PO.

Occurrence of fungi in combs of fungus-growing termites (Isoptera: Termitidae, Macrotermitinae)

Fungus-growing termites cultivate their mutualistic basidiomycete Termitomyces species on a substrate called a fungal comb. Here, the Suicide Polymerase Endonuclease Restriction (SuPER) method was adapted for the first time to a fungal study to determine the entire fungal community of fungal combs and to test whether fungi other than the symbiotic cultivar interact with termite hosts. Our molecular analyses show that although active combs are dominated by Termitomyces fungi isolated with direct Polymerase Endonuclease Restriction - Denaturing Gradient Gel Electrophoresis (PCR-DGGE), they can also harbor some filamentous fungi and yeasts only revealed by SuPER PCR-DGGE. This is the first molecular evidence of the presence of non-Termitomyces species in active combs. However, because there is no evidence for a species-specific relationship between these fungi and termites, they are mere transient guests with no specialization in the symbiosis. It is however surprising to notice that termite-associated Xylaria strains were not isolated from active combs even though they are frequently retrieved when nests are abandoned by termites. This finding highlights the implication of fungus-growing termites in the regulation of fungi occurring within the combs and also suggests that they might not have any particular evolutionary-based association with Xylaria species.

Molecular and morphological evidence for the delimitation of Xylaria hypoxylon

Xylaria hypoxylon, the type species of Xylaria (Xylariaceae, Sordariomycetes), was first described by Linnaeus as Clavaria hypoxylon from Sweden. Saccardo and other mycologists assumed a cosmopolitan distribution for this species. However, contradictory reports in the literature on its morphoanatomical characters and strongly inconsistent rDNA sequence data attributed to this species in GenBank suggested the existence of an unresolved species complex. To address this lack of clarity, molecular and morphological characters of numerous specimens and corresponding cultures of X. hypoxylon and related taxa from Europe were studied. Newly obtained 5.8S/ITS nrDNA sequence data were compared with published data and sequences of reference strains. European populations of X. hypoxylon from various hosts exhibited consistent rDNA sequence data and a relatively uniform holomorphic morphology, except for one specimen from Sweden that deviated in its ascospore morphology. Some samples from western United States showed DNA sequence data being identical to those of specimens from Europe, confirming a North American occurrence of X. hypoxylon. DNA sequences and morphology of other extra-European material however showed substantial deviations. Definitely not conspecific with the European material examined in this study is a strain, assigned to X. hypoxylon, the DNA sequence data of which have been used in various phylogenetic studies as a representative of Xylariaceae and Xylariales respectively. This material probably represents X longiana.