Symbiotic fungal flora in leaf galls induced by Illiciomyia yukawai (Diptera: Cecidomyiidae) and in its mycangia

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

Mycobiomes of two distinct clades of ambrosia gall midges (Diptera: Cecidomyiidae) are species-specific in larvae but similar in nutritive mycelia

IMPORTANCE

Ambrosia gall midges are endophagous insect herbivores whose larvae live enclosed within a single gall for their entire development period. They may exhibit phytomycetophagy, a remarkable feeding mode that involves the consumption of plant biomass and mycelia of their cultivated gall symbionts. Thus, AGMs are ideal model organisms for studying the role of microorganisms in the evolution of host specificity in insects. However, compared to other fungus-farming insects, insect-fungus mutualism in AGMs has been neglected. Our study is the first to use DNA metabarcoding to characterize the complete mycobiome of the entire system of the gall-forming insects as we profiled gall surfaces, nutritive mycelia, and larvae. Interestingly, larval mycobiomes were significantly different from their nutritive mycelia, although Botryosphaeria dothidea dominated the nutritive mycelia, regardless of the evolutionary separation of the tribes studied. Therefore, we confirmed a long-time hypothesized paradigm for the important evolutionary association of this fungus with AGMs.

Vascular implications of Dasineura sp. galls' establishment on Peumus boldus stems

Some chewing larvae are capable of inducing galls in the host vascular cylinder, e.g. Dasineura sp. (Cecidomyiidae) on Peumus boldus stems. Due to the medicinal and economic importance of P. boldus, the anatomical and functional implications of establishment of Dasineura sp. on P. boldus stems were investigated. We asked if establishment of Dasineura sp. in P. boldus stems induces abnormalities at the cellular and organizational level of the vascular system that increase during gall development in favour of the hydric status of the gall. Anatomical alterations induced in the stems during gall development were determined. Cytohistometric analyses in mature galls were compared to non-galled stems, and water potential and leaf area of non-galled stems were compared with galled stems. Dasineura sp. establishes in the vascular cambium, leading to delignification and rupture of xylem cells, inhibiting formation of phloem and perivascular sclerenchyma. Gall diameter increases together with larval feeding activity, producing a large larval chamber and numerous layers of nutritive tissue, vascular parenchyma, and sclerenchyma. These anatomical alterations do not affect the leaf area of galled stems but favour increased water flow towards these stems. The anatomical alterations induced by Dasineura sp. in P. boldus stems guarantee water and nutrient supply to the gall and larva. After the inducer exits stems, some host branches no longer have vascular connections with the plant body.

An Integrative Study on Asphondylia spp. (Diptera: Cecidomyiidae), Causing Flower Galls on Lamiaceae, with Description, Phenology, and Associated Fungi of Two New Species

An integrative study on some species of Asphondylia was carried out. Two species of gall midges from Italy, Asphondylia rivelloi sp. nov. and Asphondylia micromeriae sp. nov. (Diptera: Cecidomyiidae), causing flower galls respectively on Clinopodium vulgare and Micromeria graeca (Lamiaceae), are described and illustrated. The characteristics of each developmental stage and induced galls are described, which allowed the discrimination of these new species in the complex of Asphondylia developing on Lamiaceae plants. Molecular data based on sequencing both nuclear (ITS2 and 28S-D2) and mitochondrial (COI) genes are also provided in support of this discrimination. Phylogeny based on nuclear markers is consistent with the new species, whereas COI phylogeny suggests introgression occurring between the two species. However, these species can also be easily identified using a morphological approach. Phenology of host plants and gall midges are described, and some peculiar characteristics allow the complete and confident discrimination and revision of the treated species. Gall-associated fungi were identified as Botryosphaeria dothidea,Alternaria spp., and Cladosporium spp.

New Cladosporium Species from Normal and Galled Flowers of Lamiaceae

A series of isolates of Cladosporium spp. were recovered in the course of a cooperative study on galls formed by midges of the genus Asphondylia (Diptera, Cecidomyidae) on several species of Lamiaceae. The finding of these fungi in both normal and galled flowers was taken as an indication that they do not have a definite relationship with the midges. Moreover, identification based on DNA sequencing showed that these isolates are taxonomically heterogeneous and belong to several species which are classified in two different species complexes. Two new species, Cladosporium polonicum and Cladosporium neapolitanum, were characterized within the Cladosporium cladosporioides species complex based on strains from Poland and Italy, respectively. Evidence concerning the possible existence of additional taxa within the collective species C. cladosporioides and C. pseudocladosporioides is discussed.

Ecology and Evolution of Insect-Fungus Mutualisms

The evolution of a mutualism requires reciprocal interactions whereby one species provides a service that the other species cannot perform or performs less efficiently. Services exchanged in insect-fungus mutualisms include nutrition, protection, and dispersal. In ectosymbioses, which are the focus of this review, fungi can be consumed by insects or can degrade plant polymers or defensive compounds, thereby making a substrate available to insects. They can also protect against environmental factors and produce compounds antagonistic to microbial competitors. Insects disperse fungi and can also provide fungal growth substrates and protection. Insect-fungus mutualisms can transition from facultative to obligate, whereby each partner is no longer viable on its own. Obligate dependency has (a) resulted in the evolution of morphological adaptations in insects and fungi, (b) driven the evolution of social behaviors in some groups of insects, and (c) led to the loss of sexuality in some fungal mutualists.

A specific antimicrobial protein CAP-1 from Pseudomonas sp. isolated from the jellyfish Cyanea capillata

A bacterium strain, designated as CMF-2, was isolated from the jellyfish Cyanea capillata and its culture supernatant exhibited a significant antimicrobial activity. The strain CMF-2 was identified as Pseudomonas sp. based on the morphological, biochemical and physiological characteristics as well as 16S rRNA sequence analysis. In this study, an antimicrobial protein, named as CAP-1, was isolated from the culture of CMF-2 through ammonium sulfate precipitation and gel filtration chromatography. According to the result of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a major band indicated that the antimicrobial protein had a molecular mass of about 15 kDa, and it was identified as a hypothetical protein by MALDI-TOF-MS analysis and Mascot searching. CAP-1 displayed a broad antimicrobial spectrum against the indicator bacteria and fungus, including Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Candida albicans, especially some marine-derived microorganisms such as Vibrio vulnificus, Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio cholera, and Vibrio anguillarum, but showed little impact on tumor cells and normal human cells. The protein CAP-1 remained a stable antimicrobial activity in a wide range of temperature (20-80°C) and pH (2-10) conditions. These results suggested that CAP-1 might have a specific antimicrobial function not due to cytotoxicity.

Is a Gall an Extended Phenotype of the Inducing Insect? A Comparative Study of Selected Morphological and Physiological Traits of Leaf and Stem Galls on Machilus thunbergii (Lauraceae) Induced by Five Species of Daphnephila (Diptera: Cecidomyiidae) in Northeastern Taiwan

Mature galls induced by Daphnephila truncicola, D. taiwanensis, D. sueyenae, D. stenocalia, and D. ornithocephala on Machilus thunbergii in northern Taiwan were examined to verify the dictum that the morphology of galls is an expression of the extended phenotype of the respective gall-inducing insect. Based on their length-width ratio, the materials were grouped into either fleshy (those induced by D. taiwanensis and D. sueyenae) or slim galls (those induced by D. truncicola, D. stenocalia, and D. ornithocephala). Stem galls induced by D. truncicola showed an energy level of 0.0178 kJ/g. Among leaf galls, the greatest energy level was in the one induced by D. stenocalia (0.0193 kJ/g), followed by D. sueyenae (0.0192 kJ/g), D. taiwanensis (0.0189 kJ/g), and D. ornithocephala (0.0160 kJ/g). The numbers of reserve and nutritive cell layers in galls were greater in the stem galls induced by D. truncicola, similar to those in the fleshy leaf galls, than in the slim leaf galls. Based on the fungal taxa isolated from the larval chambers and considering the similarities and divergences among gall characteristics, the galls induced by D. truncicola and D. taiwanensis clustered into one, whereas those of D. sueyenae aligned with the 'D. stenocalia-D. ornithocephala' cluster. The present study verified that shapes, structure, nutritive tissues, energy levels, and multiple coexisting fungal taxa within galls reinforce that they are extended phenotypes of the respective gall-inducing Daphnephila species and they represent adaptive evolution of Daphnephila on M. thunbergii.

Immunosuppressive potential of Botryosphaeria dothidea, an endophyte isolated from Kigelia africana

CONTEXT

For years, natural products from microbes have been used as drugs. Endophytes are the most important fungi that produce many novel metabolites for potential use in pharmacology and agriculture.

OBJECTIVE

The objective of the present study was to explore new endophytes for novel natural products.

MATERIALS AND METHODS

An endophyte BAK-I was isolated from the bark of Kigelia africana (Lam.) Beneth (Bignoniaceae). BAK-I was characterized morphologically and on the basis of ITS-5.8S rDNA sequences. BAK-I was fermented to yield an extract, which was evaluated for its anticancer, antimicrobial, and immunomodulatory activities, using MTT, agar well-diffusion, tube dilution method, lymphocyte proliferation, and pro-inflammatory cytokines (TNF-α) (by macrophages) evaluation assays. For lymphocyte proliferation and pro-inflammatory cytokines studies, four concentrations were evaluated 10, 30, 100, and 1000 µg/mL and the experiments were conducted for 72 and 48 h, respectively.

RESULTS AND DISCUSSION

The BAK-I showed pink cottony growth. SEM studies showed smooth fusoid-oblong conidia with a truncated base. Furthermore, ITS-5.8S rDNA sequence showed 99% homology with the Botryosphaeria dothidea strain suggesting that the endophyte is a strain of the genus Botryosphaeria. Less than 50% growth inhibition of SF295, Lung A-549, and THP-1 cancer cell lines after treatment with BAK-I extract suggested that it did not have significant cytotoxic potential, whereas it is bactericidal for Gram-positive pathogens MRSA and VRE with MIC value 200 and 250 µg/mL, respectively. To elucidate its immunomodulation potential, splenocyte proliferation studies showed that BAK-1 suppressed the T cell proliferation by 50%. TNF-α evaluation studies also showed that the extract inhibited TNF-α production in a concentration-dependent manner suggesting that it had immunosuppressive potential. Inhibition at 10 µg/mL was found to be 55% as against 48% using β-methasone.

CONCLUSION

The results suggested that BAK-I extract can be used as a potential immunosuppressive agent.

Microbial symbionts shape the sterol profile of the xylem-feeding woodwasp, Sirex noctilio

The symbiotic fungus Amylostereum areolatum is essential for growth and development of larvae of the invasive woodwasp, Sirex noctilio. In the nutrient poor xylem of pine trees, upon which Sirex feeds, it is unknown whether Amylostereum facilitates survival directly through consumption (mycetophagy) and/or indirectly through digestion of recalcitrant plant polymers (external rumen hypothesis). We tested these alternative hypotheses for Amylostereum involvement in Sirex foraging using the innate dependency of all insects on dietary sources of sterol and the unique sterols indicative of fungi and plants. We tested alternative hypotheses by using GC-MS to quantify concentrations of free and bound sterol pools from multiple life-stages of Sirex, food sources, and waste products in red pine (Pinus resinosa). Cholesterol was the primary sterol found in all life-stages of Sirex. However, cholesterol was not found in significant quantities in either plant or fungal resources. Ergosterol was the most prevalent sterol in Amylostereum but was not detectable in either wood or insect tissue (<0.001 μg/g). Phytosterols were ubiquitous in both pine xylem and Sirex. Therefore, dealkylation of phytosterols (sitosterol and campesterol) is the most likely pathway to meet dietary demand for cholesterol in Sirex. Ergosterol concentrations from fungal-infested wood demonstrated low fungal biomass, which suggests mycetophagy is not the primary source of sterol or bulk nutrition for Sirex. Our findings suggest there is a potentially greater importance for fungal enzymes, including the external digestion of recalcitrant plant polymers (e.g., lignin and cellulose), shaping this insect-fungal symbiosis.

Endophytic fungus-vascular plant-insect interactions

Insect association with fungi has a long history. Theories dealing with the evolution of insect herbivory indicate that insects used microbes including fungi as their principal food materials before flowering plants evolved. Subtlety and the level of intricacy in the interactions between insects and fungi indicate symbiosis as the predominant ecological pattern. The nature of the symbiotic interaction that occurs between two organisms (the insect and the fungus), may be either mutualistic or parasitic, or between these two extremes. However, the triangular relationship involving three organisms, viz., an insect, a fungus, and a vascular plant is a relationship that is more complicated than what can be described as either mutualism or parasitism, and may represent facets of both. Recent research has revealed such a complex relationship in the vertically transmitted type-I endophytes living within agriculturally important grasses and the pestiferous insects that attack them. The intricacy of the association depends on the endophytic fungus-grass association and the insect present. Secondary compounds produced in the endophytic fungus-grass association can provide grasses with resistance to herbivores resulting in mutualistic relationship between the fungus and the plant that has negative consequences for herbivorous insects. The horizontally transmitted nongrass type-II endophytes are far less well studied and as such their ecological roles are not fully understood. This forum article explores the intricacy of dependence in such complex triangular relationships drawing from well-established examples from the fungi that live as endophytes in vascular plants and how they impact on the biology and evolution of free-living as well as concealed (e.g., gall-inducing, gall-inhabiting) insects. Recent developments with the inoculation of strains of type-I fungal endophytes into grasses and their commercialization are discussed, along with the possible roles the endophytic fungi play in the galls induced by the Cecidomyiidae (Diptera).