Actinomycetes inhibit filamentous fungi from the cuticle of Acromyrmex leafcutter ants

Gut flora alterations among aquatic firefly Aquatica leii inhabiting various dissolved oxygen in fresh water

Knowledge about the impact of different dissolved oxygen (DO) on the composition and function of gut bacteria of aquatic insects is largely unknown. Herein, we constructed freshwater environments with different DOs (hypoxia: 2.50 ± 0.50, normoxia: 7.00 ± 0.50, and hyperoxia: 13.00 ± 0.50 mg/L) where aquatic firefly Aquatica leii larvae lived for three months. Their gut flora was analyzed using the combination of 16S rRNA amplicon sequencing and metagenomics. The results showed no difference in alpha diversity of the gut flora between A. leii inhabiting various DOs. However, the relative abundance of several bacterial lineages presented significant changes, such as Pseudomonas. In addition, bacterial genes with an altered relative abundance in response to various DOs were primarily related to metabolism. The alteration of these functions correlated with the DO change. This is the first to uncover structure of gut flora under various DOs in aquatic insect larvae.

Symbiotic Bacteria Regulating Insect-Insect/Fungus/Virus Mutualism

Bacteria associated with insects potentially provide many beneficial services and have been well documented. Mutualism that relates to insects is widespread in ecosystems. However, the interrelation between "symbiotic bacteria" and "mutualism" has rarely been studied. We introduce three systems of mutualism that relate to insects (ants and honeydew-producing Hemiptera, fungus-growing insects and fungi, and plant persistent viruses and vector insects) and review the species of symbiotic bacteria in host insects, as well as their functions in host insects and the mechanisms underlying mutualism regulation. A deeper understanding of the molecular mechanisms and role of symbiotic bacteria, based on metagenomics, transcriptomics, proteomics, metabolomics, and microbiology, will be required for describing the entire interaction network.

Anti-Insect Properties of Penicillium Secondary Metabolites

In connection with their widespread occurrence in diverse environments and ecosystems, fungi in the genus Penicillium are commonly found in association with insects. In addition to some cases possibly implying a mutualistic relationship, this symbiotic interaction has mainly been investigated to verify the entomopathogenic potential in light of its possible exploitation in ecofriendly strategies for pest control. This perspective relies on the assumption that entomopathogenicity is often mediated by fungal products and that Penicillium species are renowned producers of bioactive secondary metabolites. Indeed, a remarkable number of new compounds have been identified and characterized from these fungi in past decades, the properties and possible applications of which in insect pest management are reviewed in this paper.

Soil actinobacteria inhibit antagonistic fungi of leafcutter ant colonies

Founder females of the leaf-cutting ant species Atta sexdens experience high mortality during the founding and establishment of their colonies. The foundation site is crucial for the success of a new colony. In this study, we isolated and identified actinobacteria from fungus garden chambers of A. sexdens colony growth in soils from (1) forested areas without leafcutter ant nests and (2) open ground areas close to leafcutter ant nests. The inhibitory effect of these isolates on pathogenic fungi and the mutualistic fungus cultivated by leafcutter ants was evaluated. The 16S rRNA gene sequences were employed to identify nine selected actinobacteria species found in the soil: Streptomyces (6), Nocardia (2), and Kitasatospora (1). One Streptomyces and one Kitasatospora isolate inhibited all the tested fungi. Since there is no evidence of actinobacteria cultivation in the workers' cuticle of the Atta genus, our results corroborate the hypothesis that these workers may establish temporary adaptive symbiosis with soil microorganisms that produce antibiotic substances, living in some parts of their nest, or even inside their bodies. Pathogenic fungi are a risk factor that can be controlled by actinobacteria metabolites from soils, with minimal energy cost to the colony.

Low Virulence of the Fungi Escovopsis and Escovopsioides to a Leaf-Cutting Ant-Fungus Symbiosis

Eusocial insects interact with a diversity of parasites that can threaten their survival and reproduction. The amount of harm these parasites cause to their hosts (i.e., their virulence) can be influenced by numerous factors, such as the ecological context in which the parasite and its host are inserted. Leaf-cutting ants (genera Atta, Acromyrmex and Amoimyrmex, Attini: Formicidae) are an example of a eusocial insect whose colonies are constantly threatened by parasites. The fungi Escovopsis and Escovopsioides (Ascomycota: Hypocreales) are considered a highly virulent parasite and an antagonist, respectively, to the leaf-cutting ants' fungal cultivar, Leucoagaricus gongylophorus (Basidiomycota: Agaricales). Since Escovopsis and Escovopsioides are common inhabitants of healthy colonies that can live for years, we expect them to have low levels of virulence. However, this virulence could vary depending on ecological context. We therefore tested two hypotheses: (i) Escovopsis and Escovopsioides are of low virulence to colonies; (ii) virulence increases as colony complexity decreases. For this, we used three levels of complexity: queenright colonies (fungus garden with queen and workers), queenless colonies (fungus garden and workers, without queen) and fungus gardens (without any ants). Each was inoculated with extremely high concentrations of conidia of Escovopsis moelleri, Escovopsioides nivea, the mycoparasitic fungus Trichoderma longibrachiatum or a blank control. We found that these fungi were of low virulence to queenright colonies. The survival of queenless colonies was decreased by E. moelleri and fungus gardens were suppressed by all treatments. Moreover, E. nivea and T. longibrachiatum seemed to be less aggressive than E. moelleri, observed both in vivo and in vitro. The results highlight the importance of each element (queen, workers and fungus garden) in the leaf-cutting ant-fungus symbiosis. Most importantly, we showed that Escovopsis may not be virulent to healthy colonies, despite commonly being described as such, with the reported virulence of Escovopsis being due to poor colony conditions in the field or in laboratory experiments.

Host Susceptibility Modulates Escovopsis Pathogenic Potential in the Fungiculture of Higher Attine Ants

Health and disease emerge from intricate interactions between genotypes, phenotypes, and environmental features. The outcomes of such interactions are context-dependent, existing as a dynamic continuum ranging from benefits to damage. In host-microbial interactions, both the host and environmental conditions modulate the pathogenic potential of a microorganism. Microbial interactions are the core of the agricultural systems of ants in the subtribe Attina, which cultivate basidiomycete fungi for food. The fungiculture environment harbors a diverse microbial community, including fungi in the genus Escovopsis that has been studied as damage-causing agent. Here, we consider the ant colony as a host and investigate to what extent its health impacts the dynamics and outcomes of host-Escovopsis interactions. We found that different ant fungal cultivars vary in susceptibility to the same Escovopsis strains in plate-assays interactions. In subcolony-Escovopsis interactions, while healthy subcolonies gradually recover from infection with different concentrations of Escovopsis conidia, insecticide-treated subcolonies evidenced traits of infection and died within 7 days. The opportunistic nature of Escovopsis infections indicates that diseases in attine fungiculture are a consequence of host susceptibility, rather than the effect of a single microbial agent. By addressing the host susceptibility as a major modulator of Escovopsis pathogenesis, our findings expand the understanding of disease dynamics within attine colonies.

Pseudonocardia Symbionts of Fungus-Growing Ants and the Evolution of Defensive Secondary Metabolism

Actinobacteria belonging to the genus Pseudonocardia have evolved a close relationship with multiple species of fungus-growing ants, where these bacteria produce diverse secondary metabolites that protect the ants and their fungal mutualists from disease. Recent research has charted the phylogenetic diversity of this symbiosis, revealing multiple instances where the ants and Pseudonocardia have formed stable relationships in which these bacteria are housed on specific regions of the ant's cuticle. Parallel chemical and genomic analyses have also revealed that symbiotic Pseudonocardia produce diverse secondary metabolites with antifungal and antibacterial bioactivities, and highlighted the importance of plasmid recombination and horizontal gene transfer for maintaining these symbiotic traits. Here, we propose a multi-level model for the evolution of Pseudonocardia and their secondary metabolites that includes symbiont transmission within and between ant colonies, and the potentially independent movement and diversification of their secondary metabolite biosynthetic genes. Because of their well-studied ecology and experimental tractability, Pseudonocardia symbionts of fungus-growing ants are an especially useful model system to understand the evolution of secondary metabolites, and also comprise a significant source of novel antibiotic and antifungal agents.

Cornifronone: A cadinane-type sesquiterpene from a mason bee (Osmia cornifrons)–derived Streptomyces sp

A new cadinane-type sesquiterpene named cornifronone is isolated from the body surface of a mason bee ( Osmia cornifrons)–derived Streptomyces sp. OC1611-8A. Its structure is identified by high-resolution electrospray ionization mass spectrometry data and nuclear magnetic resonance spectroscopic analysis. The absolute configuration of cornifronone was determined by electronic circular dichroism spectra calculations. Cornifronone inhibits hexokinase activity with a mean IC50 of 124.3 μM.

Streptomyces amphotericinicus sp. nov., an amphotericin-producing actinomycete isolated from the head of an ant (Camponotus japonicus Mayr)

A novel actinomycete, designated strain 1H-SSA8^T, was isolated from the head of an ant (Camponotus japonicus Mayr) and was found to produce amphotericin. A polyphasic approach was employed to determine the status of strain 1H-SSA8^T. Morphological and chemotaxonomic characteristics were consistent with those of members of the genus Streptomyces. The menaquinones detected were MK-9(H6), MK-9(H8) and MK-9(H4). The phospholipid profile consisted of diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine and phosphatidylinositol mannoside. The major fatty acids were identified as iso-C16 : 0, C16 : 0, C15 : 0 and anteiso-C15 : 0. Analysis of the 16S rRNA gene sequence showed that strain 1H-SSA8^T belongs to the genus Streptomyces with high sequence similarity to Streptomyces ramulosus NRRL B-2714^T (99.2 %). Two tree-making algorithms based on 16S rRNA gene sequences showed that the isolate formed a phyletic line with Streptomyces himastatinicus ATCC 53653^T (98.7 %). The MLSA utilizing partial sequences of the housekeeping genes (atpD, gyrB, recA, rpoB and trpB) also supported the position. However, evolutionary distances were higher than the 0.007 MLSA evolutionary distance threshold proposed for species-level relatedness. Moreover, the low level of DNA-DNA relatedness and phenotypic differences allowed the novel isolate to be differentiated from its most closely related strain S. ramulosus NRRL B-2714^T and strain S. himastatinicus ATCC 53653^T. It is concluded that the organism can be classified as representing a novel species of the genus Streptomyces, for which the name Streptomyces amphotericinicus sp. nov. is proposed. The type strain is 1H-SSA8^T (=CGMCC 4.7350^T=DSM 103128^T).

Molecules to Ecosystems: Actinomycete Natural Products In situ

Actinomycetes, filamentous actinobacteria found in numerous ecosystems around the globe, produce a wide range of clinically useful natural products (NP). In natural environments, actinomycetes live in dynamic communities where environmental cues and ecological interactions likely influence NP biosynthesis. Our current understating of these cues, and the ecological roles of NP, is in its infancy. We postulate that understanding the ecological context in which actinomycete metabolites are made is fundamental to advancing the discovery of novel NP. In this review we explore the ecological relevance of actinomycetes and their secondary metabolites from varying ecosystems, and suggest that investigating the ecology of actinomycete interactions warrants particular attention with respect to metabolite discovery. Furthermore, we focus on the chemical ecology and in situ analysis of actinomycete NP and consider the implications for NP biosynthesis at ecosystem scales.

Autochthonous microbial community associated with pine needle forest litterfall influences its degradation under natural environmental conditions

The slow natural degradation of chir pine (Pinus roxburghii) needle litterfall and its accumulation on forest floors have been attributed to its lignocellulosic complexities of the biomass. The present study offers a microbiological insight into the role of autochthonous microflora associated with pine needle litterfall in its natural degradation. The denaturing gradient gel electrophoresis (DGGE) fingerprinting indicated actinomycetes (Saccharomonospora sp., Glycomyces sp., Agrococcus sp., Leifsonia sp., Blastocatella sp., and Microbacterium sp.) as a dominant microbial community associated with pine needle litterfall with the absence of fungal decomposers. On exclusion of associated autochthonous microflora from pine litterfall resulted in colonization by decomposer fungi identified as Penicillium chrysogenum and Aspergillus sp., which otherwise failed to colonize the litterfall under natural conditions. The results, therefore, indicated that the autochthonous microbial community of pine needle litterfall (dominated by actinomycetes) obstructs the colonization of litter-degrading fungi and subsequently hinders the overall process of natural degradation of litterfall.