The application of entomopathogenic nematode modified microbial communities within nesting mounds of the red imported fire ants, Solenopsis invicta

Entomopathogenic microorganisms (e.g., fungi, bacteria, nematodes) have been widely used in biological control of soil-dwelling pests, including the red imported fire ant (RIFA), Solenopsis invicta, a notorious invasive pest worldwide. The application of large amounts of entomopathogenic microorganisms to soil may affect the indigenous soil microbial communities. However, reports about the effect of entomopathogenic nematodes (EPN) on soil microbial communities are very few. In this study, the effects of EPN on RIFA populations and microbial communities in mounds were investigated. Our results showed that the application of the EPN Steinernema carpocapsae. All strain on mounds efficaciously suppressed RIFA worker populations, without forming significantly more satellite mounds compared with the control treatment. The application of EPN did not impact the bacterial and fungal diversity in soils derived from the RIFA mounds. However, it slightly altered the taxonomic make-up of the bacterial communities, but significantly altered the taxonomic composition of fungal communities at the phylum, family, and genus levels. The abundances of some beneficial bacteria and fungi, such as Streptomyces, decreased, while those of plant and animal pathogenic bacteria and fungi, dramatically increased, after EPN treatment. On the other hand, the abundances of some entomopathogenic fungi, such as Fusicolla, Clonostachys, and Mortierella, increased. Redundancy analysis or canonical correspondence analysis revealed a positive correlation between the efficacious EPN control and the presence of the insect-resistant bacteria, Sinomonas, as well as entomopathogenic fungi Fusicolla and Mortierella. This suggests that the interactions between EPN and entomopathogenic fungi may play a role in the biological control of RIFA. Our discoveries shed light on the interactions among EPN, RIFA, and soil microbial communities, and emphasize a possible mutualistic relationship between EPN and entomopathogenic fungi in the biological control of RIFA.

The bacterial and fungal community composition in time and space in the nest mounds of the ant Formica exsecta (Hymenoptera: Formicidae)

In a subarctic climate, the seasonal shifts in temperature, precipitation, and plant cover drive the temporal changes in the microbial communities in the topsoil, forcing soil microbes to adapt or decline. Many organisms, such as mound-building ants, survive the cold winter owing to the favorable microclimate in their nest mounds. We have previously shown that the microbial communities in the nest of the ant Formica exsecta are significantly different from those in the surrounding bulk soil. In the current study, we identified taxa, which were consistently present in the nests over a study period of three years. Some taxa were also significantly enriched in the nest samples compared with spatially corresponding reference soils. We show that the bacterial communities in ant nests are temporally stable across years, whereas the fungal communities show greater variation. It seems that the activities of the ants contribute to unique biochemical processes in the secluded nest environment, and create opportunities for symbiotic interactions between the ants and the microbes. Over time, the microbial communities may come to diverge, due to drift and selection, especially given the long lifespan (up to 30 years) of the ant colonies.

The bacterial and fungal nest microbiomes in populations of the social spider Stegodyphus dumicola

Social spiders of the species Stegodyphus dumicola live in communal nests with hundreds of individuals and are characterized by extremely low species-wide genetic diversity. The lack of genetic diversity in combination with group living imposes a potential threat for infection by pathogens. We therefore proposed that specific microbial symbionts inhabiting the spider nests may provide antimicrobial defense. To compare the bacterial and fungal diversity in 17 nests from three different locations in Namibia, we used 16S rRNA gene and internal transcribed spacer (ITS2) sequencing. The nest microbiomes differed between geographically distinct spider populations and appeared largely determined by the local environment. Nevertheless, we identified a core microbiome consisting of four bacterial genera (Curtobacterium, Modestobacter, Sphingomonas, Massilia) and four fungal genera (Aureobasidium, Didymella, Alternaria, Ascochyta), which likely are selected from surrounding soil and plants by the nest environment. We did not find indications for a strain- or species-specific symbiosis in the nests. Isolation of bacteria and fungi from nest material retrieved a few bacterial strains with antimicrobial activity but a number of antimicrobial fungi, including members of the fungal core microbiome. The significance of antimicrobial taxa in the nest microbiome for host protection remains to be shown.

Chance or Necessity-The Fungi Co-Occurring with Formica polyctena Ants

Simple Summary

There are about 13,800 species of ants living around the world, but only some of them have been extensively studied in the context of their non−antagonistic relationships with fungi. The best−known example is the symbiosis between leaf−cutting ants and fungi serving them as food. Others include the relationship between ants living in carton nests in the trees’ canopy with fungi increasing the durability of the nest. Do ants utilize fungi in the northern hemisphere and cooler climatic zone? This question is still open. Our goal was to study the less−obvious interactions between ants and common fungi in temperate climates. In our study, we characterized the mycobiota of the surroundings of Formica polyctena ants. We identified nearly 600 strains and investigated their taxonomic affinity. The most abundant fungi in F. polyctena nests are strains belonging to Penicillium—a genus well−known as an antibiotic producer. Other common and widespread fungi related to Penicillium, such as the toxin−producing Aspergillus species, were isolated very rarely. Additionally, the high diversity and high frequency of Penicillium colonies isolated from ants in this study suggest that certain representatives of this genus may be adapted to survive in ant nests, or that they are preferentially sustained by the insects.

Abstract

Studies on carton nesting ants and domatia−dwelling ants have shown that ant–fungi interactions may be much more common and widespread than previously thought. Until now, studies focused predominantly on parasitic and mutualistic fungi–ant interactions occurring mostly in the tropics, neglecting less−obvious interactions involving the fungi common in ants’ surroundings in temperate climates. In our study, we characterized the mycobiota of the surroundings of Formica polyctena ants by identifying nearly 600 fungal colonies that were isolated externally from the bodies of F. polyctena workers. The ants were collected from mounds found in northern and central Poland. Isolated fungi were assigned to 20 genera via molecular identification (ITS rDNA barcoding). Among these, Penicillium strains were the most frequent, belonging to eight different taxonomic sections. Other common and widespread members of Eurotiales, such as Aspergillus spp., were isolated very rarely. In our study, we managed to characterize the genera of fungi commonly present on F. polyctena workers. Our results suggest that Penicillium, Trichoderma, Mucor, Schwanniomyces and Entomortierella are commonly present in F. polyctena surroundings. Additionally, the high diversity and high frequency of Penicillium colonies isolated from ants in this study suggest that representatives of this genus may be adapted to survive in ant nests environment better than the other fungal groups, or that they are preferentially sustained by the insects in nests.

Do Host Plant and Associated Ant Species Affect Microbial Communities in Myrmecophytes?

Ant-associated microorganisms can play crucial and often overlooked roles, and given the diversity of interactions that ants have developed, the study of the associated microbiomes is of interest. We focused here on specialist plant-ant species of the genus Allomerus that grow a fungus to build galleries on their host-plant stems. Allomerus-inhabited domatia, thus, might be a rich arena for microbes associated with the ants, the plant, and the fungus. We investigated the microbial communities present in domatia colonised by four arboreal ants: Allomerus decemarticulatus, A. octoarticulatus, A. octoarticulatus var. demerarae, and the non-fungus growing plant-ant Azteca sp. cf. depilis, inhabiting Hirtella physophora or Cordia nodosa in French Guiana. We hypothesized that the microbial community will differ among these species. We isolated microorganisms from five colonies of each species, sequenced the 16S rRNA or Internal TranscribedSpacer (ITS) regions, and described both the alpha and beta diversities. We identified 69 microbial taxa, which belong to five bacterial and two fungal phyla. The most diverse phyla were Proteobacteria and Actinobacteria. The microbial community of Azteca cf. depilis and Allomerus spp. differed in composition and richness. Geographical distance affected microbial communities and richness but plant species did not. Actinobacteria were only associated with Allomerus spp.

Ant colonies promote the diversity of soil microbial communities

Little is known about the role of ant colonies in regulating the distribution and diversity of soil microbial communities across large spatial scales. Here, we conducted a survey across >1000 km in eastern Australia and found that, compared with surrounding bare soils, ant colonies promoted the richness (number of phylotypes) and relative abundance of rare taxa of fungi and bacteria. Ant nests were also an important reservoir for plant pathogens. Our study also provides a portfolio of microbial phylotypes only found in ant nests, and which are associated with high nutrient availability. Together, our work highlights the fact that ant nests are an important refugia for microbial diversity.

Trends in bacterial and fungal communities in ant nests observed with Terminal-Restriction Fragment Length Polymorphism (T-RFLP) and Next Generation Sequencing (NGS) techniques-validity and compatibility in ecological studies

Microbes are ubiquitous and often occur in functionally and taxonomically complex communities. Unveiling these community dynamics is one of the main challenges of microbial research. Combining a robust, cost effective and widely used method such as Terminal Restriction Fragment Length Polymorphism (T-RFLP) with a Next Generation Sequencing (NGS) method (Illumina MiSeq), offers a solid alternative for comprehensive assessment of microbial communities. Here, these two methods were combined in a study of complex bacterial and fungal communities in the nest mounds of the ant Formica exsecta, with the aim to assess the degree to which these methods can be used to complement each other. The results show that these methodologies capture similar spatiotemporal variations, as well as corresponding functional and taxonomical detail, of the microbial communities in a challenging medium consisting of soil, decomposing plant litter and an insect inhabitant. Both methods are suitable for the analysis of complex environmental microbial communities, but when combined, they complement each other well and can provide even more robust results. T-RFLP can be trusted to show similar general community patterns as Illumina MiSeq and remains a good option if resources for NGS methods are lacking.

Transcriptome sequencing reveals high isoform diversity in the ant Formica exsecta

Transcriptome resources for social insects have the potential to provide new insight into polyphenism, i.e., how divergent phenotypes arise from the same genome. Here we present a transcriptome based on paired-end RNA sequencing data for the ant Formica exsecta (Formicidae, Hymenoptera). The RNA sequencing libraries were constructed from samples of several life stages of both sexes and female castes of queens and workers, in order to maximize representation of expressed genes. We first compare the performance of common assembly and scaffolding software (Trinity, Velvet-Oases, and SOAPdenovo-trans), in producing de novo assemblies. Second, we annotate the resulting expressed contigs to the currently published genomes of ants, and other insects, including the honeybee, to filter genes that have annotation evidence of being true genes. Our pipeline resulted in a final assembly of altogether 39,262 mRNA transcripts, with an average coverage of >300X, belonging to 17,496 unique genes with annotation in the related ant species. From these genes, 536 genes were unique to one caste or sex only, highlighting the importance of comprehensive sampling. Our final assembly also showed expression of several splice variants in 6,975 genes, and we show that accounting for splice variants affects the outcome of downstream analyses such as gene ontologies. Our transcriptome provides an outstanding resource for future genetic studies on F. exsecta and other ant species, and the presented transcriptome assembly can be adapted to any non-model species that has genomic resources available from a related taxon.