Microbial Communities of the Gut and Nest of the Humus- and Litter-Feeding Termite Procornitermes araujoi (Syntermitinae)

Termite-engineered microbial communities of termite nest structures: a new dimension to the extended phenotype

Termites are a prototypical example of the 'extended phenotype' given their ability to shape their environments by constructing complex nesting structures and cultivating fungus gardens. Such engineered structures provide termites with stable, protected habitats, and nutritious food sources, respectively. Recent studies have suggested that these termite-engineered structures harbour Actinobacteria-dominated microbial communities. In this review, we describe the composition, activities, and consequences of microbial communities associated with termite mounds, other nests, and fungus gardens. Culture-dependent and culture-independent studies indicate that these structures each harbour specialized microbial communities distinct from those in termite guts and surrounding soils. Termites select microbial communities in these structures through various means: opportunistic recruitment from surrounding soils; controlling physicochemical properties of nesting structures; excreting hydrogen, methane, and other gases as bacterial energy sources; and pretreating lignocellulose to facilitate fungal cultivation in gardens. These engineered communities potentially benefit termites by producing antimicrobial compounds, facilitating lignocellulose digestion, and enhancing energetic efficiency of the termite 'metaorganism'. Moreover, mound-associated communities have been shown to be globally significant in controlling emissions of methane and enhancing agricultural fertility. Altogether, these considerations suggest that the microbiomes selected by some animals extend much beyond their bodies, providing a new dimension to the 'extended phenotype'.

Lessons From Insect Fungiculture: From Microbial Ecology to Plastics Degradation

Anthropogenic activities have extensively transformed the biosphere by extracting and disposing of resources, crossing boundaries of planetary threat while causing a global crisis of waste overload. Despite fundamental differences regarding structure and recalcitrance, lignocellulose and plastic polymers share physical-chemical properties to some extent, that include carbon skeletons with similar chemical bonds, hydrophobic properties, amorphous and crystalline regions. Microbial strategies for metabolizing recalcitrant polymers have been selected and optimized through evolution, thus understanding natural processes for lignocellulose modification could aid the challenge of dealing with the recalcitrant human-made polymers spread worldwide. We propose to look for inspiration in the charismatic fungal-growing insects to understand multipartite degradation of plant polymers. Independently evolved in diverse insect lineages, fungiculture embraces passive or active fungal cultivation for food, protection, and structural purposes. We consider there is much to learn from these symbioses, in special from the community-level degradation of recalcitrant biomass and defensive metabolites. Microbial plant-degrading systems at the core of insect fungicultures could be promising candidates for degrading synthetic plastics. Here, we first compare the degradation of lignocellulose and plastic polymers, with emphasis in the overlapping microbial players and enzymatic activities between these processes. Second, we review the literature on diverse insect fungiculture systems, focusing on features that, while supporting insects' ecology and evolution, could also be applied in biotechnological processes. Third, taking lessons from these microbial communities, we suggest multidisciplinary strategies to identify microbial degraders, degrading enzymes and pathways, as well as microbial interactions and interdependencies. Spanning from multiomics to spectroscopy, microscopy, stable isotopes probing, enrichment microcosmos, and synthetic communities, these strategies would allow for a systemic understanding of the fungiculture ecology, driving to application possibilities. Detailing how the metabolic landscape is entangled to achieve ecological success could inspire sustainable efforts for mitigating the current environmental crisis.

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.

Termite gas emissions select for hydrogenotrophic microbial communities in termite mounds

Organoheterotrophs are the dominant bacteria in most soils worldwide. While many of these bacteria can subsist on atmospheric hydrogen (H₂), levels of this gas are generally insufficient to sustain hydrogenotrophic growth. In contrast, bacteria residing within soil-derived termite mounds are exposed to high fluxes of H₂ due to fermentative production within termite guts. Here, we show through community, metagenomic, and biogeochemical profiling that termite emissions select for a community dominated by diverse hydrogenotrophic Actinobacteriota and Dormibacterota. Based on metagenomic short reads and derived genomes, uptake hydrogenase and chemosynthetic RuBisCO genes were significantly enriched in mounds compared to surrounding soils. In situ and ex situ measurements confirmed that high- and low-affinity H₂-oxidizing bacteria were highly active in the mounds, such that they efficiently consumed all termite-derived H₂ emissions and served as net sinks of atmospheric H₂ Concordant findings were observed across the mounds of three different Australian termite species, with termite activity strongly predicting H₂ oxidation rates (R ² = 0.82). Cell-specific power calculations confirmed the potential for hydrogenotrophic growth in the mounds with most termite activity. In contrast, while methane is produced at similar rates to H₂ by termites, mounds contained few methanotrophs and were net sources of methane. Altogether, these findings provide further evidence of a highly responsive terrestrial sink for H₂ but not methane and suggest H₂ availability shapes composition and activity of microbial communities. They also reveal a unique arthropod-bacteria interaction dependent on H₂ transfer between host-associated and free-living microbial communities.

Complementary Contribution of Fungi and Bacteria to Lignocellulose Digestion in the Food Stored by a Neotropical Higher Termite

Lignocellulose digestion in termites is achieved through the functional synergy between gut symbionts and host enzymes. However, some species have evolved additional associations with nest microorganisms that collaborate in the decomposition of plant biomass. In a previous study, we determined that plant material packed with feces inside the nests of Cornitermes cumulans (Syntermitinae) harbors a distinct microbial assemblage. These food nodules also showed a high hemicellulolytic activity, possibly acting as an external place for complementary lignocellulose digestion. In this study, we used a combination of ITS sequence analysis, metagenomics, and metatranscriptomics to investigate the presence and differential expression of genes coding for carbohydrate-active enzymes (CAZy) in the food nodules and the gut of workers and soldiers. Our results confirm that food nodules express a distinct set of CAZy genes suggesting that stored plant material is initially decomposed by enzymes that target the lignin and complex polysaccharides from fungi and bacteria before the passage through the gut, where it is further targeted by a complementary set of cellulases, xylanases, and esterases produced by the gut microbiota and the termite host. We also showed that the expression of CAZy transcripts associated to endoglucanases and xylanases was higher in the gut of termites than in the food nodules. An additional finding in this study was the presence of fungi in the termite gut that expressed CAZy genes. This study highlights the importance of externalization of digestion by nest microbes and provides new evidence of complementary digestion in the context of higher termite evolution.

Supergroup F Wolbachia in terrestrial isopods: Horizontal transmission from termites?

Horizontal transmission between distantly related species has been used to explain how Wolbachia infect multiple species at astonishing rates despite the selection for resistance. Recently, a terrestrial isopod species was found to be infected by an unusual strain of supergroup F Wolbachia. However, only Wolbachia of supergroup B is typically found in isopods. One possibility is that these isopods acquired the infection because of their recurrent contact with termites—a group with strong evidence of infection by supergroup F Wolbachia. Thus, our goals were: (1) check if the infection was an isolated case in isopods, or if it revealed a broader pattern; (2) search for Wolbachia infection in the termites within Brazil; and (3) look for evidence consistent with horizontal transmission between isopods and termites. We collected Neotroponiscus terrestrial isopods and termites along the Brazilian coastal Atlantic forest. We sequenced and identified the Wolbachia strains found in these groups using coxA, dnaA, and fpbA genes. We constructed phylogenies for both bacteria and host taxa and tested for coevolution. We found the supergroup F Wolbachia in other species and populations of Neotroponiscus, and also in Nasutitermes and Procornitermes termites. The phylogenies showed that, despite the phylogenetic distance between isopods and termites, the Wolbachia strains clustered together. Furthermore, cophylogenetic analyses showed significant jumps of Wolbachia between terrestrial isopods and termites. Thus, our study suggests that the horizontal transmission of supergroup F Wolbachia between termites and terrestrial isopods is likely. Our study also helps understanding the success and worldwide distribution of this symbiont.

Insects' potential: Understanding the functional role of their gut microbiome

The study of insect-associated microbial communities is a field of great importance in agriculture, principally because of the role insects play as pests. In addition, there is a recent focus on the potential of the insect gut microbiome in areas such as biotechnology, given some microorganisms produce molecules with biotechnological and industrial applications, and also in biomedicine, since some bacteria and fungi are a reservoir of antibiotic resistance genes (ARGs). To date, most studies aiming to characterize the role of the gut microbiome of insects have been based on high-throughput sequencing of the 16S rRNA gene and/or metagenomics. However, recently functional approaches such as metatranscriptomics, metaproteomics and metabolomics have also been employed. Besides providing knowledge about the taxonomic distribution of microbial populations, these techniques also reveal their functional and metabolic capabilities. This information is essential to gain a better understanding of the role played by microbes comprising the microbial communities in their hosts, as well as to indicate their possible exploitation. This review provides an overview of how far we have come in characterizing insect gut functionality through omics, as well as the challenges and future perspectives in this field.

Seasonal Variations in Soil Microbiota Profile of Termite (Syntermes wheeleri) Mounds in the Brazilian Tropical Savanna

Eusocial animals, such as the termites, often build a nest-like structure called a mound that provides shelter with stable internal conditions and protection against predators. Termites are important components of the Brazilian Cerrado biota. This study aimed to investigate the bacterial community composition and diversity of the Syntermes wheeleri termite-mound soil using culture-independent approaches. We considered the vertical profile by comparing two different mound depths (mound surface and 60 cm) and seasonality with samplings during the rainy and dry seasons. We compared the mound soil microbiota to the adjacent soil without the influence of the mound to test the hypothesis that the Cerrado soil bacterial community was more diverse and more susceptible to seasonality than the mound soil microbiota. The results support the hypothesis that the Cerrado soil bacterial community is more diverse than the mound soil and also has a higher variability among seasons. The number of observed OTUs (Operational Taxonomic Units) was used to express bacterial richness, and it indicates that soil moisture has an effect on the community distribution and richness of the Cerrado samples in comparison to mound samples, which remain stable across seasons. This could be a consequence of the protective role of the mound for the termite colony. The overall community taxonomic profile was similar between soil samples, especially when compared to the taxonomic composition of the Syntermes wheeleri termite's gut, which might be explained by the different characteristics and functionality between the soil and the gut microbial community.

A Natural High-Sugar Diet Has Different Effects on the Prokaryotic Community Structures of Lower and Higher Termites (Blattaria)

The lignocellulosic digestive symbiosis in termites is a dynamic survival adaptation system. While the contribution of hereditary and habitat factors to the development of the symbiotic bacterial community of termites had been confirmed, the manner in which these factors affect functional synergism among different bacterial lineages has still not been fully elucidated. Therefore, the 16S rRNA gene libraries of Odontotermes formosanus Shiraki (Blattodea: Termitidae) and Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae) sampled from sugarcane fields (high sugar) or pine tree forests (no free sugar) were sequenced. The results verify that the prokaryotic community structures of termites could be significantly reshaped by native dietary isolation within a species. Although the most dominant phyla are convergent in all samples, their relative abundances in these two termite species exhibited a reverse variation pattern when the termite hosts were fed on the high-sugar diet. Furthermore, we showed that the taxonomic composition of the dominant phyla at the family or genus level differentiate depending on the diet and the host phylogeny. We hypothesize that the flexible bacterial assemblages at low taxonomic level might exert variable functional collaboration to accommodate to high-sugar diet. In addition, the functional predictions of Tax4Fun suggest a stable metabolic functional structure of the microbial communities of the termites in both different diet habitats and taxonomy. We propose that the symbiotic bacterial community in different host termites developed a different functional synergistic pattern, which may be essential to maintain the stability of the overall metabolic function for the survival of termites.

Phylogenomic analysis of 589 metagenome-assembled genomes encompassing all major prokaryotic lineages from the gut of higher termites

"Higher" termites have been able to colonize all tropical and subtropical regions because of their ability to digest lignocellulose with the aid of their prokaryotic gut microbiota. Over the last decade, numerous studies based on 16S rRNA gene amplicon libraries have largely described both the taxonomy and structure of the prokaryotic communities associated with termite guts. Host diet and microenvironmental conditions have emerged as the main factors structuring the microbial assemblages in the different gut compartments. Additionally, these molecular inventories have revealed the existence of termite-specific clusters that indicate coevolutionary processes in numerous prokaryotic lineages. However, for lack of representative isolates, the functional role of most lineages remains unclear. We reconstructed 589 metagenome-assembled genomes (MAGs) from the different gut compartments of eight higher termite species that encompass 17 prokaryotic phyla. By iteratively building genome trees for each clade, we significantly improved the initial automated assignment, frequently up to the genus level. We recovered MAGs from most of the termite-specific clusters in the radiation of, for example, Planctomycetes, Fibrobacteres, Bacteroidetes, Euryarchaeota, Bathyarchaeota, Spirochaetes, Saccharibacteria, and Firmicutes, which to date contained only few or no representative genomes. Moreover, the MAGs included abundant members of the termite gut microbiota. This dataset represents the largest genomic resource for arthropod-associated microorganisms available to date and contributes substantially to populating the tree of life. More importantly, it provides a backbone for studying the metabolic potential of the termite gut microbiota, including the key members involved in carbon and nitrogen biogeochemical cycles, and important clues that may help cultivating representatives of these understudied clades.

Characterization of mineral phosphate solubilizing and plant growth promoting bacteria from termite soil of arid region

Five highly efficient phosphate solubilizing bacteria, viz., Pantoea sp. A3, Pantoea sp. A34, Kosakonia sp. A37, Kosakonia sp. B7 and Bacillus sp. AH9 were isolated from termitorial soils of Sanjivani island of southern Maharashtra, India. These isolates were characterized and explored for phosphate solubilization and plant growth promotion. Among these, Bacillus sp. AH9 showed highest phosphate solubilization index (3.5) and solubilization efficiency (250%) on Pikovskaya agar. Interestingly, Pantoea sp. A34 displayed maximum mineral phosphate solubilization (1072.35 mg/L) in liquid medium and during this period the pH dropped to 3.13. All five isolates had highest P solubilization at 48 h after inoculation. During mineral phosphate solubilization, both gluconic acid and 2-keto gluconic acid were produced by Kosakonia and Bacillus isolates, while only 2-keto gluconic acid was detected in Pantoea isolates. Highest organic acid (39.07 ± 0.04 g/L) production was envisaged in Bacillus sp. AH9, while Pantoea sp. A34 produced the least amount (13.00 ± 0.01 g/L) of organic acid. Seed bacterization with Pantoea sp. A3 and Kosakonia sp. A37 resulted in ~ 37% and ~ 53% increase in root length of tomato seedlings, respectively, while Pantoea sp. A34 and Kosakonia sp. B7 had deleterious effects on root length as well as overall growth of the seedlings. To our knowledge, this is the first report of plant growth promoting potential of microorganisms isolated from termitorial soil of Sanjivani island, which is a drought-prone area. Therefore, such efficient growth promoting P solubilizers can offer an effective solution for sustainable agriculture in arid, dryland farming and drought-prone regions.