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Correlative imaging by transmission electron microscopy (TEM) and NanoSIMS-50 of a 13 CO2 labelled Allium cepa root colonized with Gigaspora margarita. (a) 12 C 14 N. (b) 13 C/ 12 C × 100 (r13C). (c) 31 P. (d,g) Overlay images of r13C (red), 12 C 14 N (green), and 31 P (blue). (e,f,h-k) Corresponding TEM of (a-d,g). G, glycogen; M, mitochondrion; L, lipid body; P, polyphosphate. Arrows, Candidatus Moeniiplasma glomeromycotorum; arrowheads, Candidatus Glomeribacter gigasporarum. Dashed squares in (e,f,h) show areas corresponding to (i,j,k), respectively. Bars: (a-e), 5 μm; (f-h), 2 μm; (i-k), 0.5 μm.
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Arbuscular mycorrhizal fungi are obligate symbionts of land plants; furthermore, some of the species harbor endobacteria. Although the molecular approach increased our knowledge of the diversity and origin of the endosymbiosis and its metabolic possibilities, experiments to address the functions of the fungal host have been limited. In this study,...
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Several Pleurotus species (oyster mushrooms) are commercially cultivated in India owing to the favorable tropical agro-climatic conditions. However, there are only a few studies on the microbiome of mushrooms, especially oyster mushrooms. The aim of this study was to assess the effect of endobacteria on mycelial growth, spawning, sporophore develop...
Several Pleurotus species (oyster mushrooms) are commercially cultivated in India owing to the favorable tropical agro-climatic conditions. However, there are only a few studies on the microbiome of mushrooms, especially oyster mushrooms. The aim of this study was to assess the effect of endophytic bacteria on mycelial growth, spawning, sporophore...
Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria.
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Harnessing the plant microbiome has the potential to improve agricultural yields and protect plants against pathogens and/or abiotic stresses, while also relieving economic and environmental costs of crop production. While previous studies have gained valuable insights into the underlying genetics facilitating plant-fungal interactions, these have...
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... MRE are detected in diverse lineages of Mucoromycota, but their evolutionary history and impact on host physiology remain largely undetermined 12,15,19 . However, it was determined in Gigaspora margarita that more carbon is directed from fungal hosts to MRE than BRE, possibly indicating an increased cost of hosting MRE compared to BRE 20 . ...
Diverse members of early-diverging Mucoromycota, including mycorrhizal taxa and soil-associated Mortierellaceae, are known to harbor Mollicutes-related endobacteria (MRE). It has been hypothesized that MRE were acquired by a common ancestor and transmitted vertically. Alternatively, MRE endosymbionts could have invaded after the divergence of Mucoromycota lineages and subsequently spread to new hosts horizontally. To better understand the evolutionary history of MRE symbionts, we generated and analyzed four complete MRE genomes from two Mortierellaceae genera: Linnemannia (MRE-L) and Benniella (MRE-B). These genomes include the smallest known of fungal endosymbionts and showed signals of a tight relationship with hosts including a reduced functional capacity and genes transferred from fungal hosts to MRE. Phylogenetic reconstruction including nine MRE from mycorrhizal fungi revealed that MRE-B genomes are more closely related to MRE from Glomeromycotina than MRE-L from the same host family. We posit that reductions in genome size, GC content, pseudogene content, and repeat content in MRE-L may reflect a longer-term relationship with their fungal hosts. These data indicate Linnemannia and Benniella MRE were likely acquired independently after their fungal hosts diverged from a common ancestor. This work expands upon foundational knowledge on minimal genomes and provides insights into the evolution of bacterial endosymbionts.
... Outside of the model system G. margarita BEG34, understanding of functional effects of endobacteria on their Glomeromycotina hosts is still in its infancy. A recent study revealed C flux within a quadruplet symbiosis that included Allium roots and Gigaspora margarita MAFF520054 that hosts both BRE and MRE (Kuga et al. 2021). Using C13 isotope labeling, C flow was followed from the plant to fungi to BRE and MRE and showed that MRE represent a higher cost to their fungal host in terms of carbon compared to BRE (Kuga et al. 2021). ...
... A recent study revealed C flux within a quadruplet symbiosis that included Allium roots and Gigaspora margarita MAFF520054 that hosts both BRE and MRE (Kuga et al. 2021). Using C13 isotope labeling, C flow was followed from the plant to fungi to BRE and MRE and showed that MRE represent a higher cost to their fungal host in terms of carbon compared to BRE (Kuga et al. 2021). These observations corroborate the hypothesis that MRE is more opportunistic than BRE. ...
... Desirò and colleagues showed that MRE bacteria are present in Lobosporangium transversale, Linnemannia elongata, L. gamsii, Mortierella capitata, M. thaxteri, Podila humilis, P. minutissima, Lunasporangiospora selenospora, and L. rostafinskii (Desirò et al. 2018) (Fig. 8.2, Table 8.2). Given their presence in Glomeromycotina (Naumann et al. 2010), Mucoromycotina (Desirò et al. 2018), MRE are hypothesized to be widely distributed amongst Mucoromycota fungi and commensal or opportunistic symbionts (Kuga et al. 2021). ...
Endosymbiotic bacteria are commonly inhabitants of environmental isolates of Mucoromycota fungi. Described bacterial endosymbionts of Mucoromycota are related to Burkholderia and Mycoplasma lineages. Bacterial endosymbionts of Mucoromycota tend to be obligately dependent on their fungal host for nutrition, but bacterial endosymbionts are not always needed for normal vegetative growth by their fungal hosts. When present in the fungal cytosol, bacterial endosymbionts alter fungal physiology including gene expression, protein synthesis, metabolism, and sporulation. Many bacterial endosymbionts have steamlined genomes due to reductive evolution, and the categories of functional gene loss differ by fungal host lineage. Much remains to be learned about bacterial endosymbionts of fungi regarding their ubiquity, transmission, and fungal host interactions.KeywordsMycoavidus, Mycetohabitans, Candidatus Glomeribacter, Phylogenomics, Co-evolution, Fungal–bacterial interactions
... B Also shows the rhizosphere, rhizoplane, endosphere, mycorrhizosphere, and hyphosphere biotopes ◂ obligate endobacteria are biotrophic and rely on their hosts for carbon, nitrogen (amino acids, nucleic acids, and vitamins), and phosphorus, they are difficult to study in vitro (Jargeat et al. 2004;Lumini et al. 2007;Alabid et al. 2019). Although, multiple OMICS studies involving metagenomics, metatranscriptomics, and metabolomics have revealed important details about the influence of obligate endobacterial symbionts on hosts' pre-and post-symbiotic lifestyles (Dearth et al. 2018;Venice et al. 2020a, b;Kuga et al. 2021;Venice et al. 2021), the possible roles in plant growth remain unclear. ...
... AAB dwelling on spore walls can derive nutrients from the outer hyaline layer, which is rich in nutrient sources such as chitin, protein, and fatty acids (Roesti et al. 2005;Cruz et al. 2008;González-Chávez et al. 2008;Selvakumar et al. 2016). The mode of feeding among the cultivable endobacteria, however, has yet to be studied, although studies have confirmed endocellular biotrophy among obligate endobacteria (Ghignone et al. 2012; Kuga et al. 2021). The colonization of fungal cytoplasm by cultivable bacteria other than heritable obligate endobacteria raises questions about mechanisms that govern invasion as well as the integrity of the fungal immune system. ...
Arbuscular mycorrhizal fungi (AMF) are essential components of the plant root mycobiome and are found in approximately 80% of land plants. As obligate plant symbionts, AMF harbor their own microbiota, both inside and outside the plant root system. AMF-associated bacteria (AAB) possess various functional traits, including nitrogen fixation, organic and inorganic phosphate mobilization, growth hormone production, biofilm production, enzymatic capabilities, and biocontrol against pathogen attacks, which not only contribute to the health of the arbuscular mycorrhizal symbiosis but also promote plant growth. Because of this, there is increasing interest in the diversity, functioning, and mechanisms that underlie the complex interactions between AMF, AAB, and plant hosts. This review critically examines AMF-associated bacteria, focusing on AAB diversity, the factors driving richness and community composition of these bacteria across various ecosystems, along with the physical, chemical, and biological connections that enable AMF to select and recruit beneficial bacterial symbionts on and within their structures and hyphospheres. Additionally, potential applications of these bacteria in agriculture are discussed, emphasizing the potential importance of AMF fungal highways in engineering plant rhizosphere and endophyte bacteria communities, and the importance of a functional core of AAB taxa as a promising tool to improve plant and soil productivity. Thus, AMF and their highly diverse bacterial taxa represent important tools that could be efficiently explored in sustainable agriculture, carbon sequestration, and reduction of greenhouse gas emissions related to nitrogen fertilizer applications. Nevertheless, future studies adopting integrated multidisciplinary approaches are crucial to better understand AAB functional diversity and the mechanisms that govern these tripartite relationships.
In addition to abundant animal communities, corals from all ocean depths support diverse microbial associates that are important to coral health. While some of these microbes have been classified taxonomically, understanding the metabolic potential of coral-associated bacteria and how they interact with their coral hosts is limited by a lack of genomic data. One example is Mycoplasma and other members of the class Mollicutes which are widespread coral associates. Here we investigated the association between two novel members of the class Mollicutes and the deep-sea octocoral Callogorgia delta . We screened C. delta , a closely related species C. americana , sediment, and water for mollicutes using 16S metabarcoding. One ASV was found in most colonies screened (99/108) and often dominated the microbiome (up to 99%). Another ASV was detected at lower abundance and prevalence in these corals. Both were absent in all water and were absent or rare in the sediment. We sequenced metagenomes and metatranscriptomes to assemble and annotate genomes and propose the names Ca. Oceanoplasma callogorgiae and Ca. Thalassoplasma callogorgiae . The genomes were small, revealed a reliance on the arginine dihydrolase pathway for ATP production, and contained CRISPR-Cas systems with extensive arrays. CARD-FISH microscopy unveiled an abundant bacterium in the mesoglea which is likely to be Ca. O. callogorgiae . These novel mollicutes cluster with others from diverse invertebrate hosts. Altogether, this work describes the association of these novel mollicutes in C. delta , provides insight into widespread coral associates, and identifies a novel clade of marine mollicutes whose diversity remains largely undiscovered.
