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The Mucorales is a group of ancient fungi with global distribution. In the current study we accessed mucoralean fungi isolated from two countries on opposite sides of the Earth and in different hemispheres: South Korea and Brazil. Mucorales isolates were obtained from freshwater, soil, invertebrates, and fruit seeds and identified using phenotypic techniques combined with the DNA sequence data. These analyses revealed 15 new species including one that we affiliated to a newly proposed genus, Neofennellomyces. Names proposed for these 15 new species are Absidia cheongyangensis, A. fluvii, A. kunryangriensis, A. paracylindrospora, A. tarda, A. variiprojecta, A. variispora, Backusella varians, Mucor albicolonia, M. aurantiacus, M. cryophilus, M. glutinatus, M. paraorantomantidis, M. timomeni, and Neofennellomyces jeongsukae. Of these new species, 12 were isolated from South Korea: A. cheongyangensis, A. fluvii, A. kunryangriensis, A. paracylindrospora, B. varians, M. albicolonia, M. aurantiacus, M. cryophilus, M. glutinatus, M. paraorantomantidis, M. timomeni, and N. jeongsukae, and three from Brazil: A. tarda, A. variiprojecta, and A. variispora. Niche specificity of these fungi is discussed including newly recorded invertebrate hosts and a new geographic distribution for species of Backusella, Circinella, Cunninghamella, and Mucor. Given these findings, we provide an inventory of Mucorales. [ABSTRACT FROM AUTHOR]

Gongronella had accommodated only two species for more than half a century and as many as 17 new species have been described in this genus since 2015. However, no systematic studies were conducted for this genus so far. The distribution, substrate and morphology of all known species in Gongronella are analysed herein. Meanwhile, with the support of phylogenetic and morphological evidence, six new species (G. abortosporangia sp. nov., G. apophysata sp. nov., G. bawanglingensis sp. nov., G. inconstans sp. nov., G. pingtangensis sp. nov. and G. reniformis sp. nov.) are proposed and G. pamphilae is recorded from China for the first time. The phylogenetic tree was constructed using ITS+LSU+TEF+ACT+RPB1 and the results were basically the same as ITS+LSU. All species of Gongronella, except G. namwonensis from fresh water, were isolated from soil. The genus is distributed worldwide, mainly in tropical and subtropical regions. A synoptic key is provided for a total of 24 species (18 species previously published and six species newly described herein), except for G. banzhaoae due to unavailable protologue, type and living culture. No morphologies were described when G. pamphilae was proposed. Thanks to the strains isolated in this study, G. pamphilae is included in the key and reported as a Chinese new record. This is the first comprehensive taxonomy and phylogeny of the genus Gongronella. [ABSTRACT FROM AUTHOR]

Many social insect species build nests, which differ from the surrounding environment and are often occupied by specific organismal communities. These organisms may interact mutualistically or parasitically with the nest‐builders, or simply co‐occur, being able to survive in these microenvironments. In temperate forests, red wood ants (e.g. Formica polyctena) are known to create distinct, highly developed nests, which consist of large, above‐ground mounds, built primarily out of plant matter collected from the forest litter. The microorganismal communities of such mounds remain understudied. As representatives of Mucoromycota fungi commonly engage in the decomposition process of the forest litter, they would be expected to occur in the mounds. However, it is still not known whether the Mucoromycota community of these ants' nests differ from the one of the surrounding forest litter. In order to distinguish mound‐associated taxa, we characterized Mucoromycota communities of Formica polyctena mounds and the surrounding forest litter. We sampled four sites, twice in a season. Sampled material was plated on agar media and emerging Mucoromycota colonies were identified based on their morphology. Fungal identification was further confirmed using DNA barcoding. In order to compare described communities, PERMANOVA test and non‐metric multidimensional scaling ordinations were used. To distinguish taxa associated with the mounds, multilevel pattern analysis was performed. Our results show that the Mucoromycota community of Formica polyctena's mound differs from the community of the surrounding forest litter. While representatives of Entomortierella lignicola and Absidia cylindrospora clade were found to be associated with the mound environment, representatives of Umbelopsis curvata and Podila verticillata‐humilis clade were associated with forest litter, and were rarely present in the mounds. Our findings strongly suggest that the red wood ants' nest is a specific microenvironment in the temperate forest floor, which is a preferred microhabitat for the mound‐associated Mucoromycota, possibly adapted to live in proximity to ants. [ABSTRACT FROM AUTHOR]

Bats (Chiroptera), the second largest group of mammals, are known for their unique immune system and their ability to act as vectors for various zoonoses. Bats also act as important carriers of fungi, which include plant, animal, and human pathogens. Their roosting areas, foraging behaviors, and even migration routes make bats ideal vectors for fungi. We isolated 75 culturable fungal species from bats in Yunnan Province, China, with 36 species representing known pathogens of plants, animals, and humans, while 39 species are non-pathogenic fungi. Among these species, 77% (58 species) belonged to Ascomycota, 9% (seven species) belonged to Basidiomycota, and 13% (10 species) belonged to Mucoromycota. Even though several taxonomic studies on fungi associated with bats have been published, studies exploring the role of bats as fungal vectors are lacking. This study discusses the fungi host-specific traits and pathogenicity and the impact and ecological significance of bats as fungal vectors. [ABSTRACT FROM AUTHOR]

Most Mucoromycota fungi form zygospores as sexual reproductive structures. When two colonies of compatible strains meet, zygospores are formed in the area where the colonies meet. The structure and development of zygospores have been studied for a long time by light microscopy and electron microscopy. This study is the first time-lapse report on the dynamic movements of sexual and asexual reproductive processes by live imaging in Gilbertella persicaria (Choanephoraceae, Mucorales). Our live imaging analysis indicated the formation of zygospores begin immediately after two aerial hyphae contact whether at the tip or middle of the hyphae. The early-stage zygospores elongated from the contact site with a rate of 1.2-1.7 µm/s and reach < 200 µm in 2-3 h. Following maturation of zygospores, from progametangia to gametangia and maturation stage, took a few hours, in total 5 to 6 h after the first contact of two hyphae. When a zygospore was formed near the tip of hypha in contact with the partner hypha, the hyphal growth ceased. When zygospore was formed behind the tip of the hypha, the hyphal growth continued without slowing down. This study provides quantitative spatio-temporal information on the dynamics of zygospore formation. [ABSTRACT FROM AUTHOR]

Abstract Many social insect species build nests, which differ from the surrounding environment and are often occupied by specific organismal communities. These organisms may interact mutualistically or parasitically with the nest‐builders, or simply co‐occur, being able to survive in these microenvironments. In temperate forests, red wood ants (e.g. Formica polyctena) are known to create distinct, highly developed nests, which consist of large, above‐ground mounds, built primarily out of plant matter collected from the forest litter. The microorganismal communities of such mounds remain understudied. As representatives of Mucoromycota fungi commonly engage in the decomposition process of the forest litter, they would be expected to occur in the mounds. However, it is still not known whether the Mucoromycota community of these ants' nests differ from the one of the surrounding forest litter. In order to distinguish mound‐associated taxa, we characterized Mucoromycota communities of Formica polyctena mounds and the surrounding forest litter. We sampled four sites, twice in a season. Sampled material was plated on agar media and emerging Mucoromycota colonies were identified based on their morphology. Fungal identification was further confirmed using DNA barcoding. In order to compare described communities, PERMANOVA test and non‐metric multidimensional scaling ordinations were used. To distinguish taxa associated with the mounds, multilevel pattern analysis was performed. Our results show that the Mucoromycota community of Formica polyctena's mound differs from the community of the surrounding forest litter. While representatives of Entomortierella lignicola and Absidia cylindrospora clade were found to be associated with the mound environment, representatives of Umbelopsis curvata and Podila verticillata‐humilis clade were associated with forest litter, and were rarely present in the mounds. Our findings strongly suggest that the red wood ants' nest is a specific microenvironment in the temperate forest floor, which is a preferred microhabitat for the mound‐associated Mucoromycota, possibly adapted to live in proximity to ants.

Aims To investigate fatty acid, including polyunsaturated fatty acids (PUFA), and cerebroside production of a large diversity of fungi from the Ascomycota, Basidiomycota , and Mucoromycota phyla. Methods and results Seventy-nine fungal strains were grown in Kavadia medium using a microcultivation system, i.e. Duetz microtiter plates. Following cultivation, fatty acid and cerebroside contents were analyzed by gas chromatography-flame ionization detection (GC-FID) and high performance thin-layer chromatography (HPTLC), respectively. Mucoromycota fungi appeared as the most promising candidates for omega-6 PUFA production. The best omega-6 producer, including γ-linolenic acid (GLA, 18:3n-6), was Mucor fragilis UBOCC-A109196 with a concentration of 647 mg L−1 total omega-6 PUFA (representing 35% of total fatty acids) and 225 mg L−1 GLA (representing 12% of total fatty acids). Arachidonic acid concentration (20:4n-6) was the highest in Mortierella alpina UBOCC-A-112046, reaching 255 mg L−1 and 18.56% of total fatty acids. Interestingly, several fungal strains were shown to produce omega-7 monounsaturated fatty acids. Indeed, Torulaspora delbrueckii strains accumulated palmitoleic acid (16:1n-7) up to 20% of total fatty acids, reaching 114 mg L−1 in T. delbrueckii UBOCC-A-214128, while C. elegans UBOCC-A-102008 produced mainly paullinic acid (20:1n-7) with concentrations up to 100 mg L−1. Concerning cerebroside production, HPTLC appeared as a relevant approach for their detection and quantification. Promising candidates belonging to the Mucoromycota phylum were found, especially in the Absidia genus with A. spinosa UBOCC-A-101332 as the best producer (12.7 mg L−1). Conclusions The present study highlighted PUFA and cerebroside production in a large diversity of fungi and the fact that members of the Mucoromycota phylum are good producers of PUFA as well as cerebrosides. [ABSTRACT FROM AUTHOR]

The genus Gongronella is important in agriculture and industry by secreting various natural bioactive metabolites such as chitosanases and organic acids. During the most recent 8 years, a total of 14 new species have been described, remarkably enriching the diversity of this genus. In this study, we added three more new species to this valuable genus, based on a combination of morphological traits and phylogenetic information. Six strains of the genus Gongronella were isolated from soil collected in Hainan Province, China. Phylogenetic analyses of ITS and LSU rDNA sequences grouped these strains into three independent clades. According to their unique morphological characteristics, they were classified as G. multiramosa sp. nov., G. qichaensis sp. nov. and G. oleae sp. nov. The G. multiramosa was characterized by multiple branched sporangiophores and was closely related to G. pedratalhadensis. The G. qichaensis was characterized by obscure collars and closely related to G. butleri, G. hydei and G. banzhaoae. The G. oleae was characterized by the presence of oil droplets in the sporangiospores and was closely related to G. chlamydospora and G. multispora. Their descriptions and illustrations were provided, and their differences from morphological allies and phylogenetic-related species are discussed. [ABSTRACT FROM AUTHOR]

Mucor species are a group of common soil-borne fungi, known to cause infections on humans and animals, interfere in food production, and act as useful agents in biotechnological applications. This study reports one new Mucor species, M. yunnanensis, which was found to be fungicolous on an Armillaria sp. from southwest China. Further, M. circinelloides on Phlebopus sp., M. hiemalis on Ramaria sp. and Boletus sp., M. irregularis on Pleurotus sp., M. nederlandicus on Russula sp., and M. yunnanensis on Boletus sp. are reported as new host records. Mucor yunnanensis and M. hiemalis have been collected from Yunnan Province in China, whereas M. circinelloides, M. irregularis, and M. nederlandicus have been collected from Chiang Mai and Chiang Rai Provinces in Thailand. All the Mucor taxa reported herein were identified based on both morphology and phylogenetic analyses of a combined nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS) and partial nuc 28S rDNA (28S) sequence matrix. Comprehensive descriptions, illustrations, and a phylogenetic tree are provided for all the taxa reported in the study to show the placements of taxa, and the new taxon is compared with its sister taxa. [ABSTRACT FROM AUTHOR]

Species of Lichtheimia are important opportunistic fungal pathogens in the order Mucorales that are isolated from various sources such as soil, indoor air, food products, feces, and decaying vegetables. In recent years, species of Lichtheimia have become an emerging causative agent of invasive mucormycosis. In Europe and USA, Lichtheimia are the second and third most common causal fungus of mucormycosis, respectively. Thus, the aim of this study was to survey the diversity of species of Lichtheimia hidden in poorly studied hosts, such as invertebrates, in Korea. Eight Lichtheimia strains were isolated from invertebrate samples. Based on morphology, physiology, and phylogenetic analyses of ITS and LSU rDNA sequence data, the strains were identified as L. hyalospora, L. ornata, L. ramosa, and a novel species, L. koreana sp. nov. Lichtheimia koreana is characterized by a variable columellae, sporangiophores arising solitarily or up to three at one place from stolons, and slow growth on MEA and PDA at all temperatures tested. The new species grows best at 30 and 35 °C and has a maximum growth temperature of 40 °C. Detailed descriptions, illustrations, and a phylogenetic tree are provided. [ABSTRACT FROM AUTHOR]

The mucoralean genus Backusella comprises saprobe species commonly isolated from soil and leaf litter but also from wood, invertebrates, and toads. Molecular species recognition of Backusella has been mainly based on the ITS and LSU regions. Because mucoralean fungi tend to have high intraspecific variability of ITS sequences, we established the gene encoding the largest subunit of RNA polymerase II (RPB1) as phylogenetic marker in Backusella. The topologies of the ITS/LSU and RPB1 trees were widely similar. The maximum growth temperature is shown to represent a valuable taxonomic feature because it varied strongly within the genus. Seven Backusella spp. are capable of growing at temperatures ≥ 36 °C, four of which were positioned in a same clade. Based on the evidence of molecular phylogenetic analyses as well as on morphological and physiological (maximum growth temperature) features, Backusella gigaspora sp. nov. and B. pernambucensis sp. nov. are described. [ABSTRACT FROM AUTHOR]

The genus Gongronella is important in agriculture and industry by secreting various natural bioactive metabolites such as chitosanases and organic acids. During the most recent 8 years, a total of 14 new species have been described, remarkably enriching the diversity of this genus. In this study, we added three more new species to this valuable genus, based on a combination of morphological traits and phylogenetic information. Six strains of the genus Gongronella were isolated from soil collected in Hainan Province, China. Phylogenetic analyses of ITS and LSU rDNA sequences grouped these strains into three independent clades. According to their unique morphological characteristics, they were classified as G. multiramosa sp. nov., G. qichaensis sp. nov. and G. oleae sp. nov. The G. multiramosa was characterized by multiple branched sporangiophores and was closely related to G. pedratalhadensis. The G. qichaensis was characterized by obscure collars and closely related to G. butleri, G. hydei and G. banzhaoae. The G. oleae was characterized by the presence of oil droplets in the sporangiospores and was closely related to G. chlamydospora and G. multispora. Their descriptions and illustrations were provided, and their differences from morphological allies and phylogenetic-related species are discussed.

The presence of viruses is less explored in Mucoromycota as compared to other fungal groups such as Ascomycota and Basidiomycota. Recently, more and more mycoviruses are identified from the early-diverging lineages of fungi. We have determined the genome of 11 novel dsRNA viruses in seven different Umbelopsis strains with next-generation sequencing (NGS). The identified viruses were named Umbelopsis ramanniana virus 5 (UrV5), 6a (UrV6a); 6b (UrV6b); 7 (UrV7); 8a (UrV8a); 8b (UrV8b); Umbelopsis gibberispora virus 1 (UgV1); 2 (UgV2) and Umbelopsis dimorpha virus 1a (UdV1a), 1b (UdV1b) and 2 (UdV2). All the newly identified viruses contain two open reading frames (ORFs), which putatively encode the coat protein (CP) and the RNA-dependent RNA polymerase (RdRp), respectively. Based on the phylogeny inferred from the RdRp sequences, eight viruses (UrV7, UrV8a, UrV8b, UgV1, UgV2, UdV1a, UdV1b and UdV2) belong to the genus Totivirus, while UrV5, UrV6a and UrV6b are placed into a yet unclassified but well-defined Totiviridae-related group. In UrV5, UgV1, UgV2, UrV8b, UdV1a, UdV2 and UdV1b, ORF2 is predicted to be translated as a fusion protein via a rare +1 (or −2) ribosomal frameshift, which is not characteristic to most members of the Totivirus genus. Virus particles 31 to 32 nm in diameter could be detected in the examined fungal strains by transmission electron microscopy. Through the identification and characterization of new viruses of Mucoromycota fungi, we can gain insight into the diversity of mycoviruses, as well as into their phylogeny and genome organization. [ABSTRACT FROM AUTHOR]

Umbelopsis ramanniana is one of the most commonly reported species within the genus and an important oleaginous fungus. The morphology of the species varies remarkably in sporangiospores, columellae and chlamydospores. However, phylogenetic analyses based on ITS and nLSU rDNA had previously shown insufficiency in achieving species level identification in the genus Umbelopsis. In this study, by applying a polyphasic approach involving multi-gene (nSSU, ITS, nLSU, act1, MCM7 and cox1) phylogeny, morphology and maximum growth temperature, U. ramanniana sensu lato was revealed as a polyphyletic group and resolved with five novel taxa, namely U. curvata, U. dura, U. macrospora, U. microsporangia and U. oblongielliptica. Additionally, a key for all currently accepted species in Umbelopsis was also updated. [ABSTRACT FROM AUTHOR]

Although species of Absidia are known to be ubiquitous in soil, animal dung, and insect and plant debris, the species diversity of the genus and their ecological habitats have not been sufficiently investigated. In this study, we describe five new species of Absidia from forest and grassland soils in southwestern China, with support provided by phylogenetic, morphological, and physiological evidence. The species diversity and ecological habitat of Absidia are summarized. Currently, 22 species are recorded in China, which mainly occur in soil, especially in tropical and subtropical forests and mountains. An updated key to the species of Absidia in China is also provided herein. This is the first overview of the Absidia ecological habitat. [ABSTRACT FROM AUTHOR]

Gongronella is a genus of fungi in Mucorales (Mucoromycota). Some of its members have important biotechnological applications, but until now, not a single mitogenome has been characterized in Gongronella. Here, we present the complete mitogenome assembly of Gongronella sp. w5, a soil isolate known to interact with plants and several fungi. Its 36,593-bp circular mitogenome encodes the large and small subunit rRNAs, 14 standard mitochondrial proteins, 24 tRNAs, three free-standing ORF proteins, and the RNA subunit of RNase P (rnpB). These genes arrange in an order novel to known fungal mitogenomes. Three group I introns are present in the cob, cox1, and nad5 genes, respectively, and they are probably acquired by horizontal gene transfer. Phylogenetic analysis based on mitochondrion-encoded proteins supports the grouping of Gongronella sp. w5 with Absidia glauca, forming the Cunninghamellaceae clade within Mucoromycota. Gongronella and most other Mucoromycota species are predicted to use the standard genetic code in mitochondrial translation, rather than code 4 assigned by GenBank. A comparison among seven publicly available mitogenomes in Mucoromycota reveals the presence of the same 14 typical protein-coding genes plus rnpB, yet substantial variation in mitogenome size, intron number, gene order, and orientation. In this comparison, the uniqueness of Gongronella is evident from similarly large differences to its closest phylogenetic neighbor, A. glauca. This study promotes our understanding of fungal evolution in Mucoromycota. Key points: • This study reports the first mitogenome in Gongronella, which presents a novel gene order. • Different Mucoromycota mitogenomes show substantial variation of gene organizations. • Most Mucoromycota species use the standard genetic code to translate mitochondrial genes. [ABSTRACT FROM AUTHOR]

Species of Lichtheimia are important opportunistic fungal pathogens in the order Mucorales that are isolated from various sources such as soil, indoor air, food products, feces, and decaying vegetables. In recent years, species of Lichtheimia have become an emerging causative agent of invasive mucormycosis. In Europe and USA, Lichtheimia are the second and third most common causal fungus of mucormycosis, respectively. Thus, the aim of this study was to survey the diversity of species of Lichtheimia hidden in poorly studied hosts, such as invertebrates, in Korea. Eight Lichtheimia strains were isolated from invertebrate samples. Based on morphology, physiology, and phylogenetic analyses of ITS and LSU rDNA sequence data, the strains were identified as L. hyalospora, L. ornata, L. ramosa, and a novel species, L. koreana sp. nov. Lichtheimia koreana is characterized by a variable columellae, sporangiophores arising solitarily or up to three at one place from stolons, and slow growth on MEA and PDA at all temperatures tested. The new species grows best at 30 and 35 °C and has a maximum growth temperature of 40 °C. Detailed descriptions, illustrations, and a phylogenetic tree are provided.

The presence of viruses is less explored in Mucoromycota as compared to other fungal groups such as Ascomycota and Basidiomycota. Recently, more and more mycoviruses are identified from the early-diverging lineages of fungi. We have determined the genome of 11 novel dsRNA viruses in seven different Umbelopsis strains with next-generation sequencing (NGS). The identified viruses were named Umbelopsis ramanniana virus 5 (UrV5), 6a (UrV6a); 6b (UrV6b); 7 (UrV7); 8a (UrV8a); 8b (UrV8b); Umbelopsis gibberispora virus 1 (UgV1); 2 (UgV2) and Umbelopsis dimorpha virus 1a (UdV1a), 1b (UdV1b) and 2 (UdV2). All the newly identified viruses contain two open reading frames (ORFs), which putatively encode the coat protein (CP) and the RNA-dependent RNA polymerase (RdRp), respectively. Based on the phylogeny inferred from the RdRp sequences, eight viruses (UrV7, UrV8a, UrV8b, UgV1, UgV2, UdV1a, UdV1b and UdV2) belong to the genus Totivirus, while UrV5, UrV6a and UrV6b are placed into a yet unclassified but well-defined Totiviridae-related group. In UrV5, UgV1, UgV2, UrV8b, UdV1a, UdV2 and UdV1b, ORF2 is predicted to be translated as a fusion protein via a rare +1 (or −2) ribosomal frameshift, which is not characteristic to most members of the Totivirus genus. Virus particles 31 to 32 nm in diameter could be detected in the examined fungal strains by transmission electron microscopy. Through the identification and characterization of new viruses of Mucoromycota fungi, we can gain insight into the diversity of mycoviruses, as well as into their phylogeny and genome organization.

Umbelopsis ramanniana is one of the most commonly reported species within the genus and an important oleaginous fungus. The morphology of the species varies remarkably in sporangiospores, columellae and chlamydospores. However, phylogenetic analyses based on ITS and nLSU rDNA had previously shown insufficiency in achieving species level identification in the genus Umbelopsis. In this study, by applying a polyphasic approach involving multi-gene (nSSU, ITS, nLSU, act1, MCM7 and cox1) phylogeny, morphology and maximum growth temperature, U. ramanniana sensu lato was revealed as a polyphyletic group and resolved with five novel taxa, namely U. curvata, U. dura, U. macrospora, U. microsporangia and U. oblongielliptica. Additionally, a key for all currently accepted species in Umbelopsis was also updated.

Although species of Absidia are known to be ubiquitous in soil, animal dung, and insect and plant debris, the species diversity of the genus and their ecological habitats have not been sufficiently investigated. In this study, we describe five new species of Absidia from forest and grassland soils in southwestern China, with support provided by phylogenetic, morphological, and physiological evidence. The species diversity and ecological habitat of Absidia are summarized. Currently, 22 species are recorded in China, which mainly occur in soil, especially in tropical and subtropical forests and mountains. An updated key to the species of Absidia in China is also provided herein. This is the first overview of the Absidia ecological habitat.

Most Mucoromycota fungi form zygospores as sexual reproductive structures. When two colonies of compatible strains meet, zygospores are formed in the area where the colonies meet. The structure and development of zygospores have been studied for a long time by light microscopy and electron microscopy. This study is the first time-lapse report on the dynamic movements of sexual and asexual reproductive processes by live imaging in Gilbertella persicaria ( Choanephoraceae , Mucorales ). Our live imaging analysis indicated the formation of zygospores begin immediately after two aerial hyphae contact whether at the tip or middle of the hyphae. The early-stage zygospores elongated from the contact site with a rate of 1.2-1.7 µm/s and reach < 200 µm in 2-3 h. Following maturation of zygospores, from progametangia to gametangia and maturation stage, took a few hours, in total 5 to 6 h after the first contact of two hyphae. When a zygospore was formed near the tip of hypha in contact with the partner hypha, the hyphal growth ceased. When zygospore was formed behind the tip of the hypha, the hyphal growth continued without slowing down. This study provides quantitative spatio-temporal information on the dynamics of zygospore formation., (2024, by The Mycological Society of Japan.)

As an endosymbiont of the ecologically and medically relevant fungus Rhizopus microsporus , the toxin-producing bacterium Mycetohabitans rhizoxinica faces myriad challenges, such as evading the host's defense mechanisms. However, the bacterial effector(s) that facilitate the remarkable ability of M. rhizoxinica to freely migrate within fungal hyphae have thus far remained unknown. Here, we show that a transcription activator-like (TAL) effector released by endobacteria is an essential symbiosis factor. By combining microfluidics with fluorescence microscopy, we observed enrichment of TAL-deficient M. rhizoxinica in side hyphae. High-resolution live imaging showed the formation of septa at the base of infected hyphae, leading to the entrapment of endobacteria. Using a LIVE/DEAD stain, we demonstrate that the intracellular survival of trapped TAL-deficient bacteria is significantly reduced compared with wild-type M. rhizoxinica , indicative of a protective host response in the absence of TAL proteins. Subversion of host defense in TAL-competent endobacteria represents an unprecedented function of TAL effectors. Our data illustrate an unusual survival strategy of endosymbionts in the host and provide deeper insights into the dynamic interactions between bacteria and eukaryotes. • TAL effectors circumvent host defense in a bacterial-fungal endosymbiosis • Microfluidics reveal trapping of effector-deficient bacteria in fungal side hyphae • Unprecedented case of septa formation in Mucoromycota fungi • Endosymbionts rely on TAL effectors to aid their intracellular lifestyle Richter et al. show that a transcription activator-like (TAL) effector of bacteria living within a phytopathogenic fungus is an essential symbiosis factor. Microfluidics and live imaging reveal septa formation in fungal side hyphae, which traps TAL effector-deficient bacteria, leading to reduced survival. [ABSTRACT FROM AUTHOR]

Metagenomics approaches have revealed the importance of Mucoromycota in the evolution and functioning of plant microbiomes. Comprised of three subphyla (Glomeromycotina, Mortierellomycotina, and Mucoromycotina), this early diverging lineage of fungi encompasses species of mycorrhizal fungi, root endophytes, plant pathogens, and many decomposers of plant debris. Interestingly, several taxa of Mucoromycota share a common feature, that is, the presence of endobacteria within their mycelia and spores. The study of these endosymbiotic bacteria is still a challenging task. However, given recent improvements in the sensitivity of culture-free approaches, a deeper understanding of such microbial interactions is now possible and fuels an emerging research field. In this chapter, we report how Mucoromycota, in particular Mortierellomycotina, and their endobacteria can be investigated using a combination of diverse cellular biology, microscopy, and molecular techniques., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)