Detection of Betaproteobacteria inside the Mycelium of the Fungus Mortierella elongata

Abstract

Microscopic and molecular analyses showed the presence of endobacteria inside the mycelia of four out of twelve nitrous oxide (N 2 O)-producing fungal isolates identified as Mortierella elongata. The 16S rRNA gene was successfully amplified with DNA extracted directly from the endobacterium-containing fungal strains and all sequences were related to that of Candidatus Glomeribacter gigasporarum in the family Burkholderiaceae. Bacterial endotoxin was detected in the endobacterium-positive fungal strains but only trace levels were found in endobacterium-negative strains. No significant relationship was found between the fungal N 2 O-producing activity and the presence of endobacteria.Key words: endobacterium, N 2 O production, Mortierella elongata, soil fungusThe intracellular distribution of bacteria, or more specifically bacterial endosymbiosis, is known for numerous eukaryotic organisms including ciliate protozoa (25), various insects (11), a frenulata (marine invertebrate) (12), and wellknown legume roots. Concerning the association of bacteria with fungi, bacterial endosymbiosis has been reported in some strains of Glomeromycota [e.g. Geosiphon pyriform (22), and Gigaspora and Scutellospora species (4, 6, 7, 15)], Ascomycota [e.g. Tuber borchii (1)], Basidiomycota [e.g. Laccaria bicolor; (3)] and Zygomycota [e.g. Rhizopus species (10, 18)]. In our recent study, nitrous oxide (N 2 O)-producing fungal strains were isolated from upland soils and the intramycelial localization of bacterium (endobacterium) in the fungal isolates was found (Sato, Y., et al. 2008. Abstracts for the 12th International Symposium on Microbial Ecology, Cairns, Australia). The purpose of this study is to examine further the presence of endobacteria using fluorescence and electron microscopy, the amount of endotoxin, the 16S rRNA gene, and the relationship between the presence of endobacteria and fungal N 2 O-producing activity.Ten fungal strains used in this study were isolated from no-tilled, low-nitrogen input cropland soils at the Field Science Center, Ibaraki University College of Agriculture, located in the Kanto plains of Japan and were identified as phylum Zygomycota, Mortierella elongata from their morphological characteristics and their 18S-26S/28S internal transcribed spacer sequence (ITS). All of the M. elongata strains were examined for activity to produce N 2 O and found to have low activity levels during growth in cultures containing 10 mM nitrite but no activity in cultures with 10 mM nitrate (Y. Sato, T. Nishizawa, M. Umezu, K. Tsuruta, K. Narisawa, M. Komatsuzaki, N. Kaneko, H. Ohta, submitted for publication). Comparisons were made with herbarium materials, Mortierella elongata Linnemann NBRC 8570 and M. elongata MAFF 425591, obtained from the National Institute of Technology and Evaluation (NITE Biological Resource Center, Chiba, Japan), and National Institute of Agrobiological Sciences (NIAS Genebank, Ibaraki, Japan), respectively.The morphology of M. elongata strains was observed by fluorescence microscope. Briefly, ...

Detection of a novel intracellular microbiome hosted in arbuscular mycorrhizal fungi

“…There is, however, increasing evidence that Mortierella species (Mucoromycotina) host endobacteria that are related to CaGg (Sato et al, 2010;Kai et al, 2012;Bonito et al, 2013). These data open a novel interesting scenario: fungal endobacteria might prefer coenocytic hyphae.…”

Isolation of Endohyphal Bacteria from Foliar Ascomycota and In Vitro Establishment of Their Symbiotic Associations

“…One example of these microbial symbioses is that between plant-associated fungi and their bacterial endosymbionts (endobacteria, endofungal bacteria, or endohyphal bacteria [EHB]). Recent studies have indicated that EHB are widespread in rhizosphere fungi from diverse fungal phyla (e.g., mycorrhizal and pathogenic fungi from the Basidiomycota, Glomeromycota, and Mucoromycotina [6][7][8][9][10][11][12][13]) and in the highly diverse Ascomycota that infect roots, stems, and leaves as endophytes (14) (class 3 endophytes, sensu [15]). However, functional relationships have been studied for only a few associations, limiting inferences regarding the scope and potential importance of EHB-fungal associations in ecological interactions and human applications (but see references 16 and 17).…”

“…Most studies aimed at understanding functional relationships between EHB and fungi have focused on root-associated fungi, especially arbuscular mycorrhizal fungi in the Glomeromycota and plant-pathogenic Rhizopus in the Mucoromycotina (6)(7)(8)(9)(10)(11)(18)(19)(20)(21)(22)(23). EHB in rhizosphere fungi are often vertically transmitted and host specific, and they frequently maintain obligate relationships with their hosts (18)(19)(20).…”

The ecological role of volatile mediated interactions belowground

“…increasing the fungal sporulation success and raising the fungal bioenergetics capacity (Salvioli et al 2016). Another well-studied example is the rice seedling Microscopic and molecular analysis showed that several nitrous oxide-producing fungal isolates of Mortierella elongata harboured endobacteria in their mycelia (Sato et al 2010). The sequencing of 16S rRNA genes revealed that the N 2 O-producing fungus…”

“…Mortierella elongate harbored endobacteria belonging to the family Burkholderiacea, however, the significance of this fungal-bacterial association is unknown (Sato et al 2010).…”