New Endohyphal Relationships between Mucoromycota and Burkholderiaceae Representatives

Abstract

Mucoromycota representatives are known to harbour two types of endohyphal bacteria (EHB) – Burkholderia related endobacteria (BRE) and Mycoplasma related endobacteria (MRE). While both BRE and MRE occur in fungi representing all subphyla of Mucoromycota, their distribution is not well studied. Therefore, it is difficult to resolve the evolutionary history of these associations in favour of one of the two alternative hypotheses explaining their origin: “early invasion” and “late invasion”. Our main goal was to fill this knowledge gap by surveying Mucoromycota fungi for presence of EHB. We screened 196 fungal strains from 16 genera using PCR-based approach to detect bacterial 16S rDNA gene, complemented with FISH imaging to confirm presence of bacteria within the hyphae. We detected Burkholderiaceae in ca. 20% of fungal strains. Some of these bacteria clustered phylogenetically with previously described BRE clades whereas others grouped with free-living Paraburkholderia. Importantly, the latter were detected in Umbelopsidales, which previously were not known to harbour endobacteria. Our results suggest that this group of EHB is recruited from the environment, supporting the late invasion scenario. This pattern complements the early invasion scenario apparent in the BRE clade of EHB. IMPORTANCE Bacteria living within fungal hyphae present an example of one of the most intimate relationships between fungi and bacteria. Even though there are several well-described examples of such partnerships, their prevalence within fungal kingdom remains unknown. Our study focused on early divergent terrestrial fungi in the phylum Mucoromycota. We found that ca. 20% of the strains tested, harboured bacteria from the family Burkholderiaceae. Not only did we confirm the presence of bacteria from previously described endosymbiont clades, we also identified new group of endohyphal Burkholderiaceae representing the genus Paraburkholderia. We established that more than half of the screened Umbelopsis strains were positive for bacteria from this new group. We also determined that, while previously described BRE codiverged with their fungal hosts, Paraburkholderia symbionts did not.

Habitat, Snow-Cover and Soil pH, Affect the Distribution and Diversity of Mortierellaceae Species and Their Associations to Bacteria

“…If endohyphal associations have an ancient origin, the ability to form associations with bacteria could be a common synapomorphic trait in the Mortierellaceae lineage. We detected at least four bacterial species, which, based on their taxonomic placement, are possibly endohyphal (Ohshima et al, 2016;Uehling et al, 2019;Okrasiñska et al, 2021). Mycoavidus cysteinexigens was the most frequently detected one.…”

Whole-Genome Sequence of Entomortierella parvispora E1425, a Mucoromycotan Fungus Associated with Burkholderiaceae -Related Endosymbiotic Bacteria

“…Soilborne fungi of Mortierella spp. harbor Burkholderiaceae -related endobacteria (BRE) ( 1 – 7 ) that can protect the host from nematode attack and inhibit zygospore formation ( 8 , 9 ). Entomortierella parvispora E1425 (JCM 39028, synonymously known as Mortierella parvispora E1425) isolated from forest soil possesses a cultivable BRE named Mycoavidus sp.…”

Linnemannia elongata (Mortierellaceae) stimulates Arabidopsis thaliana aerial growth and responses to auxin, ethylene, and reactive oxygen species

“…Recent studies have demonstrated Mortierellaceae can harbor endobacterial symbionts [ 19 – 22 ]. However, the impacts of endohyphal bacteria on the PGP phenotype have not been assessed.…”