Comparative Genomic Insights into Endofungal Lifestyles of Two Bacterial Endosymbionts, <i>Mycoavidus cysteinexigens</i> and <i>Burkholderia rhizoxinica</i>

Abstract

Endohyphal bacteria (EHB), dwelling within fungal hyphae, markedly affect the growth and metabolic potential of their hosts. To date, two EHB belonging to the family Burkholderiaceae have been isolated and characterized as new taxa, Burkholderia rhizoxinica (HKI 454T) and Mycoavidus cysteinexigens (B1-EBT), in Japan. Metagenome sequencing was recently reported for Mortierella elongata AG77 together with its endosymbiont M. cysteinexigens (Mc-AG77) from a soil/litter sample in the USA. In the present study, we elucidated the complete genome sequence of B1-EBT and compared it with those of Mc-AG77 and HKI 454T. The genomes of B1-EBT and Mc-AG77 contained a higher level of prophage sequences and were markedly smaller than that of HKI 454T. Although the B1-EBT and Mc-AG77 genomes lacked the chitinolytic enzyme genes responsible for invasion into fungal cells, they contained several predicted toxin-antitoxin systems including an insecticidal toxin complex and PIN domain imposing an addiction-like mechanism essential for endohyphal growth control during host colonization. Despite the different host fungi, the alignment of amino acid sequences showed that the HKI 454T genome consisted of 1,265 (32.6%) and 1,221 (31.5%) orthologous coding sequences (CDSs) with those of B1-EBT and Mc-AG77, respectively. This comparative study of three phylogenetically associated endosymbionts has provided insights into their origin and evolution, and suggests the later bacterial invasion and adaptation of B1-EBT to its host metabolism.

Growing edible mushrooms: a conversation between bacteria and fungi

“…The microbiome of Inocybe terrigena (scaly fibre head) fruiting-bodies also includes bacteria showing symbiotic functions, regardless of habitat conditions (Bahram et al, 2018). Among the symbiotic bacteria reported by the cited authors to inhabit the I. terrigena basidiomes: the genus Pseudomonas is, as already reported above, associated with mushroom fructification (Colauto et al, 2016), Pedobacter species are noted for carrying a large number and variety of antimicrobial resistance genes (Viana et al 2018), and have been reported to detoxify tolaasin produced by the mushroom pathogen Pseudomonas tolaasii (Tsukamoto et al, 2002) and Burkholderia members have been reported to enter into beneficial interactions with mycorrhizal and other fungi, including intracellular symbioses (Frey-Klett et al, 2011;Sharmin et al 2018). Table 1 compiles recent literature describing bacteria associated with the mycelium and fruit bodies, including the techniques employed to characterize the microbiome, methods implemented and role reported.…”

“…), and have been reported to detoxify tolaasin produced by the mushroom pathogen Pseudomonas tolaasii (Tsukamoto et al ., ) and Burkholderia members have been reported to enter into beneficial interactions with mycorrhizal and other fungi, including intracellular symbioses (Frey‐Klett et al ., ; Sharmin et al . ). Table compiles recent literature describing bacteria associated with the mycelium and fruit bodies, including the techniques employed to characterize the microbiome, methods implemented and role reported.…”

Environmental interactions with amoebae as drivers of bacterial-fungal endosymbiosis and pathogenicity

“…Fungi harbor a wide diversity of bacterial endosymbionts that are specifically adapted to colonize their fungal hosts and significantly influence host-relevant fungal phenotypes, including metabolism, cell wall organization, development, and plant host colonization 35,58,59,81,90,94,96-106 . Additionally, endobacteria are a source of potent mycotoxins that can influence fungal pathogenesis in plants and insects 59,60,81,90,107,108 . New patient populations are now susceptible to a broadening diversity of basal saprobic fungi, which are a major emerging cause of clinically important superficial and disseminated fungal infections 18,109 .…”

Aposymbiosis of a <i>Burkholderiaceae</i>-Related Endobacterium Impacts on Sexual Reproduction of Its Fungal Host

“…BRE were generally found in hyphae and asexual spores (Lumini et al, 2007;Sato et al, 2010;Ohshima et al, 2016;Mondo et al, 2017;Takashima et al, 2018a) as well as in sexual spores (Mondo et al, 2017). The host nutrient dependence of BRE due to genome reductions was suggested by genomic studies (Ghignone et al, 2012;Fujimura et al, 2014;Uehling et al, 2017;Sharmin et al, 2018). However, limited information is currently available on the effects of BRE on their fungal hosts.…”