Characterization of Umbelopsis and Paraburkholderia symbiosis

Mucoromycota fungi are known to form close relationships with endohyphal bacteria. However, examples of more facultative interactions with bacteria have been recently reported in this lineage too. One example of facultative, yet endohyphal interaction is Umbelopsis-Paraburkholderia consortium which seems to be highly prevalent in deadwood. As, so far, in-depth characterizations are available only for some strictly endohyphal bacteria and their hosts, we focused on functional genomic characterization of one facultative partnership, as well as confirming its endohyphal nature. In order to characterize this partnership, we compared both partners with their free-living and symbiotic relatives. The genomes of both partners were sequenced on Nanopore and Illumina platforms, assembled, and annotated. Analysis showed that the genome of Paraburkholderia does not differ greatly from free-living Burkholderiaceae, as it is not reduced and possesses a similar enzymatic potential. The genome of the fungal partner also seems similar to the genomes of its close relatives, however Umbelopsis belongs to a relatively understudied taxonomic group, thus conclusions about its genomic content are less certain. In the genomes we identified some features needed for establishment and maintenance of endohyphal interaction, such as genes coding for diacylglycerol kinase (DGK) and secretion systems. Finally, we detected potential metabolic intertwinement in wood degrading capacities of partners, which, combined with the detection of genes encoding plant growth promotion factors in bacteria, allows us to assume that the consortium is well adapted to develop in the decaying wood ecosystem from which it was isolated. Hence, it seems that although both partners can live independently, together they may occupy niches not available to each partner individually.