Rhizobiales as functional and endosymbiontic members in the lichen symbiosis of Lobaria pulmonaria L.

Abstract

Rhizobiales (Alphaproteobacteria) are well-known beneficial partners in plant-microbe interactions. Less is known about the occurrence and function of Rhizobiales in the lichen symbiosis, although it has previously been shown that Alphaproteobacteria are the dominating group in growing lichen thalli. We have analyzed the taxonomic structure and assigned functions to Rhizobiales within a metagenomic dataset of the lung lichen Lobaria pulmonaria L. One third (32.2%) of the overall bacteria belong to the Rhizobiales, in particular to the families Methylobacteriaceae, Bradyrhizobiaceae, and Rhizobiaceae. About 20% of our metagenomic assignments could not be placed in any of the Rhizobiales lineages, which indicates a yet undescribed bacterial diversity. SEED-based functional analysis focused on Rhizobiales and revealed functions supporting the symbiosis, including auxin and vitamin production, nitrogen fixation and stress protection. We also have used a specifically developed probe to localize Rhizobiales by confocal laser scanning microscopy after fluorescence in situ hybridization (FISH-CLSM). Bacteria preferentially colonized fungal surfaces, but there is clear evidence that members of the Rhizobiales are able to intrude at varying depths into the interhyphal gelatinous matrix of the upper lichen cortical layer and that at least occasionally some bacteria also are capable to colonize the interior of the fungal hyphae. Interestingly, the gradual development of an endosymbiotic bacterial life was found for lichen- as well as for fungal- and plant-associated bacteria. The new tools to study Rhizobiales, FISH microscopy and comparative metagenomics, suggest a similar beneficial role for lichens than for plants and will help to better understand the Rhizobiales-host interaction and their biotechnological potential.

Differential sharing and distinct co‐occurrence networks among spatially close bacterial microbiota of bark, mosses and lichens‬‬

“…Previously, this order was linked to potential symbiotic functions, including provision of specific secondary metabolites and nutrient cycling in lichens (Erlacher et al . ; Grube et al . ).…”

“…Only Alphaproteobacteria form larger colonies on the lichen surfaces according to our previous FISH‐CLSM analyses of the lung lichen thalli (Erlacher et al . ; Grube et al . ), whereas diverse other eubacteria are present in rather scattered clusters (see also Fig.…”

Fine Spatial Scale Variation of Soil Microbial Communities under European Beech and Norway Spruce

“…In our study, more than one OTU determined at a genetic distance of 3% was affiliated to Pseudolabrys . The taxon Pseudolabrys , representing one of the most abundant genera detected in this study, belongs to the Rhizobiales, which are known to interact with plants (Erlacher et al, 2015). Changes in root densities or activities may be a major reason for high relative abundance of Pseudolabrys in soil located close to beech trunks.…”

Bacteria and Non-lichenized Fungi Within Biological Soil Crusts

“…Some observations of these microhabitats are presented in more detail below. While bacteria mostly colonize coherent surfaces of lichens and only few of them may penetrate more deeply (Erlacher et al 2015), lichenicolous fungi commonly invade the interior of their hosts with their filamentous hyphae to benefit from their symbiotic structures.…”