Core taxa and photobiont-microbial interaction within the lichen Heterodermia obscurata (Physcsiaceae, Heterodermia)

The dual nature of fungal-algal lichen symbioses is extended by other microbial associations. Increasing evidence has confirmed that lichens are successful holobionts composed of complex and multiple species. Specific interactions between these microbes contributed to the lichens’ health, growth and fitness. Previous studies suggested that the composition of microorganisms in lichens was potentially influenced by the genetic background of the host-symbiont, large-scale geography or different photobiont-types (cyanobiont and chlorobiont). However, our knowledge of the interactions between the main symbiotic partners under a certain ecological condition and how horizontal acquisition of these microorganisms contributes to endolichenic microbiome diversity remains limited. In the present study, using amplicon sequencing, we investigated the complex diversity and community composition of fungi, bacteria, and microalgae within Heterodermia obscurata from a similar niche. We found that endophytic bacteria displayed greater diversity than fungi and microalgae. Although preferences for core taxa varied among the different definitions, all analyses support that lichen-forming genus Heterodermia and green alga Trebouxia sp. OTU A15 were the main symbionts, and the bacterium Beijerinckiaceae was the core microbiome in H. obscurata . Significantly, we found that different alga species ( Trebouxia ) from H. obscurata are accompanying with a shift in composition and function of endolichenic bacteria and fungi. This finding suggested that besides host- or habitat specificity as well as photobiont-types, the shifts of dominant alga may also contribute to the taxonomical and functional differences of microbiomes within lichens.