Complex and varying lichen microbiomes according to the vertical positions of thalli in Cladonia species from King George Island, Antarctica

Abstract

Lichens are symbiotic organisms that are majorly composed of lichenized fungi (mycobiont) and green algae/or cyanobacteria (photobiont). However, lichen thalli also contain highly diverse microbes such as bacteria, archaea and microfungi (microbionts) as well as mycobiont and photobiont. Although research interests on ecological functions of microionts have been raised greatly, very little knowledge on this topic has been gained, especially on microbionts of lichens from extreme environments. Microbial communities are usually affected by subtle changes of environments and different parts of lichen colonies, Cladonia gracilis, which forms lichen colonies composed of many slender individual thalli, may provide different micro-environments to the microbial communities of Cladoia gracilis from King George Island, Antarctica. To reveal the microbial communities of different parts of the lichenized fungi, we sectioned thalli from middle, intermediate, and marginal positions of colonies to apical, middle and basal parts. Since apical parts are usually more exposed to sun light and wind, and has lower humidity compared to basal parts, we considered this sectioning to represent different conditions. Bacterial 16S rRNA gene and eukaryotic nuclear large subunit rRNA gene (LSU) were analyzed by 454 pyrosequencing method. Alphaproteobacteria and Acidobacteria were the major bacterial phyla in all parts of the thalli with varying abundance. Apical parts of thallii contained relatively simple microbial communities that were majorly composed of Acetobacteriaceae and Acidobacteriaceae. Basal parts contained much more complex microbial communities with diverse phyla and enriched with Actinobacteria. LSU sequences were mostly composed of that of Cladonia gracilis, but also contained diverse fungal species including Lecanoromycetes, Leotiomycetes and Dithideomycetes with varying abundance depending on the vertical positions. High abundance of Ochrolechiaceae and Stereocaulaceae and diverse Cladonia genotypes in Cladonia gracilis thalli observed in this study may imply complicated life style of potentially lichenized fungi and complex composition of lichen thalli. Diverse algal species and different composition according to the vertical position provide insights on fungal selectivity to algal genotypes depending on the micro-environmental conditions.