DOI: 10.5061/dryad.mw6m90667
title: A thallus forming N-fixing fungus-cyanobacterium symbiosis from subtropical forests

description: Fungi engage in diverse symbiotic relationships with phototrophs. Lichens,
 symbioticcomplexes involving fungi and either cyanobacteria, green algae,
 or both, have fungi forming the external layer and much of the interior.
 We discovered an erect thallus resembling a lichen, yet with a surprising
 thallus structure composed of interwoven cyanobacterial filaments with
 numerous fungal hyphae inserted within individual cyanobacterial sheaths,
 contrasting with typical lichen structure. Phylogenetics identified the
 fungus as a previously undescribed species, Serendipita cyanobacteriicola,
 closely related to endophytes, and the cyanobacterium belongs to the
 family Coleofasciculaceae, representing a genus and species not yet
 classified, Symbiothallus taiwanensis. These thalli exhibit N-fixing
 activity similar to mosses but lower than cyanolichens. Both symbiotic
 partners are distinct from known lichen-forming symbionts, uncovering a
 phylogenetically and morphologically unprecedented thallus-forming
 fungus-cyanobacterium symbiosis. We propose the name “phyllosymbia” for
 these thalli, to underscore their unique symbiotic nature and leaf-like
 appearance. This finding marks a previously unknown instance of
 fungi solely residing within structures generated by cyanobacteria.
description: We utilized the ITS+28S rRNA dataset to reconstruct the fungal
 phylogenetic tree. Species and samples for the ITS+28S dataset were
 selected based on recent studies. Sequence alignment was performed using
 MAFFT v.7 (https://mafft.cbrc.jp/). For the bacterial phylogenetic tree, we used a second dataset consisting of 16S rRNA gene sequences. The selection of 16S sequences was informed by Cydrasil (https://www.cydrasil.org/) and recent studies. Phylogenetic analyses, including Bayesian inference (BI) and maximum likelihood (ML), were conducted using MrBayes 3.2.7a and RAxML-HPC 8.2.12 via the CIPRES Science Gateway (http://www.phylo.org/). Evolutionary models for each gene region of both datasets were predicted using jModelTest2 2.1.6, based on the Akaike information criterion (AIC). The BI analyses were run for 10 million generations with four chains, sampling every 1000 generations. The initial 25% of trees were discarded as burn-in, and the remaining trees were used to generate the 50% majority-rule consensus phylogram with Bayesian posterior probabilities (BPPs). ML analyses were performed under a GTRCAT model with 1000 bootstrap replicates, resulting in a best-scoring tree with proportional bootstrap values (BS). Phylograms were visualized and edited using the Interactive Tree of Life (iTOL) (https://itol.embl.de/) and Adobe Illustrator. BS ≥ 70 and BPPs ≥ 0.9 were reported above the branches of the phylogenetic tree.
description: # Novel fungus-cyanobacterium symbiosis revealed in subtropical montane
 cloud forests
 [https://doi.org/10.5061/dryad.mw6m90667](https://doi.org/10.5061/dryad.mw6m90667) ## Description of the data and file structure Phylogenetic trees in NEXUS format and sequence alignments in FASTA format. ### Files and variables #### File: Fig.\_4\_Bacteria\_16S\_alignment.fas **Description:** 16S sequence alignment used to reconstruct the bacterial phylogenetic tree in Fig. 4, including 44 samples and 1530 characters with gaps. #### File: Fig.\_4\_Bacteria\_16S\_phylogenetic\_tree\_Bayesian\_inference.nex **Description:** Bacterial phylogenetic tree in Fig. 4 reconstructed from 16S sequence data using Bayesian inference method. #### File: Fig.\_4\_Fungi\_ITS\_28S\_phylogenetic\_tree\_Bayesian\_inference.nex **Description:** Fungal phylogenetic tree in Fig. 4 reconstructed from ITS+28S sequence data using Bayesian inference method. #### File: Fig.\_4\_Fungi\_ITS\_28S\_alignment.fas **Description:** ITS+28S sequence alignment used to reconstruct the fungal phylogenetic tree in Fig. 4, including 43 samples and 1634 characters with gaps. #### File: Fig.\_S5\_Fungi\_ITS\_28S\_phylogenetic\_tree\_maximum\_likelihood.nex **Description:** Fungal phylogenetic tree in Fig. S5 reconstructed from ITS+28S sequence data using the maximum likelihood method. #### File: Fig.\_S6\_Bacteria\_16S\_phylogenetic\_tree\_Bayesian\_inference.nex **Description:** Bacterial phylogenetic tree in Fig. S6 reconstructed from 16S sequence data using Bayesian inference method. #### File: Fig.\_S5\_Fungi\_ITS\_28S\_alignment.fas **Description:** ITS+28S sequence alignment used to reconstruct the fungal phylogenetic tree in Fig. S5, including 103 samples and 1668 characters with gaps. #### File: Fig.\_S6\_Bacteria\_16S\_alignment.fas **Description:** 16S sequence alignment used to reconstruct the bacterial phylogenetic tree in Fig. S6, including 91 samples and 1506 characters with gaps.