In silico search reveals the association of lichens with black yeast-like fungi in the order Chaetothyriales

Abstract

Lichens exemplify a unique symbiotic relationship between fungi and algae or cyanobacteria, where fungi (mycobionts) provide structural support, while algae or cyanobacteria (photobionts) provide nutrients. Recent discoveries in the order Chaetothyriales have led to the description of several lichenicolous species, underscoring an intricate relationship of some black yeast-like fungi with lichens. The present study aims to investigate public metagenomic data of lichens available in the SRA database, covering a total of 2888 samples. The analysis incorporated 122 molecular marker sequences (barcodes and padlock probes) previously documented in the literature for species classified within Chaetothyriales. Additionally, 11 novel barcodes for species recently identified in lichens of the genera Cladophialophora and Paracladophialophora are described. The selected metagenomes were then compared with molecular marker sequences using local BLASTn (v2.6.0+), considering only alignments with a coverage cut-off and 100 % identity (perfect match). Reads from each sample were retrieved from the SRA as a multifasta file and analyzed with the SWeeP method for vector-based, alignment-free sequence analysis. The analysis identified fungi that are known as environmental inhabitants and, occasionally, opportunistic pathogens of vertebrates, including species in the genera Cladophialophora, Cyphellophora, and Exophiala. These species were distributed across 11 BioProjects from various locations around the world. The findings of this study corroborate extant knowledge concerning fungal colonization in diverse extremophilic environments, including deserts, tundra, and rocky surfaces.