Watanabea green microalgae (Trebouxiophyceae) inhabiting lichen holobiomes: Watanabea lichenicola sp. nova

Abstract

Microalgae of the genus Watanabea are widely distributed as free living in soil/subaerial and aquatic habitats. In this study, two Watanabea spp. were isolated from lichen thalli of Buellia zoharyi collected on biocrusts in the Iberian Peninsula and the Canary Islands. To ascertain their taxonomic position and phylogenetic relationships within the genus Watanabea, morphological observations were performed using light and confocal microscopy, combined with molecular analyses based on the phylogeny of small subunit ribosomal region (SSU) and internal transcribed spacer region (ITS) genes and the ITS2 secondary structure. One isolate matches Watanabea acidophila, and the other, which has not been previously reported, is described here as Watanabea lichenicola sp. nov. Both molecular phylogenetic analyses (SSU and ITS) suggest the division of the Watanabea spp. into two well-supported clades: Watanabea group I and Watanabea group II, to which W. lichenicola and W. acidophila belong, respectively. Furthermore, an exclusive side loop in helix 3 of the ITS2 secondary structure of Watanabea group II reinforces the use of this analysis as a molecular hallmark for this genus. The integrative approaches carried out in this study suggest lichen thalli as a new ecological niche for this genus, either as associated (not primary symbiont), epiphyte and/or endophyte microalgae in Buellia zoharyi holobionts.

Genomic analysis of Coccomyxa viridis, a common low-abundance alga associated with lichen symbioses

“…The lichen symbioses shown to contain C. viridis are quite diverse and the symbionts include representatives of both main groups of lichen photobionts (green algae and cyanobacteria) and several classes of mycobionts. Combined with reports of other non-photobiont algae frequent in lichens 12 , 15 , this finding raises questions about the place these algae occupy in the lichen symbiosis.…”

Genomic analysis ofCoccomyxa viridis, a common low-abundance alga associated with lichen symbioses

“…We detected C. viridis in one eighth of analyzed metagenomes. Combined with reports of other non-photobiont algae frequent in lichens [12,15], this finding raises questions about the place these algae occupy in the lichen symbiosis.…”

“…Coming from diverse groups and present in miniscule amounts, these 'additional' green algae have recently been termed the phycobiome [12] They are mostly detected in two ways. First, by culturing them from a lichen thallus (e.g., [13][14][15][16]). Sometimes this happens by accident, when researchers attempt to culture lichen photobionts [17].…”

Trebouxia lynnae sp. nov. (Former Trebouxia sp. TR9): Biology and Biogeography of an Epitome Lichen Symbiotic Microalga

“…Pure cultures of symbiotic algae are essential for species delimitation following an integrative taxonomic approach in which different analytical methods, combining morphology and genetic diversity, are considered [ 16 , 26 , 31 , 83 , 89 , 90 ]. Indeed, particularly for the genus Trebouxia , the lack of axenically cultured species has been, thus far, one of the major reasons for the unbalanced proportion between the genetically identified species-level lineages and the formally described species [ 5 , 6 , 15 , 16 ].…”