The green algal genus Trebouxia Puymaly is among the most widespread phycobionts, associating with a broad range of lichen-forming fungi. To date, around 30 Trebouxia spp. have been described based on the combination of morphological traits and genetic diversity. However, due to the limited number of morphological characters and the general lack of Trebouxia strains isolated in culture, a clear characterization of the species base on morphological and ultrastructural traits still remain challenging in this lichen-forming microalgae. In this work we used transmission electron microscopy (TEM) to characterize the ultrastructure of Trebouxia pyrenoids and laser scanning confocal microscopy (LSCM) to characterize the morphology of Trebouxia chloroplasts. 20 Trebouxia strains, grown in cultures directly on solid agar medium or on cellulose-acetate discs laid over the agar medium, were included in this analysis. Our results evidenced that Trebouxia pyrenoid and chloroplast diversity is higher than it was previously reported in literature. In addition, the studied algae maintain similar ultrastructure and morphology when grown either on agar medium or acetate discs. Analysing the ultrastructural and morphological traits of the pyrenoid and chloroplast in the light of the most updated Trebouxia phylogeny, we were able to reappraise and clarify the classification of the pyrenoids and chloroplasts within this genus. This work is intended to be the stepping-stone for future research when isolated Trebouxia species are identified by means of microscopy and molecular characters.
Funding: Generalitat Valenciana, GVA Excellence in Research (PROMETEO III /2017/039).
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