Trebouxia maresiae Garrido-Benavent, Chiva & Barreno, 2022

Garrido-Benavent, Isaac, Chiva, Salvador, Bordenave, César D., Molins, Arantzazu & Barreno, Eva, 2022, Trebouxia maresiae sp. nov. (Trebouxiophyceae, Chlorophyta), a new lichenized species of microalga found in coastal environments, Cryptogamie, Algologie 20 (9), pp. 135-145 : 139-143

Trebouxia maresiae Garrido-Benavent, Chiva & Barreno , sp. nov.

( Figs 1-3 )

Trebouxia maresiae Garrido-Benavent, Chiva & Barreno , sp. nov. shows crenulate chloroplasts that bear a crenulata-type pyrenoid when cells are in culture, whereas in the lichenized state it acquires a hybrid structure (maresiae-type), characterized by the periphery of the pyrenoid being rather gigantea-type, with thylakoid membranes forming short, branched tubules. These traits distinguish the new species from T. decolorans , which has deeply lobed chloroplasts with a decolorans-type pyrenoid. The two species also differ by the relatively high number of nucleotide differences in their nrITS DNA sequences. Vegetative cells of T. maresiae sp. nov. tend to be smaller in diameter (<15 µm) than those of other species in Trebouxia clade A like T. decolorans and T. solaris .

HOLOTYPE. — Spain. Balearic Islands, Mallorca, Es Trenc, phycobiont of Seirophora villosa (Ach.) Frödén collected on branches of Juniperus phoenicea subsp. turbinata (Guss.) Nyman in coastal dunes, 39°20’40.71”N, 2°59’8.24”E, 3 m a.s.l., 07.VIII.2008, leg. G. Salvà. The lichen specimen was deposited in the herbarium of the University of Valencia (VAL-Lich) with the following code: VAL-Lich 31798.

TYPE STRAIN. — Deposited at the Symbiotic Algal collection from the University of Valencia ( ASUV), as item type ASUV 142.

REFERENCE STRAINS. — ASUV 142 and ACOI 3420, deposited at the Coimbra Collection of Algae ( ACOI), University of Coimbra.

GENBANK ACCESSION NUMBERS. — MZ724411 (nrITS), MZ687825 (rbc L) and MZ687826 (COX2).

ETYMOLOGY. — According to the Canarian Academy of Language, the term “maresía”, from which the specific epithet “maresiae” derives, means “air laden with marine humidity in areas close to the seashore”. Therefore, this term refers to the particular habitat where the lichen phycobiont lives, in coastal sea-shore environments.

ECOLOGY. — In association with lichen-forming fungi of the genera Seirophora Poelt , Ramalina Ach. (this work), and Xanthoria parietina (L.) Th. Fr. (isolate no. P-280-II-a-Sc; Nyati et al. 2014).

DISTRIBUTION. — Currently, the known geographic distribution of the new alga includes the Mediterranean basin and the Cape Verdean Island of Santiago (this study; Nyati et al. 2014; Garrido- Benavent et al. 2022).

DESCRIPTION

Cells are mostly unicellular,rarely in tetrads and octads.Vegetative mature cells usually spherical, rarely oval, 7-11 (15) µm diam. Cell wall is usually thin and arranged in a bilayer. Chloroplast central, dissected into crenulated lobes with several tree-like lobes elongated at their ends. Some cells containing two chloroplasts may be also observed. The chloroplast usually contains a single pyrenoid of the crenulata-type with wide, branched tubules of curved profile, often crossing the entire pyrenoid. In symbiosis, however, the pyrenoid shows a hybrid structure (maresiae-type), characterized by displaying two discrete regions that can be each clearly assigned to different pyrenoid types; here, the pyrenoid periphery is more similar to the gigantea-type. Secondary pyrenoids may be present.Pyrenoglobuli present in the closest parts of the chloroplast stroma.The cytoplasm of old cells is sometimes yellowish, probably due to the presence carotenoid pigments, and vacuolated. Asexual reproduction involves the formation of autospores. Autosporangia (10-11 µm diam.) usually contain 4-16 (32) autospores. Sexual reproduction was not observed.

Figures

FIG. 1. — Phylogram showing the placement of the new species in a subclade of Trebouxia Puymaly clade A sensu Muggia et al. (2020). The phylogeny was built with MrBayes based on a three-locus dataset (nrITS, 5.8S and rbcL). For reference, green- and orange-filled boxes on the right of each tip indicate the species code of each Trebouxia species following Muggia et al. (2020). To the right, the voucher or culture collection code, as well as the name of the species, if any, are provided.Posterior Probabilities (PP) and bootstrap support values (BS, RAxML-NG analysis) are represented on branches leading to nodes on the left and right, respectively. Branches in bold had a significant statistical support (PP ≥ 0.95; BS ≥ 70%).

FIG. 2. — Habitat and morphology of Trebouxia maresiae Garrido-Benavent, Chiva & Barreno, sp. nov.: A, a thallus of the lichen Seirophora villosa (Ach.) FrÖdén from Es Trenc (Mallorca) with which this microalga associates;orange discs are apothecia produced by the lichen fungus to reproduce sexually;B-H, light microscopy photographs showing the gross morphology of vegetative cells and autosporangia; B, H, young and mature cells; C, central, crenulate chloroplast with a single pyrenoid; D, old cell with carotenoids in the cytoplasm; E-G, development of autosporangia and autospores; I-K, reconstruction of chloroplasts by LSCM; K, crenulate chloroplast with three pyrenoids (white arrowheads); L, reconstructed chloroplast of autospores within an autosporangium. Scale bars: 10 µm.

FIG. 3. — Ultrastructure of Trebouxia maresiae Garrido-Benavent, Chiva & Barreno, sp. nov. by TEM: A, B, cultured cells; C-F, cells within lichen thallus; F, detail of a pyrenoid. White arrowheads in D, E and F indicate the tubules in pyrenoid periphery that are more similar to these which characterize the gigantea-type pyrenoid. Abbreviations: Chl, chloroplast; CW, cell wall; Pg, pyrenoglobuli; Py, pyrenoid; Tu, tubules; Nu, nucleus; s, starch granules. Scale bars: 2 µm.