Vulcanochloris Vančurová, Peksa, Němcová et Škaloud, 2015
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publication ID |
https://doi.org/ 10.11646/phytotaxa.219.2.2 |
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persistent identifier |
https://treatment.plazi.org/id/03C4F262-FFB1-BD11-FF1F-FCF6E50B3304 |
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treatment provided by |
Felipe |
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scientific name |
Vulcanochloris Vančurová, Peksa, Němcová et Škaloud |
| status |
gen. nov. |
Vulcanochloris Vančurová, Peksa, Němcová et Škaloud , gen. nov.
Vegetative cells spherical, rarely oval or oviform. Cell wall thin, seldom a flat local thickening of the cell wall can be observed. Rarely, the cell wall is slightly thickened along its entire surface. Cells contain a single asteroid chloroplast, with a distinct pyrenoid in its centre. The pyrenoid often contains one to several spherical incisions. Prior to aplano- and zoosporogenesis, the chloroplast flattens and assumes a parietal position. Asexual reproduction by 16–128 aplanospores or 64–128 zoospores. Zoospores naked, with two apical flagella and a simple basal chloroplast; stigma not observed. Mature aplanospores and zoospores liberated by rupturing of the mother cell wall. Lichen photobiont, so far found only in thalli of Stereocaulon vesuvianum . Morphologically similar to Asterochloris , from which it differs by the presence of spherical incisions in the pyrenoid matrix.
Type species:— Vulcanochloris canariensis , sp. nov. (see below)
Etymology:—From “Vulcanus” (L), Roman god of fire, and “chloris” (Gr.), meaning greenish-yellow. The name indicates that this algal genus was originally reported from a volcanic substrate.
Chloroplast morphology and ultrastructure:—The chloroplast is centrally located, axial, with variously arranged lobes reaching the cell periphery. Several chloroplast types can be recognized, as follows: i) a deeply lobed type, characterized by long lobes emerging directly from the thin chloroplast layer spreading around the pyrenoid (“Tieflappig Typ” sensu Gärtner 1985b; Figs. 1A, B View FIGURE 1 ); ii) a shallowly lobed type, which is similar to the previous type but differs in that the chloroplast lobes are shorter, emerging from the central mass of the chloroplast layer (“Normaltyp” sensu Gärtner 1985b; Figs. 1C, D View FIGURE 1 ); iii) a crenulate type, characterized by a central, massive chloroplast with a regularly nodulated surface (“Crenulater Typ” sensu Gärtner 1985a; Figs. 1E, F View FIGURE 1 ); and vi) an echinate type, distinguished by numerous thin radial lobes emerging uniformly from the central mass of the chloroplast layer ( Figs. 1G, H View FIGURE 1 ). In the late ontogenetic stages, specifically prior to zoo- or aplanosporogenesis, the chloroplast transforms into the parietal type, with smooth, never lobed margins, which is followed by its division into numerous parts in preparation for asexual reproduction ( Fig. 1I View FIGURE 1 ).
Large, distinct pyrenoid lies in the chloroplast centre ( Figs. 1A, C, E, G View FIGURE 1 ). The pyrenoid is usually spherical, rarely irregularly elongated, surrounded by a high number of small starch grains ( Figs. 1C, J View FIGURE 1 ). The pyrenoid is irregularly transversed by inclusions bearing a close structural resemblance to the chloroplast thylakoids ( Figs. 1K, M View FIGURE 1 ). In some cases, the incisions are clearly lined by membranes ( Figs. 1K, M View FIGURE 1 ). No pyrenoglobuli are associated with the thylakoidlike inclusions in the centre of the pyrenoid matrix. Instead, they are developed at the pyrenoid periphery ( Figs. 1K, M View FIGURE 1 ). One to several electron-lucent, spherical to elongated regions are frequently formed within the pyrenoid matrix ( Figs. 1N, O View FIGURE 1 ). Rarely, these regions may be associated with several pyrenoglobuli ( Fig. 1N View FIGURE 1 ). Occasionally, a higher number (more than 8) of these electron-lucent regions are formed within the pyrenoid matrix ( Fig. 1P View FIGURE 1 ). These regions probably correspond to spherical pyrenoid incisions observed in a light microscope ( Figs. 1E, G, J View FIGURE 1 ).
Molecular analyses:—To evaluate both the phylogenetic position and genetic diversity of Vulcanochloris , we sequenced rbcL gene, 18S rDNA and ITS rDNA spacer for several isolates. The rbcL data set consists of 70 Trebouxiophycean taxa, with 1139 characters. All phylogenetic analyses (BI, ML, MP) resolved Vulcanochloris as a distinct clade within Trebouxiales , with full statistical support ( Fig. 2 View FIGURE 2 ). In addition, sister position of genera Vulcanochloris and Asterochloris was highly supported, as well, with a moderate to very strong support for the monophyly of the latter genus. To further evaluate the reciprocal monophyly of Vulcanochloris and Asterochloris , we performed several Shimodaira-Hasegawa nonparametric tests (SH tests) comparing the best tree with four optimal trees constrained for Asterochloris paraphyly. The four topological constraints each represented one of the paraphyletic trees obtained by the ML botstrapping, as follows: i) monophyly of Vulcanochloris , A. erici , A. magna and A. phycobiontica , ii) monophyly of Vulcanochloris , A. erici and A. phycobiontica , iii) monophyly of Vulcanochloris and A. erici , iv) monophyly of Vulcanochloris , A. erici and A. magna . Tree comparisons indicated that paraphyly of Asterochloris was a significantly worse interpretation of these data (p <0.001, -ln for monophyly: 22,873.5, -ln for paraphyly: i) 22,905.5, ii) 22,902.9, iii) 22,893.4, iv) 22,893.4), supporting the reciprocal monophyly of genera Asterochloris and Vulcanochloris .
18S rDNA data set consisted of 37 sequences with 1776 characters, including three newly obtained Vulcanochloris sequences. Bayesian inference of the 18S rDNA and rbcL data yielded similar tree topologies, resolving Vulcanochloris , Asterochloris , Trebouxia , and Myrmecia as well-defined, distinct genera. In the 18S rDNA analysis (see Supplementary File 1), a clade of environmental sequences from soil samples ( Lesaulnier et al. 2008) was additionally inferred. Comparison with other 18S rDNA sequences showed that six Asterochloris strains and two Vulcanochloris samples (A104, L1618) contained IB3 group I introns at position 516 relative to the E. coli coding region. The exon SSU rDNA sequences of samples A104 and L1618 were completely identical.
ITS rDNA data set consisted of 31 sequences with 502 characters, including 15 newly obtained Vulcanochloris sequences, 13 Asterochloris sequences selected to encompass the entire diversity of this genus, and 3 additional sequences retrieved by BLAST searches at NCBI. The BI, ML, and MP phylogenetic analyses inferred from the ITS rDNA sequences resulted in highly similar phylogenetic trees, recognizing Asterochloris and Vulcanochloris as two distinct lineages, with full statistical support ( Fig. 3 View FIGURE 3 ). Newly obtained Vulcanochloris sequences formed three distinct lineages, here referred to as V. symbiotica sp. nov., V. canariensis sp. nov., and V. guanchorum sp. nov. V. symbiotica represents the most common lineage, containing 80% of all investigated isolates. This species was detected in all investigated localities. The second lineage, V. canariensis , consisted of two, genetically distinct isolates, A98 and L1620. The third lineage consisted of V. guanchorum isolate A104, and genetically identical sequence deposited in GenBank as “ Chlorophyta sp. URa22” (KF907692). Finally, two additional sequences retrieved from GenBank as “ Asterochloris sp. URa17” (KF907645, KF907671) were found to be members of the genus Vulcanochloris . However, their phylogenetic position, as well as the relationship among the three Vulcanochloris lineages, remain unresolved, though the rbcL and SSU rDNA phylogenetic analyses point to the close relationship of V. guanchorum and V. symbiotica .
Above-mentioned genetic investigation, as well as detailed morphological analyses of all the studied Vulcanochloris strains, revealed the existence of three distinct species. Descriptions of these new taxa are provided below.
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