Chloroidium

Darienko, Tatyana, Lukešová, Alena & Pröschold, Thomas, 2018, The polyphasic approach revealed new species of Chloroidium (Trebouxiophyceae, Chlorophyta), Phytotaxa 372 (1), pp. 51-66 : 58

Chloroidium versus Parachloroidium

All investigated strains belonged to Chloroidium and Parachloroidium as demonstrated in Fig. 1 . The morphology of these strains was very similar and varied only in cell shape and size, chloroplast shape and the absence or presence of a pyrenoid ( Darienko et al., 2010, Neustupa et al., 2013b, Fig. 6 in this study). The distinction of both genera is very difficult because of lack of any synapomorphy in morphology and in SSU/ITS and rbc L sequences. The typically spherical cell shape of Parachloroidium could also be find in new isolates of Chloroidium . Neustupa et al. (2013b) described a genetic synapomorphy (insertion) at position 286 in the rbc L gene for Parachloroidium and Chloroidium . This synapomorphy could also be observed in the new taxa of Chloroidium . Neustupa et al. (2013b) used the codon AAG for the separation of Parachloroidium from Chloroidium (which has AAA in the insertion), coding for the inserted amino acid Lys. The strains MG-1 and MG-3 topologically closely related to both species of Parachloroidium , showed the same amino acid coding (AAA) and therefore represented genetic intermediates between Chloroidium and Parachloroidium . Considering both strains as new species of Parachloroidium , the genetic variability among the strains of Chloroidium and Parachloroidium was very similar, but was very low compared to other genera and species of the Watanabea clade. For example, both species of Kalinella differed by 152 and 12 bases in the SSU rDNA and rbc L sequences, respectively. Summarizing, Parachloroidium with the inclusion of the strains MG-1 and MG-3 does not show any morphological or molecular characters for recognition as separated genus. Therefore, as a result of our findings (no morphological differences, only a few genetic synapomorphies, low genetic variability), we transfer Parachloroidium and both of its described species to the emended genus Chloroidium (see below in taxonomic consequences and revisions).

Figures

FIGURE 1. Molecular phylogeny of Chloroidium based on SSU and ITS rDNA sequence comparisons. The phylogenetic trees shown were inferred using the maximum likelihood method based on the data sets (2643 aligned positions of 58 taxa) using PAUP 4.0b10. For the analyses the best model was calculated by Modeltest 3.7. The setting of the best model was given as follows: GTR+I+G (base frequencies: A 0.2263, C 0.2597, G 0.2814, T 0.2326; rate matrix A-C 3.0220, A-G 3.2461, A-U 1.8828, C-G 1.0985, C-U 7.0041, G-U 1.0000) with the proportion of invariable sites (I = 0.7069) and gamma shape parameter (G = 0.6406). The branches in bold are highly supported in all analyses (Bayesian values> 0.95 calculated with PHASE and MrBayes; bootstrap values> 70% calculated with PAUP using maximum likelihood, neighbor-joining, maximum parsimony and RAxML using maximum likelihood). The taxa originally described as Parachloroidium were indicated by an asterisk. The ITS-2 haplotype designations as well as the geographical origins and habitats are given color-coded after the strain designations.

FIGURE 6. Morphology and phenotypic plasticity of the new Chloroidium species. A.–G. C. antarcticum; H.–M. C. viscosum; N.–V. C. arboriculum; scale bar = 10 μm.