Morphology and phylogenetic position of a trebouxiophycean green alga (Chlorophyta) growing on the rubber tree,Hevea brasiliensis, with the description of a new genus and species

Abstract

A novel unicellular Chlorella-like green alga was isolated from the rubber tree (Hevea brasiliensis). The cultured cells were described by light and electron microscopy. Most adult cells were spherical with a single cup-shaped parietal chloroplast, although a few cells contained 2 to 4 chloroplasts. Chloroplasts contained many small pyrenoids with pyrenoglobuli around the multi-oriented tube-like thylakoids in the pyrenoid matrix. Most sporangia contained 2 or 4 autospores with a spindleshaped chloroplast. Phylogenetic analyses inferred from both chloroplast-encoded 16S and nuclear-encoded 18S rDNA sequences placed our isolate in the 'Chlorella' luteoviridis clade within the class Trebouxiophyceae. There are two group I introns in the 18S rDNA, structurally similar to 'Chlorella' trebouxioides, which also has two introns at the same positions. The exon sequence revealed highest similarities of 93-95% compared with 'C.' luteoviridis, 'Chlorella' saccharophila, and 'C.' trebouxioides. The chloroplast 16S rDNA has a unique 46-bp insertion in helix P21-1, which can be folded into a double hairpin structure. Blast searches resulted in best hits of 96% similarity to 'C.' luteoviridis (CCAP-211/3), and of 91% to 'C.' saccharophila (SAG 211-1d). Based on morphological features and phylogenetic position, a new genus Heveochlorella gen. nov. with the type species H. hainangensis sp. nov. is proposed.

Leptochlorella corticola gen. et sp. nov. and Kalinella apyrenoidosa sp. nov.: two novel Chlorella-like green microalgae (Trebouxiophyceae, Chlorophyta) from subaerial habitats

“…Members of the Heterochlorella lineage, including the genus Kalinella, are typified by unusually divergent 18S rRNA gene sequences (Krienitz et al, 2004;Zhang et al, 2008;Neustupa et al, 2009;Darienko et al, 2010;Aboal & Werner, 2011). The taxa within this clade formed long branches in phylogenetic reconstructions based on this marker, indicating an increased rate of evolution of the 18S rRNA gene in this lineage.…”

“…K. bambusicola was isolated from a tropical ecosystem and K. apyrenoidosa was found in a part of the Mediterranean with a humid subtropical climate, according to the Köppen-Geiger climate classification system (Peel et al, 2007). In addition, the phylogenetically closely related genera Heveochlorella and Phyllosiphon were also found in various subtropical or tropical subaerial localities (Zhang et al, 2008;Aboal & Werner, 2011). Therefore, we expect that additional taxa of the Heterochlorella lineage might be discovered in the little-known phototrophic microbial biofilms of these habitats.…”

“…They may also be found less frequently as lichen photobionts (Thüs et al, 2011) and a single species of this genus, Chloroidium saccharophilum, occurs in freshwater localities (Darienko et al, 2010). Further Chlorella-like taxa in the Watanabea clade include the genera Heterochlorella, Heveochlorella and Kalinella, typically encountered in corticolous subtropical to tropical habitats (Neustupa et al, 2009;Zhang et al, 2008). Interestingly, the profoundly morphologically different, epiphyllous and parasitic genus Phyllosiphon, which is characterized by a siphonous habit, was recently recovered in a sister position to the three corticolous genera mentioned above (Aboal & Werner, 2011).…”

Phylogeny and Molecular Evolution of the Green Algae

“…Although plastids are not apparent in Helicosporidium cells, molecular evidence indicates that it maintains a functional plastid genome (Tartar et al, 2003;de Koning & Keeling, 2004;Tartar & Boucias, 2004;de Koning & Keeling, 2006). Diversity and phylogenetic relationships within the Chlorellales have been well studied Krienitz et al, 2003;Henley et al, 2004;Zhang et al, 2008;Luo et al, 2010;Pazoutova et al, 2010;Pröschold et al, 2010). 18S and chloroplast genome data provided evidence that the Oocystaceae, including the semi-colonial Oocystis and the spiny Lagerheimia, form an early diverging clade within the Chlorellales (Hepperle et al, 2000;Krienitz et al, 2003;Turmel et al, 2009b).…”

“…Several distinct lineages within the Trebouxiophyceae have been recovered by molecular data, including the Chlorellales, Trebouxiales, Microthamniales, Prasiola-clade and several clades that have not yet received a formal name (Katana et al, 2001;Friedl & O'Kelly, 2002;Krienitz et al, 2003;Zhang et al, 2008;Neustupa et al, 2011). Resolving the branching patterns among these lineages can provide important insights into morphological and ecological evolution, and provide clues about the origins and adaptations of symbiotic and parasitic lifestyles, ultimately leading to obligate heterotrophic lifestyles.…”