Bracteacoccus ruber Novis & Visnovsky, 2012

Novis, Phil M. & Visnovsky, Gabriel, 2012, Novel alpine algae from New Zealand: Chlorophyta, Phytotaxa 39, pp. 1-30 : 16

Bracteacoccus ruber Novis & Visnovsky , sp. nov. ( Figs 2A–G )

Cellulae sphaericae, 5.0–24.0(–60.0) µm latae, unicae vel in greges laxos irregulars aggregatae. Paries cellularis laevis, in cellulis immaturis <0.5 µm crassus, sed in cellulis maturis magnis usque ad 5.0 µm crassus. Chloroplasti numerosi discoideo–polygonii pyrenoidibus carentes, parietales sed interdum ad interioribus cellulae plicati. Autosporis 2–4–8–16 per sporangium regenerans. Cellulae in culturis vetustioribus in cytoplasmate praecipue quum luci valda objectata pigmentationem evolventes, imprimis in area nucleum proxime ambiente.

Type:— NEW ZEALAND: Westland : Mt Philistine, 1400 m, preserved cultured specimen from sample collected 30 November 2007, CHR610485 .

Cells spherical, 5.0–24.0(–60.0) µm wide, single or in loose, irregular groups. Cell wall smooth, <0.5 µm thick in young cells, but up to 5.0 µm thick in large, mature cells ( Fig. 2C ). Numerous discoidal–polygonal chloroplasts lacking pyrenoids, parietal but occasionally folded towards the cell interior ( Fig. 2A ). Reproduction through autospores, 2–4–8–16 per sporangium ( Fig. 2D ). Zoospores not observed. Cells in older cultures develop red pigmentation in the cytoplasm, especially immediately surrounding the nucleus and when exposed to strong light (compare Figs 2F and G ). DNA sequence data for 18 S showed the species to belong to Bracteacoccus , but without close affinities ( Fig. 7 ).

Habitat:— Alpine herbfield soil.

Distribution:— New Zealand.

Etymology:— Referring to the red pigmentation developed by older cultures.

Observations:— Data for rbc L failed to reconstruct Bracteacoccus as a clade ( Fig. 9 ); the phylogenetic conclusions are therefore drawn from 18S data. The size and red colouration of B. ruber resemble those reported for B. minor (Chodat) Petrová 1931 , but the two are not closest relatives according to DNA sequences. Fučíková et al. (2011) suggest that Bracteacoccus ( Tereg 1923) and Pseudomuriella ( Hanagata 1998) are morphologically cryptic genera. However, our strain of Bracteacoccus is clearly related to B. aerius ( Bischoff & Bold 1963) UTEX 1250 , which falls in the Bracteacoccus clade of Fučíková et al. The large cells with multilayered wall suggest B. giganteus ( Bischoff & Bold 1963) , but 18S rDNA sequences clearly distinguish this from B. ruber ( Fig. 7 ).

Capacity to develop the red colouration was found to diminish over time following isolation from field material, especially if the population underwent a culture cycle in liquid medium before replating on agar. A crude spectrophotometer test indicated that the pigment absorbs in the UV spectrum (data not shown).

Cultures:— LCR-CG8.

Figures

FIGURE 2. Bracteacoccus ruber (photographed from culture LCR-CG8). A–D, F, G light micrographs, E transmission electron micrograph. A. Cells in exponential growth phase, showing range of sizes from new autospores (a) to mature cells (m). Note occasional infolding (i) of chloroplasts towards cell interior. B. Typical mature cells in older cultures. C. Rare giant cell in an older culture, with thick lamellated wall (lm). D. Autosporangium in older culture. E. Young cell viewed with transmission electron microscope, showing parietal chloroplast (pc) containing starch (st) and vesicles (v) containing pigment. F. Typical cells grown at low irradiance in agarised culture. G.Typical cells grown at higher irradiance, showing larger size, thicker walls, and distinct pigmentation (the pigment is red when seen in colour). Scales: 10 µm in B (use B for A–D) and F (use F for F and G) and 1 µm in E.

FIGURE 7. Phylogenetic analysis of the Chlorophyceae inferred from 18S rDNA sequences. Sequences contributed in this study are in bold. The tree typology is that inferred using MrBayes v3.0B4 (5 million generations). Numbers associated with nodes are Bayesian PP/MPB percentages (500 replicates). Scale bar represents 0.1 changes/site.

FIGURE 9. Phylogenetic analysis of a combined dataset representing the Chlorophyceae and Trebouxiophyceae inferred from rbcL gene sequences, with the third codon position omitted. Sequences contributed in this study are in bold. The tree typology is that inferred using MrBayes v3.0B4 (5 million generations). Numbers associated with nodes are Bayesian PP/MPB percentages (500 replicates). Scale bar represents 0.1 changes/site.