Phormidium autumnale (Agardh) Trevisan ex Gomont

Novis, Phil M. & Visnovsky, Gabriel, 2011, Novel alpine algae from New Zealand: Cyanobacteria, Phytotaxa 22 (1), pp. 1-24 : 20-22

Phormidium autumnale (Agardh) Trevisan ex Gomont ( Figs 8A–Q )

Trichomes uniseriate, cells (4–) 5–6 µm wide, 3–7 µm long, shorter than wide to approximately isodiametric, constricted at transverse walls, bright blue-green. Motile by slow gliding. Trichomes straight to slightly curved, except at terminus, where first 5–18 cells are tapered (down to 3–4 µm wide), straight to strongly curved or S-shaped ( Figs 8A–G ). Terminal cell rounded, with prominent rounded calyptra. Sheath thin and translucent. Branching absent. Trichome reproduction through fragmentation into hormogonia, sometimes at regions of variable trichome width ( Figs 8M–O ). Thylakoids peripheral but irregularly arranged ( Fig. 8Q ).

Habitat:— Alpine herbfield soil, 1640 m, associated with scattered Chionochloa sp.

Distribution:— The species is reported world-wide ( Komárek & Anagnostidis 2005); another strain found in the Hutt River, Wellington region, New Zealand, is likely identical to our strain (see below).

Observations:— Our observations agree well with the strict concept ( Komárek & Anagnostidis 2005) of this very widely reported species. Some minor differences are that our material has not been observed to rotate or oscillate while gliding, and is more often curved, especially in the attenuated region at the terminus.

Nonetheless 16S rDNA data show that this strain is placed in a clade of taxa regarded as P. autumnale , containing the majority of strains by that name ( Fig. 3 ; Palinska & Marquardt 2008). Other New Zealand strains have been sequenced and assigned to this species previously, though not from the alpine zone: in fact one such strain (VUW9, from the Hutt River; Heath et al. 2010) shares an identical 16S rDNA sequence for the 354 sites at which the two overlap, and seems likely to be identical overall. The 16S–23S intergenic spacer region of our strain contains both tRNA-Ile and tRNA-Ala genes ( Table 8), which is the case for all other strains of P. autumnale except one (UTEX 1580) where this region has been characterised.

Culture:— LCR-OSC3.

Figures

FIGURE 3. Phylogenetic analysis of selected Oscillatoriales inferred from 16S 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); these are shown only when PP> 0.94. Scale bar represents 0.1 changes per site.

FIGURE 8. Phormidium autumnale (Agardh) Trevisan ex Gomont (photographed from culture LCR-OSC3). A–P light micrographs, Q transmission electron micrograph. A–G. Terminal region of trichomes, showing distinct tapering, variation in shape from strain to curved or S-shaped, and presence of calyptra (indicated by arrow in A). H. Cylindrical region of trichome; division planes of cells that are currently dividing are indicated by arrows. I. Trichomes may be closely appressed, but do not share a sheath. J. Trichomes are usually slightly curved rather than straight as in H. K. Recently fragmented trichomes have rounded terminal cells. L. Cells within trichomes may vary in width. M. Trichome fragmentation in a region of cells with equal width. N. Fragmentation in a region of cells with varying width. O. Release of hormogone as a result of necridic cell formation (nc). P. Hormogone development is isopolar. Q. Cell in transverse section showing sheath (s) and peripheral thylakoids (tm), that have an irregular orientation in the cytoplasm. Scales: 10 µm in B (use in A–P), 1 µm in Q.