Roholtiella Bohunická, Pietrasiak et Johansen, 2015

Bohunická, Markéta, Pietrasiak, Nicole, Johansen, Jeffrey R., Gómez, Esther Berrendero, Hauer, Tomáš, Gaysina, Lira A. & Lukešová, Alena, 2015, Roholtiella, gen. nov. (Nostocales, Cyanobacteria) - a tapering and branching cyanobacteria of the family Nostocaceae, Phytotaxa 197 (2), pp. 84-103 : 88

Roholtiella Bohunická, Pietrasiak et Johansen , gen. nov. ( Figs. 1–4 )

Morphologically similar to Calothrix , from which it differs by having chains of arthrospores and not tapering to a hair and by living in freshwater and soil habitats rather than marine or brackish waters. Morphologically and phylogenetically close to Calochaete , from which it differs by not having cell division in more than one plane and in the markedly different structure of all conserved regions of the 16S-23S ITS region.

Type species: — Roholtiella edaphica Bohunická & Lukešová spec. nov.

Description: —Thallus flat, spreading, usually growing into the substrate. Filaments short (from 8 cells) to very long, single false-branched, less often also double false-branched. Young filaments heteropolar, often with terminal heterocyte or isopolar, tapered towards both ends, soon breaking in the middle between two heterocytes and becoming heteropolar. Mature filaments heteropolar, with basal heterocytes and distinctly tapered apices. Sheath thin, attached, colorless in rapidly growing cultures; dense, delimited, colorless to reddish in older filaments. Trichome constricted at the crosswalls, tapering when young, less evidently tapering or untapered when mature. Cells cylindrical or barrel-shaped, usually isodiametric, in some species shortened and compressed near the base or immediately after cell division, often widened in the basal part of trichome and narrower near the apices. End cells usually conical or conical rounded, slightly elongated. Heterocytes form in pairs in intercalary position, becoming terminal through breakage between paired heterocytes, sometimes solitary in intercalary position and giving rise to single false branching, hemispherical, barrel shaped, or almost spherical, with one or two pores, yellow, pale yellow or tan colored. Arthrospores with thick cell wall, typically forming in series and released from the ends of the filaments by disintegration of the sheath. Hormogonia with cells of smaller dimensions and typically 10 (8–16) cells long, likely germinating from arthrospores, observed in all stages of the culture.

Notes: —Macroscopically, the thallus looks like Calothrix when young and like Nostoc when old (rugged crumbly surface), which is also in accordance with the microscopic appearance. Heterocytes are not formed in standard media with supplied nitrogen. Microscopically most similar to Calochaete cimrmanii , which differs in that cell division in two planes was observed in the original material ( Hauer et al. 2013, see fig. 1 L, M, O). In the description of C. cimrmanii , the authors stated that akinetes (called arthrospores in the Nostocaceae ) were not present ( Hauer et al. 2013). However, the authors show series of enlarged spherical cells at the trichome ends that bear some resemblance to the arthrospores of Roholtiella ( Hauer et al. 2013, see fig. 1 D, E, L), although they consider these series of enlarged cells to be hormogonia as they become detached and maintain their filamentous integrity. The 16S-23S ITS sequence of Calochaete is not easily aligned with those in Roholtiella , and the secondary structures of the three conserved helices are notably different.

Etymology: —Named in honor of the champion for wilderness areas in California, Christopher Roholt.

Figures

FIGURE 1. A–AB. Roholtiella edaphica, sp. nov. A–G. Hormogonia. H–I. Young tapered filaments with conical end cell. J–Q. Calothrix-like filaments with swollen base and basal heterocyte. J. Filament with intercalary heterocyte (marked with arrow). K, N–O. Filaments false branched at the heterocyte.R. Young filaments with isopolar growth. S–W. Mature filaments. S. Tapered mature filaments with brownish colored sheath, diffluent at the ends (marked with arrow). T–U. Single false branching. X–AB. Formation and releasing of arthrospores. Strains used in this figure: CCALA 1055 = I–J, Q, AB; CCALA 1056 = D–E, U–V, Y; CCALA 1060 = L, W; CCALA 1061 = A, H, R–T, Z; CCALA 1062 = B–C, F, M, O, X; CCALA 1063 = G, K, N, P, AA. Scale bar applies to all figures, in A–Q and S–AB = 20 μm, in R = 100 μm.

FIGURE 2. A–O. Roholtiella bashkiriorum, sp. nov. A. Hormogonium. B–E. Young tapered, Calothrix-like filaments. F. Branching at the heterocyte. I, K. Isopolar filaments with intercalary heterocyte(s), arrow marks a point of subsequent breakage. G–H, J, M–N. Mature filaments becoming arthrospores and being released from the opened ends. L, O. Rows of arthrospores.P–X.Roholtiella fluviatilis, sp. nov. P, S. Young tapered filaments. Q–X. Mature filaments and formation of arthrospores. R. Double false branching. U. Row of arthrospores. X. Filaments with reddish colored sheath. Strains used in this figure: CCALA 1057 = B–C, F, I–J, L, O, CCALA 1059 =A, D–E, G–H, K, M–N. CCALA 1058 = P–X. Scale bar applies to all figures, in A, B, D–H, J–P, R, T–X = 20 μm, in C, I, Q, S = 50 μm.

FIGURE 3. A–S. Roholtiella mojaviensis, sp. nov. A. Hormogonia. B–C. Maturing hormogonia. D–H, L–M. Tapered Calothrix-like filaments. E. False branching. H. Isopolar filament with two adjacent intercalary heterocytes, arrow marks a point of subsequent breakage. I–J. Mature filaments with near-spherical cells. K. False branching. N–Q. Rows of arthrospores. R. Releasing of arthrospores from the opened end of the filament. S. Mature tapered filament with thick structured colored sheath. Strains used in this figure: CCALA 1051 = A, D–I, K–O, Q–R, CCALA 1052 = B–C, J, P, S. Scale bar applies to all figures, in A–J and L–S = 20 μm, in K = 50 μm.

FIGURE 4. Ultrastructure of Roholtiella, strain CCALA 1061 R. edaphica in TEM. A–B. Cross-section of the vegetative cell. C. Longitudinal section of the filament surrounded by mucilaginous sheath, new cross-wall formation marked with arrow. D–E. Detail of the cell content and arrangement of thylakoids. F. Elongated cells in a young filament, longitudinal section. Cx = carboxyzome. Scale bars = 1 μm.