Fistulifera saprophila (Lange-Bert. & Bonik) Lange-Bertalot 1997

Novis, Phil M., Braidwood, Jasmine & Kilroy, Cathy, 2012, Small diatoms (Bacillariophyta) in cultures from the Styx River, New Zealand, including descriptions of three new species, Phytotaxa 64 (1), pp. 11-45 : 28-29

Fistulifera saprophila (Lange-Bert. & Bonik) Lange-Bertalot 1997 ( Figs 76–86 , 164 )

Frustules elliptical with rounded ends in valve view, 4.8–5.3 µm long, 2.7–3.1 µm wide, weakly silicified, biraphid. Living cells produce copious mucilage and contain 1–2 discoid parietal chloroplasts ( Fig. 76 ). Central sternum pronounced and more strongly silicified (clearly visible in LM of cleaned specimens), containing a single elongate stigma, laterally located towards the primary valve side, and longitudinally located between the central raphe termini. Raphe weakly undulate with slightly widened central termini and apical termini hooked towards the secondary valve side. Striae weakly radiate, (64–)68–72(–76) in 10 µm, with 1–4 shorter striae (that may alternate with longer striae) around the central area. Areolae very fine, round, located between sternum edge and approximately halfway to the valve margin, where they are replaced by transverse slits extending to the margin ( Figs 83–86 ). Striae not visible in LM. Girdle bands numerous and thin ( Fig. 83 ).

Reference: — Krammer & Lange-Bertalot (1986) p. 207, fig 74: 35, 36, fig. 75: 38; Lange-Bertalot (1997) p. 73, figs 28–32.

Specimens examined: —CHR618414! (cleaned frustules from cultured strain LCR-S:20:3)

Distribution: —regarded as cosmopolitan, but not previously known from New Zealand. It appeared in cultures from sites 4 and 7 in the Styx catchment.

Molecular data: —The closest matches to the rbc L sequence of the Styx strain were Fistulifera sp. JPCC DA0580, described as a marine diatom isolated from the junction of the Sumiyo and Yakugachi Rivers, Kagoshima, Japan ( Matsumoto et al. 2010; p-distance = 0.010) and Fistulifera pelliculosa (Bréb.) Lange- Bertalot 1997 CCMP 543, isolated from an oyster pond, Massachussetts, USA (p-distance = 0.012). These two strains formed a robust clade with the Styx strain in both Bayesian and MPB analyses, but relationships between the 3 taxa were unresolved ( Fig. 164 ). The length of the Styx fragment was 497 bp in a total dataset 1470 bp long, with 288 variable sites (170 parsimony informative, 57 occurring within the Styx fragment). The model chosen and implemented in the Bayesian analysis was GTR+G.

The closest matches to the 18S sequence of the Styx strain were Fistulifera saprophila clone NSAP2, isolated from the Benzelterbaach River, Luxembourg, and Naviculales sp. GSL083, isolated from Great Salt Lake, Utah, USA (both identical). The 18S sequence for Fistulifera pelliculosa strain HYNP021 differed substantially from these taxa (p-distance = 0.046), and examination of the alignment showed that it was distinctly different not only from the other strains of Fistulifera Lange-Bertalot 1997 but from all the other diatoms in this group. The Styx strain formed a robust clade with NSAP2 and GSL083 in both Bayesian and MPB analyses ( Fig. 164 ). The fragment from the Styx strain was 787 bp long, in an overall dataset of 1735 bp, with 171 variable sites (73 parsimony informative, 22 occurring within the Styx fragment). The model chosen and implemented in the Bayesian analysis was T92+G+I.

Observations: —The two described species of Fistulifera , F. saprophila and F. pelliculosa , are most easily distinguished by size. The Styx strain agrees well with published measurements of F. saprophila (4.5–7.6 µm long and 2–4µm wide, vs F. pelliculosa , 9–12.5 µm long and 4–6.2 µm wide, fide Krammer & Lange-Bertalot 1986). The species are very small and would be easily overlooked in LM, although once recognised it is unlikely to be confused with any other genus, due to its prominent sternum but otherwise light silicification, and very fine striae. Species of Fistulifera are evidently tolerant of a wide range of salinities, being found in fresh and brackish waters and in marine habitats elsewhere. Oceans are consequently unlikely to present a dispersal barrier; certainly there is little presently to distinguish the Styx strain from those isolated from other parts of the world. We note that one strain of Fistulifera is thought to have potential in biotechnology ( Matsumoto et al. 2010).

Figures

FIGURE 164. Bayesian phylogenies of Craticula and Fistulifera strains from the Styx River, for 18S rDNA (left) and rbcL (right). Support numbers above branches are Bayesian posterior probabilities / Maximum Parsimony bootstrap values. Scale bar = 0.1 subsitutions/site. See text for substitution models and description of data sets.

FIGURE 76–86. Fistulifera saprophila, strain LCR-S:20:3, CHR618414. Scales: Fig. 76, 5 µm (use for Figs 76–82); Fig. 84, 1 µm (use for Figs 83–86). Figs 76, 77. Live cells viewed by LM, showing lobed paretial plastid. Figs 78–82. Cleaned frustules viewed by LM, showing valve margin and thickened raphe/sternum. Figs 83–86. SEM of cleaned and partially cleaned valves (numerous thin copulae visible in Fig. 83).