Vexillifera

Van Wichelen, Jeroen, D’Hondt, Sofie, Claeys, Myriam, Vyverman, Wim, Berney, Cédric, Bass, David & Vanormelingen, Pieter, 2016, A Hotspot of Amoebae Diversity: 8 New Naked Amoebae Associated with the Planktonic Bloom-forming Cyanobacterium Microcystis, Acta Protozoologica 55 (2), pp. 61-87 : 74

Vexillifera

The acanthopodial strain A18 WVB was placed in the monophyletic genus Vexillifera with V. multispinosa its closest relative ( Fig. 6A ), however the p -distance between these two strains was rather large (15.9%, 264 differing positions).

Locomotive amoebae of strain A18 WVB were highly variable. Their shape was either triangular, spherical, slightly elongated or irregular and pseudopodia were often dactylopodial-like (e.g. Figs 6B 3 , 7 ). Length without subpseudopodia was 13–43 µm (mean 22) and width 5–24 µm (11). About 9–22 (15) round-tipped subpseudopodia of maximally 11 µm long were present predominantly at the broader anterior side. A temporal, uroid-like, hyaline, bulbous or fasciculate structure (3–5 µm long) was sometimes seen posteriorly during locomotion (arrow in Fig. 6B 5 ). Usually one, rarely 2–3, small contractile vacuole(s) were visible posteriorly. The globular to elliptical vesicular nucleus was 2–5 µm in diameter and contained one slightly eccentrically located globular nucleolus of 1–2 µm. The cytoplasm always contained 10–40 small (1–2 µm), refractive spheroid granules. Floating amoebae ( Figs 6B 8 –11) were slightly elongated, about 15 µm long and 10 µm wide, displaying 5–17 sharply pointed pseudopodia that reached maximally 24 µm in length. No cyst stage was observed.

Vexillifera currently contains 24 species of which two were most probably misclassified ( V. expectata belongs to Hartmannella / Copromyxa and V. armata is probably Pseudoparamoeba pagei , see Dyková et al. 2011). Six of the remaining species were isolated from marine habitats, 1 from brackish waters and 4 from freshwater fish tissues (amphizoic species). The other species are all free-living amoebae from freshwater habitats, however none of these are represented in GenBank since it only contains the free-living marine species V. minutissima ( Bovee 1985) and the amphizoic Vexillifera species on fish ( Dyková et al. 2011). Our Microcystis -associated strain showed some morphological similarities with V. telma and V. displacata , described from eutrophied stagnant freshwaters respectively muddy bottoms of slow-running streams in the US ( Bovee 1985), however it differed in having an irregular floating form with long radiating pseudopodia (in contrast to the globular one of V. telma with only very small radiating pseudopodia), in being much larger (in contrast to V. displacata that is 7–12 µm long and 6–8 µm wide) and in its specific ecology (planktonic Microcystis colonies where it feeds on Microcystis cells and associated biota). These differences warranted its description as a new species, Vexillifera westveldii .

Figures

Fig. 6. A – 18S rDNA maximum likelihood phylogeny of Vexillifera, including the Microcystis-associated strain (in bold). ML bootstrap values respectively posterior probabilities are shown at the nodes. GenBank accession numbers are given together with the species names. B – LM pictures of locomotive (1–7, 12–13) and floating (8–11) amoebae. Microcystis cells inside food vacuoles are visible in (1–2) and (13). The arrow in (5) points to a temporal, uroid-like structure sometimes visible during locomotion. Scale bars: 20 µm.

Fig. 3. TEM pictures of the scales on the cell surface of Korotnevella jeppesenii (a, c) and K. pelagolacustris (b, d) trophozoites viewed from top (a, b) and side (c, d). Scale bars: 500 nm.

Fig. 7. A – 18S rDNA maximum likelihood phylogeny of Cochliopodium, including the Microcystis-associated strain (in bold). ML bootstrap values respectively posterior probabilities are shown at the nodes. GenBank accession numbers are given together with the species names. B – LM pictures of locomotive amoebae clearly showing the surrounding hyaline sheet (black arrows) punctuated with microscales (best visible in 8), a few small subpseudopodia (black arrowheads) and trailing adhesive uroidal filaments (white arrows) (1–5), a tropho- zoite during and just after grazing on Microcystis cells showing a prominent fringe of folded hyaloplasm (white arrowheads) (6–9), the bell-shaped form on colonies of Microcystis aeruginosa (10–11) and floating amoebae (12–13). Scale bars: 20 µm.

Fig. 5. LM pictures of Schoutedamoeba minuta showing trophozoites in non-oriented movement (a–f) and the limax-shaped locomotive form (g–i). The presence of a pronounced hyaline cap, small adhesive uroidal filaments and tiny granules in the cytoplasm are indicated with white arrowheads, black arrows and a white arrow respectively. Scale bars: 20 µm.

Fig. 8. A – 18S rDNA maximum likelihood phylogeny of Angulamoeba. Sequences new for this study are indicated in bold. ML bootstrap values respectively posterior probabilities are shown at the nodes. GenBank accession numbers are given together with the species names. B – LM pictures of Angulamoeba microcystivorans (strains A1WVB (1, 2, 4) and A4WVB (3)) showing the characteristic rusty-colored plasmodium-like mucilage matrix with embedded trophozoites devouring a culture of Microcystis aeruginosa colonies (1–2), multi-vacuolated trophozoites that are seemingly connected by their filopodia (3) and amoeba-flagellates in different stages of transition (4). Scale bars: 200 µm (1), 100 µm (2), 20 µm (3, 4).