Research Article |
Corresponding author: Maxim S. Kulikovskiy ( max-kulikovsky@yandex.ru ) Academic editor: Kalina Manoylov
© 2021 Natalia D. Tseplik, Yevhen I. Maltsev, Anton M. Glushchenko, Irina V. Kuznetsova, Sergei I. Genkal, John Patrick Kociolek, Maxim S. Kulikovskiy.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Tseplik ND, Maltsev YI, Glushchenko AM, Kuznetsova IV, Genkal SI, Kociolek JP, Kulikovskiy MS (2021) Achnanthidium tinea sp. nov. – a new monoraphid diatom (Bacillariophyceae) species, described on the basis of molecular and morphological approaches. PhytoKeys 174: 147-163. https://doi.org/10.3897/phytokeys.174.60337
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A new monoraphid diatom species Achnanthidium tinea Tseplik, Kulikovskiy, Kociolek & Maltsev, sp. nov. is described from Indonesia. The species is described on the basis of molecular and morphological analyses. According to molecular data the new species belongs to the clade that includes strains of Achnanthidium minutissimum, Achnanthidium saprophilum and Achnanthidium digitatum. Morphologically, the new species differs quite significantly from other species of the same genus because of linear-elliptic valves with almost parallel sides and strongly radiate striae and a butterfly-shaped fascia on the raphe valve. The morphology and phylogeny of the new species are discussed, and thoughts on the current state of the taxonomy of the genus Achnanthidium are expressed. Our work shows the importance of using molecular data in diatom systematics and also demonstrates the need to investigate rarely studied regions of our planet.
Achnanthidium, Bacillariophyceae, Indonesia, molecular investigations, new species
The genus Achnanthidium Kützing was first described by
Recent studies include descriptions of many new species belonging to this genus (
Taxonomy within the genus Achnanthidium is a rather complicated issue. Species boundaries are often not clear enough due to the fact that morphological features alone may not be sufficient to unequivocally identify species, and because values of quantitative features often overlap in similar species, further complicating their separation (
Achnanthidium species are widely distributed in various freshwater habitats around the world and can be important indicators of environmental conditions (
The sample used in the present report was collected from Indonesia by I.I. Ivanov on 22.09.2010, and designated I227 from the Sulawesi Island, Temple Lake, periphyton, scraping from macrophytes, t=26.5 °C, pH=8.7, conductivity=277 μS cm-1, 04°06.923'N, 119°58.613'E.
Monoclonal strains were established by micropipetting single cells under an inverted microscope. Non-axenic unialgal cultures were maintained in WS liquid medium (
The sample and the monoclonal culture were treated with 10% hydrochloric acid to remove carbonates and washed several times with deionized water for 12 hours. Afterwards, the samples were boiled in concentrated hydrogen peroxide (≈37%) to dissolve organic matter. After decanting and refilling up to 100 ml with deionized water, the suspension was spread on to coverslips and left to dry at room temperature. Permanent diatom preparations were mounted in Naphrax (refraction index =1.73). Light microscopic (LM) observations were performed with a Zeiss Axio Scope A1 microscope equipped with an oil immersion objective (×100, n.a. 1.4, differential interference contrast) and Axiocam Erc 5s camera (Zeiss). Valve ultrastructure was examined using a JSM-6510LV scanning electron microscope (IBIW, Institute for Biology of Inland Waters RAS, Borok, Russia).
For scanning electron microscopy (SEM), parts of the suspensions were fixed on aluminum stubs after air-drying. The stubs were sputter-coated with 50 nm Au in an Eiko IB 3. Sample and slides are deposited in the collection of MHA, Main Botanical Garden Russian Academy of Science, Moscow, Russia. The type slide was designated 04133.
All images acquired from the slides were processed using Adobe Photoshop CC (19.0). Length and breadth of the valves were measured on the LM images, and striae and areolae density was measured on the SEM images. The numbers given in brackets in the description are means with standard deviations.
Total DNA of monoclonal cultures was extracted using InstaGene Matrix according to the manufacturer’s protocol. A fragment of 18S rDNA (382 bp, including V4 domain) was amplified using primers D512for and D978rev following
The resulting amplicons were visualized by horizontal agarose gel electrophoresis (1.5%), colored with SYBR Safe (Life Technologies, United States). Purification of DNA fragments was performed with the ExoSAP-IT kit (Affimetrix, USA) according to the manufacturer’s protocol. 18S rDNA fragment was decoded from two sides using forward and reverse PCR primers and the Big Dye system (Applied Biosystems, USA), followed by electrophoresis using a Genetic Analyzer 3500 sequencer (Applied Biosystems).
Editing and assembling of the consensus sequences were carried out by comparing the direct and reverse chromatograms using the Ridom TraceEdit program (ver. 1.1.0) and Mega7 (
The dataset was analyzed using the Bayesian inference (BI) method implemented in Beast ver. 1.10.1. (
Sample Ind296, isolated in sample I227.
Indonesia. Sulawesi Island, Temple Lake, periphyton, 04°06.923'N, 119°58.613'E, 5 m. elev., leg. I.I. Ivanov, 22.09.2010.
LM
(Fig.
SEM, external view
(Figs
A–D Achnanthidium tinea (Tseplik, Kulikovskiy, Kociolek & Maltsev), sp. nov. SEM. Sample no 04133. Raphe valves A–C external views D internal view A white arrows shows the central raphe ends. White arrowheads shows the distal raphe ends D white arrows shows the central raphe ends. White arrowheads shows the helictoglossae. Scale bars: 2 μm.
SEM, internal view
(Figs
Epithet refers to the butterfly-like shape of the fascia on the raphe valve of the new species; tinea meaning moth in Latin.
As yet known only from type locality.
Molecular data (Fig.
Our new species belongs to the large clade with monoraphid diatoms and sister clade with gomphocymbelloid diatoms. Strain A. tinea sp. nov. combined (BI 100; ML 100) with two strains of A. minutissimum AW2 and Ashort2 and A. saprophilum D06-036. 15 other strains of A. minutissimum combined to form a sister branch together with three strains of A. digitatum and A. gladius Tseplik et al. Other monoraphid taxa from genera Pauliella, Psammothidium, Planothidium, Cocconeis, Lemnicola and Gogorevia spp. formed sister clades to the branch containing these Achnanthidium taxa in the molecular tree.
Bayesian tree of Achnanthidium tinea (Tseplik, Kulikovskiy, Kociolek & Maltsev), sp. nov. (indicated in bold) constructed from a concatenated alignment of 152 partial 18S rDNA sequences of 404 characters. Values above the horizontal lines are bootstrap support from RAxML analyses (<50 are not shown); values below the horizontal lines and to the right of the slash mark are Bayesian posterior probabilities (<90 are not shown). All sequences have strain numbers (if available). Species of centric diatoms were used as an outgroup. * is 100% statistical support.
In terms of the data from both morphology and molecular sequence data, the new species A. tinea sp. nov. belongs to the genus Achnanthidium. Morphological features present in A. tinea and characteristic for this genus include: linear-elliptical valve shape, sternum that widens near the center of the valve and external distal raphe endings that are curved to one side. The last feature allows us to attribute the new species to the A. pyrenaicum species complex.
We compared A. tinea sp. nov. with other representatives of the genus Achnanthidium. A. tinea sp. nov. possesses a rather unusual combination of features for the genus: linear-elliptic valves with parallel sides and narrowed ends and a pronounced butterfly-shaped fascia on the raphe valve. After carrying out the morphological comparison, we identified several species most similar in morphology to A. tinea sp. nov. In terms of valve shape, the species most similar to the new species is Achnanthidium deflexum (Reimer) Kingston (
In general, due to the above-mentioned unusual combination of features possessed by the new species, its similarity with other representatives of the genus is mostly quite superficial, and A. tinea sp. nov. is easily distinguishable from other species even in light microscopy.
On the phylogenetic tree, the strain of A. tinea sp. nov. forms a separate branch within a clade that includes other species of Achnanthidium and other monoraphid diatoms (e.g. Gogorevia, Psammothidium, Planothidium, Pauliella, Cocconeis, Lemnicola) and the Cymbellales. The group was referred to as the Monoplacatae by
Our understanding of the phylogenetic relationships of the monoraphid diatoms continues to yield fascinating new insights at the levels of genus and species (e.g.
The authors are grateful to the staff of the Centre of Electron Microscopy of the Papanin’s Institute for Biology of Inland Waters, RAS, for technical assistance. Publication is based on research carried out with financial support by Russian Science Foundation (19–14–00320).
Taxa and DNA sequence data used in phylogenetic analysis
Data type: species data