Multiple Euryhaline Lineages of Centrohelids (Haptista: Centroplasthelida) in Inland Saline Waters Revealed with Metabarcoding

Abstract

The diversity of centrohelids in inland saline waters was studied with metabarcoding for the first time. The fragment of V6–V7 regions of 18S rDNA was sequenced with newly designed primers. Obtained OTUs were identified with molecular phylogenetic analysis and comparison of the signatures in 39es9 hairpin of V7. The obtained data included some OTUs, which could be attributed to four described species, but the majority belonged to previously established or novel environmental clades. Along with some presumably marine/brackish clades and freshwater/low salinity (0–2 ppt) clades, seven presumable species demonstrating broad (from 1–2 up to 78 ppt) salinity tolerance were detected. A number of OTUs belonged to Raphidocystis contractilis, which is known from three independent findings in brackish habitats only. Thus, it was assumed that this species is stenohaline and specifically adapted to salinity 5–15 ppt. The high level of salinity tolerance was suggested for centrohelids before based on morphology, which was used to justify their cosmopolitan distribution. Later these views were criticized based on environmental sequencing, but the results of the current survey indicate, that at least some species are present at salinities from almost freshwater (1–2 ppt) to twice oceanic (78 ppt) and are presumably capable of overcoming oceanic salinity barriers for their distribution.

Unexpected ubiquity of heart‐shaped scale morphotype in Centroplasthelida (Haptista): Ancestral trait or multiple acquisitions?

“…After 1 week of incubation of T‐9 clonal culture and growth of heliozoan population, cells were collected by tapering Pasteur pipette in a 1.5‐ml tube and frozen at −80°C for further DNA extraction. DNA from the clonal culture was isolated using phenol–chloroform extraction according to Gerasimova et al (2020). The quality of the extracted DNA was assessed with electrophoresis in 1% agarose gel and a Nanodrop 8000 (Thermo Fisher Scientific).…”

“…Centrohelids are characterized by ribbon‐shaped mitochondrial cristae, axopodia radiating from tripartite microtubules‐organizing centers (Cavalier‐Smith & Chao, 2012), and ball+cone element‐containing extrusomes (Sakaguchi et al, 2002). Centrohelid heliozoans inhabit benthos and periphyton of freshwater (Gerasimova & Plotnikov, 2016; Prokina & Mylnikov, 2019; Zlatogursky, 2013), marine (Prokina et al, 2019; Shɨshkin et al, 2018), and hypersaline ecosystems (Gerasimova et al, 2020; Plotnikov & Gerasimova, 2017), as well as soil (Cavalier‐Smith & von der Heyden, 2007; Zagumyonnyi et al, 2021). Centrohelid heliozoans along with haptophytes constitute the Haptista supergroup (Burki et al, 2016).…”

“…These species along with Choanocystis sp. AY749605 constitute the Ch1 clade (Gerasimova et al, 2020). In a recent paper, Shɨshkin‐Skarð et al (2022) pointed out that Penard's Choanocystis , initially described as desmothoracid, is not a centrohelid and hardly attributable to the further finding of “ Choanocystis lepidula ” by Siemensma and Roijackers.…”

Clypifer cribrifer gen. nov., sp. nov. (Clypiferidae fam. nov., Pterocystida, Centroplasthelida), with notes on evolution of centrohelid siliceous coverings

“…Centrohelids (Centroplasthelida Febvre-Chevalier and Febvre 1984 [1]) is a holophyletic ubiquitous group of unflagellated axopodial protists [2]. Centrohelids form a subclade of the clade Haptista sensu Cavalier-Smith 2003 [3].…”

Triangulopteris lacunata gen. et sp. nov. (Centroplasthelida), a New Centrohelid Heliozoan from Soil

“…However, most studies on centrohelid heliozoans are focused on ones found in freshwater. Specifically, reports on diversity and abundance of centrohelids from soil biotopes are handful [12,13]. Rather, soil biotopes were discarded as unsuitable habitats for centrohelids due to frequent changes in moisture level [1].…”