Halocafeteria seosinensis gen. et sp. nov. (Bicosoecida), a halophilic bacterivorous nanoflagellate isolated from a solar saltern

Abstract

Recently, heterotrophic nanoflagellates (HNF) have been reported to actively ingest prokaryotes in high salinity waters. We report the isolation and culture of an HNF from a Korean saltern pond of 300 per thousand salinity. The organism is biflagellated with an acronematic anterior flagellum and never glides on surfaces. The mitochondria have tubular cristae. Neither transitional helix nor spiral fiber were observed in the transition zones of the flagella. The cell has a cytostome supported by an arc of eight microtubules, suggesting that our isolate is a bicosoecid. Our isolate had neither mastigonemes, lorica, body scales, nor cytopharynx and thus could not be placed in any of the presently described bicosoecid genera. Phylogenetic analysis of 18S rRNA gene sequences from stramenopiles confirmed the bicosoecid affinities of our isolate, but did not place it within any established genus or family. Its closest relatives include Caecitellus and Cafeteria. The optimal range of growth temperature was 30-35 degrees C. The isolated HNF grew optimally at 150 per thousand salinity and tolerated up to 363 per thousand salinity, but it failed to grow below 75 per thousand salinity, indicating that it could be a borderline extreme halophile. On the basis of its morphological features and position in 18S rRNA trees we propose a novel genus for our isolate; Halocafeteria, n. gen. The species name Halocafeteria seosinensis sp. nov. is proposed.

Microbial diversity of hypersaline environments: a metagenomic approach

“…Ideally, categorization should be based on the environmental conditions at which they naturally live instead laboratory ones. Cellular life in hypersaline habitats is dominated by prokaryotes (archaea and bacteria), with a few microbial eukaryotes, such as photosynthetic and heterotrophic protists and fungi, and the crustacean Artemia salina [1,[5][6][7][8]. Also, viruses are a significant part of the community [9,10].…”

Adaptations to High Salt in a Halophilic Protist: Differential Expression and Gene Acquisitions through Duplications and Gene Transfers

“…True halophilic microbes require the presence of salt to grow optimally and several cannot divide at salt concentrations under ~9%, which is around three times the salinity of seawater (Gochnauer et al, 1975; Oren, 2002a; Park et al, 2006, 2007, 2009; Cho et al, 2008; Kunčič et al, 2010; Park and Simpson, 2011; Foissner et al, 2014). Challenges faced by these organisms include ionic stress (especially the toxicity of sodium and chloride ions), osmotic stress, dehydration/desiccation stress (induced by complete evaporation), and reduced solubility of metabolites including nutrients and oxygen.…”

“…The bicosoecid stramenopile Halocafeteria seosinensis was first isolated from a 30% salt Korean saltern (Park et al, 2006), and the Halocafeteria clade has been frequently observed in hypersaline water samples from various geographic locations (Park and Simpson, 2015). H. seosinensis strain EHF34 grows optimally at 15% salt and still divides at 30% salt, but cannot grow at salinities <7.5% (Park et al, 2006).…”

“…H. seosinensis strain EHF34 grows optimally at 15% salt and still divides at 30% salt, but cannot grow at salinities <7.5% (Park et al, 2006). Analysis of its inferred cytoplasmic proteome revealed a molecular signature suggestive of a higher intracellular salt content than in marine protists (Harding et al, 2016).…”

Most ciliated protozoa in extreme environments are cryptic in the ‘seed bank’

“…Hypersaline habitats are considered extreme ecosystems (Madigan & Marrs 1997, Horikoshi & Grant 1998, Rothschild & Mancinelli 2001, Mancinelli & Rothschild 2002. Biological diversity in these extreme environments is reduced; however, major groups of prokaryotes (Cho 2005, Hauer & Rogerson 2005, microbial eukaryotes (Esteban & Finlay 2003, Park et al 2006) and even some metazoa (Elloumi et al 2009) tolerate extreme salinity conditions. The cosmopolitan ciliate Fabrea salina, rotifers, copepods, ostracods and the anostracod Artemia salina are amongst the best known examples.…”