Cryptomonads

Abstract

Cryptomonads are a group of unicellular, biflagellate protists occurring in a variety of aquatic habitats. Several nonpigmented forms exist but the vast majority bear plastids containing chlorophylls a and c, and accessory pigments known as phycobiliproteins. Plastids of cryptomonads are derived from a secondary endosymbiotic event involving the engulfment of a unicellular red alga, its retention as an endosymbiont, and its conversion into a photosynthetic organelle. Unique features of cryptomonads include the cell covering termed a periplast, the surface architecture consisting of a furrow and/or gullet, extrusive organelles called ejectisomes, and the presence of a reduced eukaryotic genome known as the nucleomorph. Accurate identification of cryptomonad species using light microscopy is problematic owing to the range of morphological plasticity and the presence of two distinct morphotypes in certain species. In addition to traditional morphological characters, proper diagnosis of species cannot exclude molecular data.

Key Concepts:

  • Accurate identification and estimation of cryptomonads from field samples requires counting cells in the living state.

  • Proper characterisation of cryptomonad periplast plates requires use of quick‐freezing and freeze‐fracture techniques.

  • Accumulating karyotypic data continues to provide insight into the genetic variability of nucleomorph genomes, which may prove systematically significant.

  • Cryptomonad biliproteins all derive from an ancestral phycoerythrin, which has since evolved into at least seven spectral types.

  • Morphological species concepts are problematic given the increasing awareness of morphological plasticity and dimorphisms among cryptomonads.

  • Resolution of the large‐scale phylogentic affinities of cryptomonads remains tenuous and additional molecular analyses are required.

Keywords: algae; algal systematics; cryptomonad phylogeny; cryptomonads; Cryptophyceae; nucleomorph; phycobiliproteins; protists; secondary endosymbiosis

Figure 1.

Illustration of a typical cell of Goniomonas including ultrastructural detail. Members of this genus are primitively colourless and lack a periplastidial complex. DB, digested bacterium; F, furrow; FV, food vacuole; I, infundibulum; LE, large ejectisome; LF, long flagellum; M, mitochondrion; N, nucleus; RP, rectangular plate; S, stoma; SF, short flagellum; and V, vestibulum.

Figure 2.

Illustration of a typical cell of Pyrenomonas including ultrastructural details. Note the pyrenoid embedded in the nucleomorph. C, chloroplast; F, furrow; G, gullet; ISP, inner square plate; LE, large ejectisome; LF, long flagellum; M, mitochondrion; N, nucleus; Nm, nucleomorph; P, pyrenoid; SE, small ejectisome; SF, short flagellum; and V, vestibulum.

Figure 3.

Illustration of typical cells of the Cryptomonas cryptomorph and campylomorph including ultrastructural details. CF, complex furrow; EP, ejectisome pore; F, furrow; FP, fibrous furrow plate; G, gullet; IPS, inner periplast sheet; IOP, inner oval plate; LE, large ejectisome; LF, long flagellum; M, mitochondrion; N, nucleus; Nm, nucleomorph; P, pyrenoid; S, stoma; SE, small ejectisome; SF, short flagellum; SG, starch grain; SP, scalariform plate; V, vestibulum; and VL, vestibular ligule.

Figure 4.

Illustration of a typical cell of Chroomonas including ultrastructural detail. Note the eyespot which is present in some species of Chroomonas. C, chloroplast; E, eyespot; G, gullet; IRP, inner rectangular plate; LE, large ejectisome; LF, long flagellum; M, mitochondrion; N, nucleus; Nm, nucleomorph; P w/T, pyrenoid with traversing thylakoids; SE, small ejectisome; SF, short flagellum; SG, starch grain; and V, vestibulum.

Figure 5.

Formation of the cryptomonad chloroplast endoplasmic reticulum (CER) and periplastidial complex by secondary endosymbiosis. The resultant cryptomonad is a composite organism that possesses four genomes. RER, rough endoplasmic reticulum.

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References

Archibald JM (2007) Nucleomorph genomes: structure, function, origin and evolution. BioEssays 29: 377–385.

Cavalier‐Smith A and Chao EE (2006) Phylogeny and megasystematics of phagotrophic heterokonts (Kingdom Chromista). Journal of Molecular Evolution 62: 388–420.

Cavalier‐Smith T, Couch JA, Thorsteinsen KE et al. (1996) Cryptomonad nuclear and nucleomorph 18S rRNA phylogeny. European Journal of Phycology 31: 315–328.

Clay BL and Kugrens P (1999) Characterization of Hemiselmis amylosa sp. nov. and the phylogenetic placement of the blue/green cryptomonads H. amylosa and Falcomonas daucoides. Protist 150: 297–310.

Deane JA, Strachan IM, Saunders GW, Hill DRA and McFadden GI (2002) Cryptomonad evolution: nuclear 18S rDNA phylogeny versus cell morphology and pigmentation. Journal of Phycology 38: 1236–1244.

Douglas SE, Murphy CA, Spencer DF and Gray MW (1991) Cryptomonad algae are evolutionary chimeras of two phylogenetically distinct unicellular eukaryotes. Nature 350: 148–151.

Douglas SE and Penny SL (1999) The plastid genome of the cryptophyte alga, Guillardia theta: complete sequence and conserved synteny groups confirm its common ancestry with red algae. Journal of Molecular Evolution 48: 236–244.

Fast NM, Kissinger JC, Roos DS and Keeling PJ (2001) Nuclear‐encoded, plastid‐targeted genes suggest a single common origin for apicomplexan and dinoflagellate plastids. Molecular Biology and Evolution 18: 418–426.

Gillot MA and Gibbs SP (1980) The cryptomonad nucleomorph: its ultrastructure and evolutionary significance. Journal of Phycology 16: 558–568.

Glazer AN and Appell GS (1977) A common evolutionary origin for the biliproteins of cyanobacteria, Rhodophyta, and Cryptophyta. Federal European Microbiological Society, Microbiological Letters 1: 113–116.

Hill DRA and Wetherbee R (1986) Proteomonas sulcata gen. et sp. nov. (Cryptophyceae), a cryptomonad with two morphologically distinct and alternating forms. Phycologia 25: 521–543.

Hoef‐Emden K (2008) Molecular phylogeny of phycocyanin‐containing cryptophytes: evolution of biliproteins and geographical distribution. Journal of Phycology 44: 985–993.

Hoef‐Emden K and Melkonian M (2003) Revision of the genus Cryptomonas (Cryptophyceae): a combination of molecular phylogeny and morphology provides insights into a long‐hidden dimorphism. Protist 154: 371–409.

Keeling PJ (2009) Chromalveolates and the evolution of plastids by secondary endosymbiosis. Journal of Eukaryotic Microbiology 56: 1–8.

Kugrens P, Clay BL and Lee RE (1999) Ultrastructure and systematics of two new freshwater red cryptomonads, Storeatula rhinosa, sp. nov. and Pyrenomonas ovalis, sp, nov. Journal of Phycology 35: 1079–1089.

Kugrens P and Lee RE (1987) An ultrastructural survey of cryptomonad periplasts using quick‐freezing freeze‐fracture techniques. Journal of Phycology 23: 365–376.

Kugrens P, Lee RE and Andersen RE (1986) Cell form and surface patterns in Chroomonas and Cryptomonas cells (Cryptophyta) as revealed by scanning electron microscopy. Journal of Phycology 22: 512–522.

Kugrens P, Lee RE and Andersen RE (1987) Ultrastructural variations in cryptomonad flagella. Journal of Phycology 23: 511–518.

Kugrens P, Lee RE and Corliss JO (1994) Ultrastructure, function and biogenesis of extrusive organelles in selected non‐ciliate protists. Protoplasma 181: 164–190.

Lane CE and Archibald JM (2008) New marine members of the genus Hemiselmis (Cryptomonadales, Cryptopheceae). Journal of Phycology 44: 439–450.

Lane CE, Khan H, MacKinnon M et al. (2006) Insight into the diversity and evolution of the cryptomonad nucleomorph genome. Molecular Biology and Evolution 23: 856–865.

Marin B, Klingberg M and Melkonian M (1999) Phylogenetic relationships among the Cryptophyta: analyses of nuclear‐encoded ssu rRNA sequences support the monophyly of extant plastid‐containing lineages. Protist 149: 265–276.

Martin W, Sommerville CC and Loiseaux‐de Goer S (1992) Molecular phylogenies of plastid origins and algal evolution. Journal of Molecular Evolution 35: 385–404.

McFadden GI (1993) Second‐hand chloroplasts: evolution of cryptomonad algae. Advances in Botanical Research 19: 189–230.

McFadden GI and Gilson PR (1995) Something borrowed, something green: lateral transfer of chloroplasts by secondary endosymbiosis. Trends in Ecology and Evolution 10: 12–17.

Okamoto N and Inouye I (2005) The katablepharids are a distant sister group of the Cryptophyta: a proposal for Katablepharidiophyta divisio nova/Kathablepharida phylum nova based on SSU rDNA and beta‐tubulin phylogeny. Protist 156: 163–179.

Wetherbee R, Hill DRA and McFadden GI (1986) Periplast structure of the cryptomonad flagellate Hemiselmis brunnescens. Protoplasma 131: 11–22.

Further Reading

Cavalier‐Smith T (1986) The Kingdom Chromista: origin and systematics. In: Round FE and Chapman DJ (eds) Progress in Phycological Research, vol. 4, pp. 309–347. Bristol: Biopress.

Gillot M (1990) Phylum Cryptophyta (Cryptomonads). In: Margulis L, Corliss JO, Melkonian M and Chapman DJ (eds) Handbook of Protoctista, pp. 139–151. Boston, MA: Jones & Bartlett.

Hill DRA (1991a) Diversity of heterotrophic cryptomonads. In: Patterson DJ and Larsen J (eds) The Biology of Free‐Living Heterotrophic Flagellates. Systematics Association Special Volume 45, pp. 235–240. Oxford: Clarendon Press.

Hill DRA (1991b) A revised circumscription of Cryptomonas (Cryptophyceae) based on examination of Australian strains. Phycologia 30: 170–188.

Kugrens P and Clay BL (2010) Cryptophyta. In: Algae: Source to Treatment, pp. 187–205. Denver, Colorado: American Water Works Association.

Kugrens P and Clay BL (2003) Cryptomonads. In: Wehr JD and Sheath RG (eds) Freshwater Algae of North America, pp. 715–756. Amsterdam, Boston: Academic Press.

Kugrens P and Lee RE (1991) Organization of cryptomonads. In: Patterson DJ and Larsen J (eds) The Biology of Free‐Living Heterotrophic Flagellates. Systematics Association Special Volume 45, pp. 219–233. Oxford: Clarendon Press.

Kugrens P, Lee RE and Hill DRA (2000) Order Cryptomonadida Senn, 1900. In: Lee JJ, Leedale GF and Bradbury P (eds) An Illustrated Guide to the Protozoa, pp. 1111–1125. Lawrence, Kansas: Society of Protozoologists.

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How to Cite close
Clay, Brec L(May 2011) Cryptomonads. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001976.pub2]