Chromalveolates

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  • Chromalveolata
    • Cryptomonads (Extrusome-containing alae)
    • Haptophytes (Coccolithophore algae & relatives)
    • Stramenopiles (heterokonts)
      • Diatoms
      • Raphidiphytes (Chloromonads)
      • Eustigmatophytes
      • Chrysophytes (golden algae)
      • Phaeophytes (Brown algae and brown seweeds, kelps))
      • Bolidophytes
      • Blastocycstis (non-phototrophic parasite commonly mistaken for yeast)
      • Actinophryids (freshwater heliozoans)
      • Labyrinthulids (slime nets)
      • Thraustochytrids (also slime nets)
      • Oomycetes (water molds, animal parasites often mistaken for fungi)
      • Opalinids (obscure animal commensals)
      • Bicosoecids
    • Alveolata
      • Apicomplexa (Plasmodium, Cryptosporidium, Toxoplasma, & relatives)
      • Colpodella
      • Dinoflagellates
      • Oxyhrris
      • Perkinsus (Dermo oyster disease agent)
      • Ciliates
      • Colponema
      • Eliobiopsids

About this Superkingdom

Chromalveolates are eukaryotic algae that probably originated by endosymbiosis of a flagellate (a bikont) with red alga (rhodophyte), although it may also be that different groups within the chromalveolates acquired plastids independently. Regardless, many groups of chromalveolates have lost their plastids and the ability to grow phototrophically. Their mitochondria have tubular cristae.

The stramenopiles (also known as the heterokonts) are an abundant and diverse group of eukaryotes. Most are phototrophic, and those that have lost the ability to grow phototrophically are parasitic.

Stremenopiles

Most heterokonts are biflagellated at some stage of their life cycles, usually at least as gametes. The two flagella are structurally distinct, the leading-end flagella (“tinsel”) being branched, the lateral or subapical flagellum is smooth and shorter or even rudimentary. Their plastid envelops consist of 4 membrane layers. The innermost 2 layers are derived from the original cyanobacterial endosymbiont. The next layer is the relic of the cell membrane of the red alga from which the stramenopilie acquired the plastid by seconadry endosymbiosis. The outermost layer is actually the host endoplasmic reticulum, inside of which the plastids reside.

Diatoms are the most familiar members of this group, and are perhaps the most abundant and diverse as well. By some estimates, they may be responsible for up to half of marine primary production. Most are unicellular. Gametes are flagellated, but diploids are non-motile or motile by gliding, and are encased in a intricate 2-part silica (glass) shells. Common in freshwater as well as marine environments, they produce an exopolysaccharide matrix that, when purified, is used as a non-toxic adhesive (mucilage) for children and old-fashioned “lickable” postage stamps.

Phaeophytes (brown algae) are common multicellular marine algae. Most are macroscopic; the giant kelp can reach lengths of over 105ft and form submarine forests. Brown rockweeds are common in the intertidal zone, and sargassum is an abundant free-floated group of species. These “plants” are composed of a root-like holdfast, a stipe (stalk), which may or may not be divided, and fronds (lamina). Gas-filled vesicles in the stipes or fronds are used in many species for buoyancy.

Crysophytes (golden algae) are generally freshwater unicellular flagellates, with one or two flagella. Some have an amoeboid phase in their life cycle with hairlike pseudopods. Many form a vase-like chitinous shell (lorica), and some of these are colonial. Resting stages have complex silica shells.

Actinophryids are common freshwater heliozoans, amoeboids with many straight, rigid pseudopods supported by internal microtubule structures.

Labyrinthulids and Thraustochytrids are primarily marine slime nets. They are unicellular heterotrophs (lacking plastids) that produce a network of polysaccharide filaments, along which they glide. Interestingly, although these filaments are external to the cells, they are nevertheless surrounded by a cytoplasmic membrane.They are common symbionts or parasites residing on the surface of marine seagrass.

Oomycetes are heterotrophic (non-phototrophic) and filamentous, and were long thought to be fungi. Most are plant or fish pathogens, but some are water “molds”. They cause a variety of wilts and rusts in plants. The best-known are the Phytophthora, which cause chestnut ink disease, sudden oak death, and potato blight.

Other stramenopiles are relatively obscure phototrophs or parasites.

Example species :

Navicula sp.

Navicula
from Texas Tech University at Junction - llano River Field Station

Navicula is a large genus of common diatoms. with something like 10,000 phenotypically-distinguishable types. Like many diatoms, it has a long slit (raph) down the long axis of each valve, from with muscilage is secreted for gliding motility. Navicula are bilaterally symmetrical (pennate). Each half of the silica shell has the general shape of a small boat, from which the genus gets its name. The cell contains two large brown-pigmented plastids that lie side-by-side down the length of the cell.

Phytophthora infestans

Phytophthora_infestans
from Kay Yeoman, U of East Anglia

Phytophthora is a pathogenic oomycete that causes a range of serious diseases in plants. P. infestans infects plants of the family Solanaceae (nightshades), including potatoes. P. infestans was the cause of the infamous Irish Potato Blight of the mid 1800’s, in which over 1,000,000 people starved. Phytophthora resembles a fungus morphologically, and diseases caused by them resemble fungal wilts and rots, and so even today antifungals are often used, with only marginal effect, to treat Phytophthora blights.

Alveolates

Although the different groups of alveolates are quite distinct, they share a pellicle underlying their cell membrane, composed of many flattened membranous vesicles joined into a tough laminate. Most lack plastids.

Ciliates are the most familiar alveolates. Ciliates contain numerous short flagella (cilia) used in locomotion and feeding. Many are quite large, 1-2mm in length, and are anatomically very complex, rivaling in size and mirroring in structure small animals such as rotifers. Ciliates feed by sweeping Bacteria and other small organisms into their oral groove into a “gullet” where phagocytosis occurs. When digestion in food vacuoles is complete, the vacuoles fuse with the cytoproct (analogous to an anus) to eliminate the waste. Star-shaped contractile vacuoles in freshwater species collect excess water, which is forced out of the cell through pores upon vacuole contraction. Ciliates contain two types of nuclei; a germ-line micronucleus containing a pristine diploid copy of the genome, which is apparently transcriptionally inactive, and large active macronuclei. Fission is the most frequent form of reproduction, but cells must periodically undergo sexual reproduction involving meiosis of the micronucleus and exchange of one haploid micronucleus with a partner. The two haploid micronclei fuse in each cell, and new macronuclei are generated from these by mitosis (the old macronuclei are degraded).

Dinoflagellates are common marine flagellates (some are also found in freshwater), often with plastids, although sometimes these are acquired temporarily by partial digestion of food algae (“kleptochloroplasts”). Blooms of some species along the coast result in red tide. Dinoflagellates have complex life cycles. Alveoli support cellulose plates that cover the cell. Two flagella are present; the coiled posterior flagellum (longitudinal) and the lateral (transverse) flagellum.

Apicomplexa are intracellular parasites of animals with a specialized apical structure (probably a highly modified basal body) used to enter the host cell. They have complex life cycles, often with primary and secondary hosts, and both sexual and asexual reproduction. Although they are not phototrophic, most contain non-pigmented plastids (that are apparently secondary endosymbionts, like those of dinoflagellates) of unknown function. The most familiar (or at least infamous) apicomplexian is Plasmodium, the causative agent of malaria, probably the most important infectious disease of humans.

The other alveolates (Colpodella, Oxyhrris, Perkinsus, Colponema, and Eliobiopsids) are small, unfamiliar groups.

Example species

Vorticella sp.

Vorticella
from wikicommons : http://en.wikipedia.org/wiki/File:Vorticella.JPG

Voricella are common freshwater peritrichous ciliates. These are bell-shaped, with a stalk (and holdfast) at one end that can contract quickly if disturbed, and a ring of cilia and membrane sheets circling the oral cavity. Asexual reproduction is fission; only one cell keeps the stalk, the other has a ring of cilia ate the posterior (stalk) end by which they can swim until attaching to a substrate and developing a stalk. In poor environments, stalked cells can develop posterior cilia, lose their stalk, and swim in search of better conditions.

Karenia (Gymnodium) breve

red tide
from P. Schmidt, Charlotte (FL) Sun.

K. breve is the dinoflagellate that causes Florida red tide. Although these blooms rarely become dense enough to turn the water red, K. breve produces a potent neurotixin (brevetoxin) that results in serious fish and shellfish kills. Although red tides are a natural phenomenon, they were historically rare and occurred only in the summer; nutrient-rich run-off from human development has resulted in red tides becomes much more frequent, severe, and now occur year-round. Breathing brevetoxin aerosolized in the surf causes “tourist’s cough”.