Ciliates
Overview
Ciliates are part of a group called Protozoa, which means they are unicellular eukaryotic microorganisms. There are around 3,500 species that have been described by scientists with the potential of thousands more to still be discovered. Ciliate species can have a wide range in not only size, but complexity. These species can measure anywhere from 10 µm to as large as 4 mm long and include some of the most morphologically advanced protozoans.
Ciliates are easily recognized by their cilia or hair-like organelles which are structurally similar to flagella. These organelles can be found in most members of the group. Cilia are more numerous and generally shorter than flagella. and are variously used in swimming, eating, staying in place, and other general movement.
Ciliates are protists and love water. These organisms can be found almost anywhere there is water. Besides soil, Ciliates can be found in lakes, ponds, rivers, and even oceans.
History
The oldest ciliate fossils known are from the Ordovician Period. A separate description of fossil ciliates was published in 2007, of which came from the Doushantuo Formation in the Ediacaran Period. Ciliate fossils are extremely rare. Only a very few have been found preserved in amber or extremely fast phosphatization under unusual marine conditions.
Examples of Ciliates:
Paramecium : First ciliate to be used extensively for genetic studies, because conjugation could be controlled. Normally feeds on bacteria.
Tetrahymena : Used in genetics because of methods for controlling conjugation so that it occurs synchronously in a large populations. Relatively easy to isolate the two kinds of nuclei.
Stentor : Large ciliate used for grafting and micromanipulations. Its morphology of its outer layer is revealed by bands of blue pigment.
Cell Structure
Nuclei
Ciliates have a set of two different of nuclei, which is different from most protists. The first is called the diploid micronucleus, which is the smaller of the two. This nucleus carries the germline of the cell and is used to pass genetic material to offspring, meaning it is specialized for sexual exchange. As such, this nucleus does not contain nucleoli, meaning the micronucleus does not share its genes. The second, larger, nucleus is called the polyploid macronucleus, which takes care of general cell regulation. The macronucleus is formed by the micronucleus and displays the phenotype of the organism. The macronucleus is what allows vegetative growth because it is specialized with nucleoli to move RNA into ribosomes.
Conjunction
This is the process Ciliates must go through when the macronucleus needs to be regenerated due to cell age. The process involves two cells lining up and the micronuclei undergoing meiosis then fuse to form new micronuclei and macronuclei. Conjunction results in genetic recombination and nuclear reorganization within the cell. In most cases, the two partners are similar in size and shape. In uncommon situations, the conjoining cells may become permanently fused. This results in the conjugant cell being absorbed by the other cell.
Cell Body
Ciliates also contain several vacuoles that enclose food and waste. Digestive vacuoles form in the gullet as food particles are ingested, and then are circulated through the cell. Any remaining waste in these vacuoles is discharged through a point in the cell membrane called the cytoproct. Ciliates also have contractile vacuoles, which collect water and expel it from the cell to maintain osmotic pressure.
Reproduction
Ciliates reproduce asexually. This process involves various cases of fission, including binary. During fission, the micronucleus undergoes mitosis and the macronucleus undergoes amitosis. Afterwards, the cell divides in two, each with a copy of the micronucleus and the macronucleus.
The other types of fission that can occur in ciliate groups include:
Budding: the emergence of small offspring from the body of a mature parent
Strobilation: multiple divisions along the cell body, producing chain of new organisms
Palintomy: multiple fissions, usually within a cyst
Feeding
Ciliates are mostly heterotrophic, meaning they feed on smaller organisms. Food such as bacteria and algae, are swept into the”mouth” by the organism’s cilia. The food is moved by the cilia through the mouth pore into the gullet, which forms food vacuoles. Feeding techniques vary from species to species. Some ciliates are mouthless and feed by osmotrophy, while others are predatory and feed on other protozoa. There are also ciliates that parasitize animals.
References
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[2] Berthold, A., and M. Palzenberger. “Biology and Fertility of Soils.” Biology and Fertility of Soils, 4th ed., vol. 19, Springer-Verlag, 1995, pp. 348–356. SpringerLink.
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[6] Ekelund, Flemming, and Reginn Ronn. “Notes on Protozoa in Agricultural Soil with Emphasis on Heterotrophic Flagellates and Naked Amoebae and Their Ecology.” FEMS Microbiology Reviews, vol. 15, no. 4, Dec. 1994, pp. 321–353. Wiley Online Library.
[7] Foissner, Wilhelm & Berger, Helmut. (1996). A user-friendly guide to the ciliates (Protozoa, Ciliophora) commonly used by hydrobiologists as bioindicators in rivers, lakes, and waste waters, with notes on their ecology. Freshwater Biology. 35.
[8] Foissner, Wilhelm & O'Donoghue, PJ. (1989). Morphology and infraciliature of some freshwater ciliates (Protozoa : Ciliophora) from Western and South Australia. Invertebrate Systematics - INVERTEBR SYST. 3. 10.
[9] Li, C.-W.; et al. (2007). "Ciliated protozoans from the Precambrian Doushantuo Formation, Wengan, South China". Geological Society, London, Special Publications. 286: 151–156.
[10] Mackean, D G. “Biological Drawings: Protista. Paramecium.” Biology Teaching and Learning Resources, www.biology-resources.com/drawing-paramecium-reproduction.html.
[11] Spiller, Marco. “Paramecium Reproduction.” BiologyWise, BiologyWise, biologywise.com/paramecium-reproduction.
[12] Slabodnick, Mark M., and Wallace F. Marshall. “Stentor Coeruleus.” Advances in Pediatrics., U.S. National Library of Medicine, 8 Sept. 2014, www.ncbi.nlm.nih.gov/pmc/articles/PMC5036449/.
[13] Waggoner, Ben. “Ciliata: Morphology.” More on Morphology of the Ciliata, University of California Museum of Paleontology, 2 Dec. 1995.