Apicomplexa

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Apicomplexa
Toxoplasma gondii

Toxoplasma gondii

Systematics
Classification : Creature
Domain : Eukaryotes (eukaryota)
without rank: Diaphoreticks
without rank: Sar
without rank: Alveolata
without rank: Apicomplexa
Scientific name
Apicomplexa
Levine , 1970

The apicomplexa (from the Latin apex = point) are single-cell parasites belonging to the eukaryotes that produce infectious sporocysts or oocysts and go through a characteristic generation change in which sexual and asexually reproducing cells alternate.

Well-known representatives are the malaria pathogens of the genus Plasmodium and Toxoplasma gondii , the causative agent of toxoplasmosis .

features

Characteristic features of the apicomplexa are:

  • a pole ring complex at the apical end,
  • a conoid that apparently serves to penetrate the host cell membrane ,
  • Rhoptria containing lytic enzymes and serine / threonine kinases and e.g. B. Involved in the breakdown of red blood cells
  • Micronemes, elongated structures based on membrane thickenings,
  • a “gliding” locomotion that takes place without flagella or flagella , cilia or changes in cell shape.

The apicomplexa have a specialized plastid , the apicoplast. In contrast to the plastids of the higher plants and green algae , the organelle has two additional covering membranes, making a total of four covering membranes. It is believed that the plastid developed from a red alga that was ingested by another cell in the course of a secondary endosymbiosis . The two inner envelope membranes come from the original plastids of the red alga, and one membrane each emerged from the cell membranes of the red alga and the host.

Proteins that are located in the apicoplast have their own two-part signal peptides that ensure transport across the cell membrane. The apicoplast has its own plastid genome , which is similar to that of plant plastids. Among other things, enzymes were found that are usually part of the photosynthesis apparatus in plants, but have different tasks in the apicoplasts, because the apicomplexa, as obligate endoparasites, do not photosynthesize . An example of this is ferredoxin-NADPH reductase, which is part of photosystem I in plants.

Multiplication

Most apicomplexes are haploid . Often the asexual phase of reproduction is a schizogony (syn. Merogony, decay division), in which a multinucleated stage (the schizont / meront ) divides into different numbers of cells (the merozoites ). Some merozoites can give rise to gamonts and later gametes , which fuse to form a zygote during gamogony (gametogamy) . After the meiosis and often a further asexual reproduction ( sporogony ), infectious sporozoites develop from the zygote , which can still be stuck in cyst envelopes .

Hosts

The Apicomplexa can have one or more hosts that can become infected in different ways. So z. For example, the oocysts are often excreted with the feces and can get into a new host through dirt and smear infection. Many sporozoa also develop permanent stages in a cyst shell in intermediate hosts , which can be ingested by a carnivorous ultimate host when consuming raw meat. In the case of the malaria pathogen, the sporozoites are transmitted by mosquitoes when they are bitten .

Systematics

Adl et al. (2012) divide the apicomplexa into the following groups:

proof

  1. ↑ Adl, SM, Simpson, AGB, Lane, CE, Lukeš, J., Bass, D., Bowser, SS, Brown, MW, Burki, F., Dunthorn, M., Hampl, V., Heiss, A. , Hoppenrath, M., Lara, E., le Gall, L., Lynn, DH, McManus, H., Mitchell, EAD, Mozley-Stanridge, SE, Parfrey, LW, Pawlowski, J., Rueckert, S., Shadwick, L., Schoch, CL, Smirnov, A. and Spiegel, FW (2012): The Revised Classification of Eukaryotes. Journal of Eukaryotic Microbiology , 59: 429-514, 2012, PDF Online .

Web links

Commons : Apicomplexa  - collection of images, videos and audio files