ZOOFLAGELLATES: CHARACTERISTICS, CLASSIFICATION AND DISEASES - BIOLOGY - 2024

The zooflagelados or zoomastigóforos are polifilético group of unicellular organisms characterized by lack chromoplasts. Most have one to many flagella, however, some may lack these, generally they have amoeboid forms.

They are predominantly parasites. Its classification is based mainly on the presence and number of flagella, as well as other structures such as the loriga and the cytocollar.

Sphaeroeca, a colony of Choanoflagellates. Photograph by: Dhzanette. Taken and edited from:

In traditional taxonomy, zooflagellates constituted a class within the phylum Protozoa. This group contained extremely diverse species that shared in common only the absence of chromoplasts and other characteristic structures of phytoflagellates.

It was subdivided into at least seven orders. The group of zooflagellates currently lack taxonomic validity due to their polyphyletic condition.

characteristics

The scourge

A flagellum is a long, whip-shaped, mobile appendage of the same thickness throughout and with a rounded apex. Its central part is made up of a structure called the axoneme.

The axoneme is made up of a series of protein microtubules arranged in pairs, a central pair surrounded by nine concentric pairs.

At the base of the flagellum is a centriole-like structure called the basal body, blepharoplast, or kinetosome.

The flagellum flails or moves in a helical fashion, which allows the body to propel the body forward. This movement is achieved thanks to contractions and dilations of the proteins that make up the microtubules.

Loriga or lorica

The loriga is a protective surface structure secreted by many species of protozoa. The chemical composition of loriga is highly variable, it can be protein, siliceous, calcareous, or mucopolysaccharides.

It can also include various materials such as grains of sand, coccolithophores, among others, cemented according to a regular pattern. The shape can be capsule, bell, glass, arborescent, among others.

The necklace or cytocollar

The collar is a crown-shaped structure that surrounds the base of the flagellum. This structure is made up of fingerlike cell extensions called microvilli, which are covered with mucus. Its function is to increase the cell exchange surface of zooflagellates.

Classification

In traditional taxonomy, the class zoomastigophores or zooflagellates is made up of the following groups:

Choanoflagellates

Group of aquatic zooflagellates. They are characterized by presenting a single flagellum and a loriga with the shape of an open cage at the end where the flagellum and the collar are located.

They can be swimmers or live fixed to the substrate by means of a peduncle. In sessile choanoflagellates, the peduncle is opposite where the flagellum arises.

Currently this group is still considered valid, although it is considered a class (Choanoflagellatea) within the phylum Choanozoa, Protista or Protozoa kingdom. It is made up of about 150 species divided into 50 genera.

Rhizomastiginos

In classical taxonomy, Rhizomastigines are zooflagellates with pseudopods and present from one to four flagella (sometimes without flagella), which occur simultaneously or at different stages of their life cycle.

The group has predominantly free-living species. The organisms of this taxa are currently restricted to a single genus, Rhizomastix.

All the species included in this genus are monoflagellates, without mitochondria, and endosymbionts of insects and amphibians. Another characteristic of these species is the transformation of the collar into a structure called rhizostyle. They constitute an order within the phylum Amebozoa (Protista).

Kinetoplastids

They present two to four flagella. The kinetoplast (a granule that contains mitochondrial DNA and is associated with the base of flagella) is self-replicating. They are stained with silver and Feulgen's reagent.

Currently they make up a class (Kinetoplastea) of the phylum Euglenozoa (Protista), and includes species found in the soil and in aquatic environments, also parasitic species of animals, including humans, and plants.

Retortomonadines

The Retortomonadinos are characterized by presenting two to four flagella. One of the flagella is folded towards the posterior end and is associated with a cytostome (kind of cellular mouth) located ventrally.

In the current classification the group is restricted to two genera, Retortamonas with two flagella and Chilomastix with four. The species are considered mainly commensal although they can be free-living. They constitute a class (Retortamonadida) within the phylum Metamonada (Protista).

Diplomonadians

They present bilateral symmetry, with duplicated cellular components and four flagella on each side of the cell, arranged symmetrically with respect to the main axis of the body. They are generally parasites.

The group is currently located in the class Diplomonadida, phylum Metamonasda, kingdom Protista.

Trichomonadines

With two to six flagella, one of which bends towards the posterior end. They are parasites and symbionts of insects that feed on wood.

The current taxonomic location of the Trichomonadics is: class Trichomonadida, phylum Metamonasda, kingdom Protista. Currently it also includes parasitic species of vertebrates.

Diseases

Zooflagellates can cause different diseases in plants and animals, including humans. Among the diseases that can cause the latter are:

Trichomoniasis

Sexually transmitted disease caused by the zooflagellate Trichomonas vaginalis (Trichomonadins). The disease may be asymptomatic or present with symptoms including unusually heavy, light green or gray, nauseating and bubbly vaginal discharge, itching, burning, or redness of the vulva and vagina.

In men, it causes discharge from the penis, burning when urinating, conditions of the prostate and urethra. For both sexes, irritation of the bladder may occur. The infection, in men, can last about two weeks, in women, the parasite persists if there is no treatment consisting of Metronidazole.

Trichomonas vaginalis infestation. Photograph by: Alex_brollo. Taken and edited from:

Giardiasis

Giardiasis is a diarrheal disease caused by the zooflagellate Giardia intestinalis (Diplomonadino). The disease is transmitted by ingestion or contact with contaminated water, contaminated food, contact with sick people or their eating utensils, as well as unprotected anal sex.

The disease can be asymptomatic or present as diarrhea with pasty or liquid stools, nauseating, with mucus, colic and general malaise.

There may also be abdominal pain, nausea, and loss of appetite, among other symptoms. Treatment includes Secnidazole, Metronidazole, Tinidazole, Furazolidone, Albendazole, or Nitazoxanide.

Diseases caused by kinetoplastids

Kinetoplastids of the order Trypanosomatida are generally very aggressive parasites. They present complex life cycles in which more than one host is involved.

These species have several stages in their life cycle, each with different body shapes. They are responsible for different diseases that affect humans.

These include African trypanosomiasis or sleeping sickness, transmitted by the tsetse fly, Chagas disease, transmitted by triatomine insects and both caused by species of the genus Trypanosoma.

Another disease is leishmaniasis, caused by Leishmania species and transmitted by sand flies.

References

1. PA Meglitsch (1972). Invertebrate zoology. H. Blume Editions. Madrid.
2. D. Moreira, P. López-García, K. Vickerman (2004). An updated view of kinetoplastid phylogeny using environmental sequences and a closer outgroup: proposal for a new classification of the class Kinetoplastea. International journal of systematic and evolutionary microbiology.
3. Protozoa. On Wikipedia. Recovered from: en.wikipedia.org.
4. RG Yaeger (1996). Protozoa: Structure, Classification, Growth, and Development. Recovered from: ncbi.nlm.nih.gov.
5. SM Adl, AGB Simpson, CE Lane, J. Lukes, D. Bass, SS Bowser, MW Brown, F. Burki, M. Dunthorn, V. Hampl, A. Heiss, M. Hoppenrath, E. Lara, LL Gall, DH Lynn, H. Mcmanus, EAD Mitchell, SE Mozley-Stanridge, LW Parfrey, J. Pawlowski, S. Rueckert, L. Shadwick, CL Schoch, A. Smirnov, FW Spiege (2012). The revised classification of eukaryotes. Journal of Eukaryotic Microbiology.
6. T. Cavalier-Smith (2010). Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree. Biology Letters.