Mallomonas is a genus comprising unicellular algal eukaryotes and characterized by their intricate cell coverings made of silica scales and bristles. The group was first named and classified by Dr. Maximilian Perty in 1852. These organisms live in freshwater and are widely distributed around the world. Some well known species include Mallomonas caudata and Mallomonas splendens.
Mallomonas is a genus of many from the phylum Ochrophyta, which describes organisms as having heterokont flagella in some part of their life history. At first, the family Mallomonadaceae was placed under class Chrysophyceae. However, after finding key biochemical and ultrastructural differences, the family was then placed under the class Synurophyceae. In a broader context, both Chrysophyceae and Synurophyceae are referred to as “chrysophytes”, meaning “golden algae”, because of their close similarities. Despite being quite similar, there are various, noticeable differences.
History of knowledge
The genus Mallomonas was first named and classified by Dr. Maximilian Perty in 1852. It was assigned its own genus because Mallomonas consisted of individually living cells, while its sister group Synura is composed of colonial cells that are connected to one another through stalks.
Other distinguishing features that differentiate Mallomonas cells from Synura cells are the presence of bristles and V-shaped ridges on their scales. Pore-collar complexes on stomatocysts are species differentiating features.
Habitat and ecology
Mallomonas is composed of planktonic, freshwater organisms.
Cells range in many ecological factors. Many species can tolerate pH levels ranging from 4 to 8, and can live in slightly acidic waters. Some species prefer low phosphorus gradients. Temperature tolerance ranges from 1.5 to 25.5 °C.
According to the temperature-size rule, as the temperature increases, the size of protists decreases. As with all Synurophytes, the inorganic scales produced by organisms in the genus Mallomonas also decrease in size as a response to increasing temperature, the same way as the cells themselves decrease. The shape of the scales became less round and more elongated or oval-shaped. Also, higher temperatures negatively affect scale biogenesis, interfering with the cellular processes that produce the scales.
Description of organism
General characteristics
The organisms in this genus have streamlined morphology in spherical, oval, or elliptical forms, and they have a wide range of sizes that vary from the smallest being 10 µm to the largest being 100 µm. Two flagella emerge from the anterior apical flagellar pocket; one can be easily seen in the light microscope as it is longer and covered in hairs (called mastigonemes) while the other is much shorter, with no hairs, and is not as easily seen.
Pigments such as chlorophyll c1 and fucoxanthin within the chloroplasts cause the cells to have a distinct, golden or yellow-brown colour. The chloroplasts themselves are bi-lobed, but some cells have two single-lobed chloroplasts. Cells have a girdle lamella, grouped thylakoids stacked in three, and additional membranes around the chloroplast called the chloroplast endoplasmic reticulum (CER).
The large nucleus is located between the chloroplast and the Golgi complex. Vacuoles full of the storage product known as chrysolaminarin are found near the posterior end of the cell.
Flagella
Flagella are microtubule-based structures that allow cells to have controlled movement to a certain degree. The root of the microtubule arrangement that is associated with the flagellar basal bodies, R1, which is also the site of cytoskeletal microtubules, is positioned uniquely in the genus Mallomonas. Instead of pulling away from the basal bodies, R1 actually loops around them in a clockwise fashion. There is also a second root of microtubules extending from the point of origin towards the cell’s centre. Both basal bodies, each assigned one of the two flagella, are enclosed in a thick, fibrous capsule.
Morphometry
Scales
The genus Mallomonas is based on the organization of its scales, which are silica plates that are intricately designed, species-specific, and cover the cell. There are many parts to the entire structure; it’s made up of anterior spine scales, posterior spine scales, body scales, and some specialized scales. An example of a specialized scale is one that can fit around a flagellar pocket. The scales are accompanied by bristles, which are long, elongated structures that are tucked under the scales with the use of a small bend in the end, which is called a ‘foot’.