Cells of Cafileria marina were sampled from part of an algal mat community in a rock surface from Kvernesfjord, Norway. Their morphology, ultrastructure, flagellar apparatus and mitochondrialgenome were investigated. The results, along with the formal taxonomic description of Cafileria marina, were published in 2019 by Czech researchers Dagmar Jirsová, Zoltán Füssy, Jitka Richtová, Ansgar Gruber and Miroslav Oborník.[1]
Cafileria is named after kafilerie [cs], the Czech name for a rendering plant where the biomass of animal origin is transformed for the production of lipids, glue and fertilizers. In a parallel manner, Cafileria feasts on bacteria and recycles organic materials that are part of their biofilm habitat. The species epithetmarina is due to the marine origin of the species.[1]
Cell structure
External appearance
Cells of C. marina are rounded on the right side and flattened on the left side, resembling the shape of a "D". The cell body is 3–4 μm wide and 5–6 μm long, making it a nanoflagellate by size. The cellular surface is smooth, without any features (no lorica, cell wall, etc.) visible by light or scanning electron microscopy. Like other bicosoecids, they have two smooth flagella (anterior and posterior), with an equal length of around 1.5–2 times the length of the cell body. The flagella are in a sub-apical position and emerge from a dent on the ventral side.[1]
Organelles
Connections between the nucleus (nc) and the mitochondria (mt) seen in Cafileria marina through TEM
C. marina cells localize their nucleus and mitochondria with tubular cristae (as is common in Stramenopiles) in the anterior part of the cell. A peculiar phenomenon in C. marina is that, in young cultures (≤ 2 weeks old), the nucleus and mitochondria are tightly connected through junctions. Although clustering of mitochondria near the nucleus is seen in mammaliantissues,[2][3] this is the first time that a full connection between these compartments has been described. Various functions for this peculiar connection have been hypothesized:
(i) enabling the exchange of ATP/ADP between the two organelles, thereby providing the high energy needed by the nucleus,
(ii) facilitating the transport of necessary nuclear tRNA that the mitochondria cannot produce,
(iii) transporting mRNA to be translated in the mitochondria,
(iv) equally segregating mitochondria to the daughter cells after mitosis,
(v) or simply a more efficient use of the limited space in a small cell size.[1]
The Golgi apparatus is in the anterior part of the cell, with its 4–5 cisternae aligned parallel to the nuclear envelope. During the cell cycle, the shape of the Golgi cisternae changes from flat-stacked to rounded: the flat cisternae curve inside and create hollowed rounded shapes. A similar phenomenon happens in mammalian cells, in association with changes in sphingomyelin metabolism,[4] but in the case of Cafileria the mechanism responsible is unknown.[1]
Several small vesicles are scattered across the cytosol, while food vacuoles are considerably larger and are localized in the posterior part of the cell, occupying almost one third of its volume. Some of the food vacuoles can contain intact or partially digested bacteria.[1]
3D reconstruction of the flagellar apparatus of Cafileria marina. AB: anterior basal body; BC: connection between basal bodies; PB: posterior basal body; R1–4: microtubular roots; x: additional microtubular structure; A: anterior; P: posterior; L: left; R: right.
C. marina has its two flagella attached to four roots made of microtubules. There are two basal bodies, in the anterior (front) part of the cell, at a 45° angle to each other, connected to each other through a striated fiber. The flagella each have an axoneme structure with two central microtubules and a circle of nine microtubules around them. The four roots (named R1, R2, R3 and R4) have 8, 3, 1, and 1 microtubules respectively, an arrangement unique to C. marina.[1]
Ecology and cell behavior
Cafileria marina lives in close association with an unidentified species of pelagophyte alga. It glides through the mucilage secreted by the pelagophyte. While moving, it exhibits a tumbling motion, with the anterior flagellum freely sweeping while the posterior one is used as an anchor, attached to the surface. It is constantly feeding through phagotrophy, with a permanent cytostome; no resting stages or spores have been observed.[1]
Cafileria belongs to the Bicosoecida lineage, a basal stramenopile clade, but its position within this group is still unclear. According to the study that described Cafileria marina in 2019, phylogenetic and morphological analyses group the family Cafeteriidae as the closest relative of Cafileria marina, with Caecitellus as the sister taxon of C. marina, though the authors explain "further investigation is [...] needed to confirm this claim".[1] A posterior analysis from 2022 recovered Cafileria outside the Anoecales; as the authors put it, "The phylogenetic resolution of the bicosoecids is still an ongoing issue".[5]
^ abSchoenle A, Hohlfeld M, Rybarski A, Sachs M, Freches E, Wiechmann K, Nitsche F, Arndt H (2022). "Cafeteria in extreme environments: Investigations on C. burkhardae and three new species from the Atacama Desert and the deep ocean". European Journal of Protistology. 85: 125905. doi:10.1016/j.ejop.2022.125905. PMID35868212. S2CID249935619.