Synula, a colony of brown flagellates is travelling from particle to particle. The colony is composed of about ten or more individual flagellates with long flagella. One member seems to be dividing.
Commentary by Prof. Yuji Tsukii, Hosei University The commentary in the video “One member seems to be dividing” may not be correct. Although it may look like a flagellate in this Synula colony is dividing, it may in fact be two chloroplasts facing each other. Each cell member of Synula and Mallomonas has two chloroplasts by nature. It is likely that one cell in the colony has died, leaving two exposed chloroplasts.
However, we can’t rule out the possibility that this Synula colony is in the course of cell division. This is because careful observation reveals that the tip of cytoplasm surrounding the chloroplasts has become dented, suggesting that division might initiate.
In this video, it is very difficult to tell exactly what is occurring: is it cell division; are contents of a dead cell being discharged; or is a damaged flagellate being ejected from the colony after colliding with something? When Synula’s colony is disintegrated into single cells, these cells cannot be distinguished from single Mallomonas cells that are not part of a colony.
This view shows the rolling locomotion of Synula between particles. The surface of each particle is covered with bacteria and algae. These biofilms offer a rich environment to protozoa and other small organisms.
Commentary by Prof. Yuji Tsukii, Hosei University A plate-like figure appearing right side of the video is
a colony of blue-green algae, Merismopedia.
Synula grows into a large colony and divides into smaller ones
Several Synula (colonies of brown flagellates) take turns feeding on a large particle. Successful feeding causes the Synula to grow larger, which makes it difficult to move quickly. One large Synula disappears briefly behind the particle and reappears as two smaller colonies, apparently having divided just out of view.
Commentary by Prof. Yuji Tsukii, Hosei University (a) This video shows how a colony of Synula divides from one large colony
to a smaller one, rather than each flagellate member dividing individually.
Synula is a colony of flagellate cells that, in the course of its symbiotic
development, has included algal chloroplasts inside its flagellate members.
Therefore Synula can get nutrients from the photosynthetic activity of those chloroplasts.
But it is also possible that each flagellate in a Synula colony has the ability to take in food from outside.
(b) There are non-colonized flagellates that can take in food from outside.
(c) Ochromonas is a single-celled, motile, golden- brown alga, with the ability to perform photosynthesis, phagocytosis and osmotrophy. Therefore Ochromonas is easily cultured without bacterial food.
This large particle is covered with a bacterial biofilm, which provides a rich feeding ground for various organisms. As a Synula colony feeds on the bacteria, its member flagellates grow and divide, causing the Synula to become longer before our eyes. Between this long Synula and the particle surface, other small flagellates are absorbed in eating.
Commentary by Prof. Yuji Tsukii, Hosei University Although the commentary of this video says “each member flagellate repeatedly divides,” no member flagellate of this Synula colony seems to be dividing in this video. In general, it takes from 30 minutes to a few hours for a flagellate cell to complete the dividing process. Therefore, it is almost impossible for us to observe cell division within the time limit of this video.
In addition, the first part of the commentary states that “a large particle provides a rich feeding ground for various organisms,” and the final part of the commentary says that “as a Synula colony feeds on bacteria, its member flagellates grow and divides.” However, there is no video evidence to support these descriptions.
In the video there are scenes of various small protozoa running into this large particle, but these protozoa may not be feeding on bacteria, because most small protozoa sustain themselves through photosynthetic activity or by absorption of dissolved nutrients around them (osmotrophy).
Large and small colony of Synula are moving around an aggregate. However, becoming too large may be inconvenient, so here we can see the division of one big colony into two smaller ones.
Commentary by Prof. Yuji Tsukii, Hosei University The title of this video, “dividing Synura” is incorrect. This video shows how a single colony of Synura divides into two individual colonies, but does not show the division of cells. Also the comment that Synura is eating bacteria may not be true.
As this organism is a type of algae, it obtains nutrients through photosynthesis by its internal chloroplasts. But considering that Synura and related organisms have evolved with symbiotic algae inside their cells, the organism might have maintained the ability to forage bacteria.
In fact, some species of Dinoflagellate eat bacteria, and Ochromonas which have internal chloroplasts also eat bacteria. Ochromonas are able to get nutrients not only through photosynthesis and phagocytosis but also through osmotrophy. Therefore this organism is easily cultured without adding bacteria.
Various sizes of Synura(flagellate colonies) visit the big particle to forage for food. To share the food equally, the colony needs to rotate periodically so that each individual member can access the particle surface. Meanwhile, the number of cells in one of the colonies increases and the whole colony becomes larger, probably because the individual members have multiplied. However, becoming too large may be inconvenient, so here we can see the division of one big colony into two smaller ones.
Commentary by Prof. Yuji Tsukii, Hosei University As Synura belongs to Chrysophyceae, its growth depends on photosynthesis.
Actually I have never observed Synura eating bacteria. Furthermore, in this video we cannot see a structure like a food vacuole in each cell of the Synura colony, nor can we observe the process of cell division or colony separation.
Therefore the title of this video referring to repeated division is not accurate.
A colony of brown flagellates, Synura, rolls slowly along the surface of particles or quickly rotates in open water. When it reaches the outer boundary of water and encounters air, it must stop. Here, some contents of the colony are gradually discharged. The flagella of each flagellate stop waving as the whole colony shrinks and finally collapses with the flagellates floating apart.
Commentary by Prof. Yuji Tsukii, Hosei University To identify the Synura species, an electron microscope is necessary
to observe the cell's scale-like surface pattern.
Therefore, it is difficult to determine the species using an optical microscope.