Several sizes of diatoms are living in Hirose River. This is one of the largest, and we can see two cells are surrounded by a membrane. Each cell is covered with a hard siliceous cell wall. The two cells may be in the process of division. Larger brown structures as well as small particles are moving inside the cytoplasm of the diatoms.
Commentary by Prof. Yuji Tsukii, Hosei University The yellowish-brown structure in one of these diatom cells may be a chloroplast losing its shape.
The organism seems not to be in the process of division, rather already dead. If the organism is alive and dividing, the brown structure (chloroplast) should be equally spread in both cells.
We cannot see one of them, and the remaining one is shrinking. These show that both cells are alreday dead.
Two different types of diatoms are stuck to each other and remain still in the middle of the screen. Other kinds of diatoms are moving around in the background.
Commentary by Prof. Yuji Tsukii, Hosei University Large diatoms are rather easy to identify by their shape, but medium-sized and small diatoms (which include a lot of species) are difficult to identify, even to the genus level. For identification at the species level, it is necessary to observe under high magnification the acid-treated cell wall pattern which is characteristic to each species.
A diatom caught by an unknown filamentous organism
A diatom and a long filamentous organism are stuck together in the middle of the screen. They cannot move freely, whereas other kinds of diatoms and a reddish-brown flagellate, Trachelomonas, are swimming actively.
Commentary by Prof. Yuji Tsukii, Hosei University The swimming organisms in the first half of this video are diatoms. A string-like organism , which may be a filamentous bacterium, is moving slightly at the center of the field. It may be Cyanobacteria though it is not green. To identify it clearly, observation with high magnification is necessary.
About 26 to 28 seconds after the video starts, an organism quickly travels from the lower-left to upper-right. At a first glance it looks like Trachelomonas, but the shape of its lorica( shell-like covering) is actually very different from that of Trachelomonas.
The lorica of this organism has a dent at the front of the cell, but Trachelomonas does not have this type of lorica. Organisms having a similarly dented lorica are found in green algae, such as Dysmorphococcus and Coccomonas. The organism in this video is most likely Coccomonas, although it cannot be verified because the poor focus limits our view of the cell inside the lorica (shell), and prevents us from seeing whether or not it has two flagella.
A fairly large particle is pushed around by diatoms
Various kinds of diatoms are swimming around this particle, and sometimes bump into it, forcing the particle to move.
Commentary by Prof. Yuji Tsukii, Hosei University There are a lot of similar-looking small diatoms. Therefore, to identify them by species, it is necessary to treat them with acid and compare the characteristic pattern of their cell wall using high magnification.
There is an organisms standing still in the upper-left of the video, with its contractile vacuole moving inside. From its body shape and the color of the chloroplast, it may be Cryptomonas or a related group.
The sample was observed immediately after being collected.
A large diatom is going in and out of soil aggregates. Small particles are moving inside of the diatom cell, and also a small unknown organism is moving behind it.
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to genus Surirella, probably Surirella robusta. It is often found in rivers.
The sample was observed immediately after being collected.
Four diatom cells are adhered to each other and standing still. Have they just finished dividing?
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to the genus Diatoma. After dividing, the two daughter cells don’t separate but remain adhered to each other by their valve faces, and develop into a colony. The colony consists of a row of connected individual cells showing their lined girdle faces. To identify the organism at the species level, it is necessary to observe the pattern of the valve face.
After being collected from a paddy field, the sample was put on 1% agar plate with a drop of distilled water and kept for a few days.
An oblong diatom is proceeding slowly and elegantly.
Commentary by Prof. Yuji Tsukii, Hosei University Identification of this diatom is difficult because only the girdle face of the cell is shown in this video. Without examining the pattern of the valve face, we cannot determine its species.
There are diatoms with a similar-looking girdle face. For example, a lot of Pinuularia can be found in the field.
After being collected from a paddy field, the sample was put on 1% agar plate with a drop of distilled water and kept for two days.
Two slender diatom cells are connected, perhaps after dividing, and are gliding around together.
Commentary by Prof. Yuji Tsukii, Hosei University Two diatom cells are connected side by side. Both cells show the girdle faces and only the right cell shows the valve face, from the latter the organism is assumed to be Pinnuralia.
The sample was observed immediately after being collected from a paddy field.
A light brown diatom is threading its way through soil particles. Without a specific organ for movement, how and by what mechanism does the diatom cell move around?
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to genus Pinnularia. When it glides on a surface, it usually shows the top view, called the valve face. However in this video, it shows the side view, called the girdle face. When the organism encounters particles in its path, it rolls onto its side to get through them.
The sample was observed immediately after being collected from a paddy field.
A diatom is traveling slowly through soil aggregates. Inside the cell, a lot of tiny particles are moving within the cytoplasm.
Commentary by Prof. Yuji Tsukii, Hosei University This organism is a diatom belonging to genus Surirella.
When diatoms glide, they usually show the top view, called the valve face. However, in this video, the cell shows the side view, called the girdle face. This organism is probably Surirella robusta or a related species.
The sample was observed immediately after being collected from a paddy field.
A diatom cell is slowly threading its way through obstacles.
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to genus Pinnularia. When it glides on a surface, it usually shows the top view, called the valve face. However in this video, it shows the side view, called the girdle face. When the organism encounters particles in its path, it rolls onto its side to get through them.
The sample was observed immediately after being collected from a paddy field.
A diatom cell is slowly threading its way through obstacles. Without a specific organ for movement, it is a mystery how the diatom moves around.
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to genus Pinnularia. When it glides on a surface, it usually shows the top view, called the valve face. However in this video, it shows the side view, called the girdle face. When the organism encounters particles in its path, it rolls onto its side to get through them.
After being collected from a paddy field, the sample was put on DNB agar plate (diluted nutrient broth with agar) with a drop of distilled water for 4 days, and then observed.
A large diatom cell slowly goes into and later backs out of a large aggregate. Long filamentous and rod-shaped bacteria are moving around. Some of the rod-shaped bacteria seem to gather around the rear of the diatom cell.
Commentary by Prof. Yuji Tsukii, Hosei University This diatom belongs to genus Pinnularia.
The organism is seen from the side view (girdle face), which does not show the pattern. We can’t be sure from this video whether or not the organism is in the process of division.
Flagellates vigorously swimming around are probably Trachelomonas volvocina.
