Characterization of swimming patterns of Vorticella, a model unicellular animal for microscale swimmers

Dilziba Kizghin Author

07/28/2020 Added

39 Plays

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A deeper look into the different swimming motions of Vorticella under 25 um

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[00:00:00.900]Hi, my name is Dilziba Kizghin and this summer
[00:00:03.829]I did my research in Dr. Sangjin Ryu’s lab on
[00:00:06.210]the characterization of swimming patterns of Vorticella,
[00:00:09.504]which is a model unicellular animal
[00:00:12.094]for micro-scale swimmers.
[00:00:16.298]Vorticella is a species of protozoa
[00:00:18.568]found in freshwater habitats like rivers and lakes.
[00:00:21.350]The cell is shaped like a balloon where
[00:00:23.150]it has a cell body and a stalk.
[00:00:25.689]When it’s sessile, it’s held in place by a stalk
[00:00:28.111]that it grows itself.
[00:00:30.021]Oral cilia are present on the cell body
[00:00:31.991]in both sessile and swimming forms.
[00:00:35.374]These cilia are tiny hairs that beat around
[00:00:37.544]to disrupt the water so it can feed
[00:00:39.328]on the small particles in the medium.
[00:00:42.246]Vorticella has been studied in its sessile
[00:00:44.366]form extensively because of its ultra-fast
[00:00:46.728]stalk coiling, but not in its swimming form
[00:00:49.153]which is when the stalk is cut.
[00:00:52.009]Most micro-swimmers usually are
[00:00:53.668]covered in cilia but as we can see,
[00:00:55.499]Vorticella only has cilia at one end,
[00:00:57.609]making its motions similar to a submarine.
[00:01:00.371]Therefore, Vorticella is a great model
[00:01:02.604]microorganism for micro-swimmers.
[00:01:05.480]The main goal of my project is to
[00:01:07.589]characterize the swimming motions
[00:01:08.904]of Vorticella confined between
[00:01:10.424]two parallel surfaces
[00:01:12.143]This goal was achieved by imaging,
[00:01:13.865]processing the images, and
[00:01:14.628]analyzing the result.
[00:01:19.413]For the methods in my research,
[00:01:20.373]I usually start from culturing cells and
[00:01:22.381]harvesting them.
[00:01:24.005]Harvested cells are allowed to
[00:01:25.335]grow their stalk again in a petri dish.
[00:01:27.643]When ready, the cells are scraped once more
[00:01:29.673]so that they will detach properly and
[00:01:31.289]swim freely.
[00:01:33.118]As seen in the figure on the left,
[00:01:35.238]the media with the swimming cells is then
[00:01:37.510]put onto a slide glass with 25 micrometer
[00:01:40.966]thick shims on each side and then sandwiched
[00:01:43.363]between another slide glass.
[00:01:45.657]I use this method to image the movement
[00:01:47.597]of cells in the two dimensional confinement.
[00:01:50.165]As seen in the picture on the right,
[00:01:51.788]the setup includes the inverted microscope
[00:01:58.903]Furthermore, a digital camera is connected
[00:02:00.883]to the microscope to take
[00:02:02.106]the images of the cells.
[00:02:03.924]For imaging, 4x magnification is used.
[00:02:06.074]If any larger magnification is used,
[00:02:08.007]cells are bound to swim out
[00:02:09.640]of the region of interest.
[00:02:11.395]This way, it’s easier to follow the cells
[00:02:12.888]as small particles when it comes
[00:02:14.443]to image processing.
[00:02:16.500]The frame rate of videos were taken
[00:02:18.352]at 24 frames per second,
[00:02:19.813]but during processing,
[00:02:21.129]it’s cut down to 12 fps.
[00:02:26.496]This is case one of cells under
[00:02:28.306]25 um confinement.
[00:02:30.079]This video is in 24 frames per second,
[00:02:32.642]twice as fast as compared to
[00:02:34.132]the original processed video.
[00:02:36.447]MATLAB was used to process
[00:02:37.941]this series of images and find the center
[00:02:39.607]of the cell, which is where we see
[00:02:41.084]the red star.
[00:02:42.654]The yellow part of the trajectory is
[00:02:44.204]the most recent part of the cell's
[00:02:46.153]movement, and the blue part indicates
[00:02:48.072]the path the cell has taken.
[00:02:50.658]If there were other particles
[00:02:52.098]in the region of interest
[00:02:52.871]like in this video here,
[00:02:53.524]background subtraction code was
[00:02:55.352]written so that only one cell
[00:02:56.802]was followed without noise.
[00:02:59.100]As we can see, the cell curves in
[00:03:00.730]and then has a circular repetitive
[00:03:02.610]motion with a larger radius.
[00:03:05.005]And then it tapers off into
[00:03:06.565]another direction while still
[00:03:07.919]in semi-circular or in other words,
[00:03:09.884]ballistic, motion.
[00:03:14.460]This is the processed data for case 1
[00:03:16.430]from earlier.
[00:03:17.740]In the swimming trajectory figure,
[00:03:18.930]we can see the movement of the cell.
[00:03:23.151]The swimming speed histogram shows
[00:03:24.561]that the cell’s swimming speed ranged
[00:03:26.322]from 50 to 200 um/s roughly,
[00:03:30.179]and its average speed was 110 um/s.
[00:03:34.541]It also appears to have multiple peaks,
[00:03:36.031]likely indicating to the fact that
[00:03:37.578]the cell maintains different speeds.
[00:03:40.500]The swimming direction histogram is
[00:03:41.800]somewhat uniform with a peak in the middle
[00:03:44.111]This is due to the constant direction
[00:03:45.691]change while the cell is circulating.
[00:03:48.510]The mean square displacement curve shows
[00:03:51.100]deviation of a cell with respect
[00:03:52.573]to a reference point as it swims around.
[00:03:55.980]The sinusoidal waves in the middle stand
[00:03:58.350]for the constant circulating motion of the cell.
[00:04:03.453]This video is the result of the
[00:04:04.823]second case for the 25 um confinement.
[00:04:07.988]The movement of the cell is very similar
[00:04:09.698]to case 1 where it is circular,
[00:04:11.278]but the radius of motion is much smaller
[00:04:13.492]and the speed also seems
[00:04:14.925]much slower in comparison.
[00:04:19.121]These figures show the
[00:04:20.011]processed data of case 2.
[00:04:21.974]It shows the cell’s trajectory under 25 um
[00:04:24.504]which is a tight circular motion
[00:04:26.611]with some noise.
[00:04:28.649]This noise is due to
[00:04:29.479]the cell’s slow speed and therefore,
[00:04:31.618]an overlap of the cell’s centroids
[00:04:33.663]from frame to frame when processing.
[00:04:36.741]That is why the general tightly circulated
[00:04:38.358]motion of the cell is true,
[00:04:39.886]but with some extra jagged lines.
[00:04:44.196]The swimming speed histogram indicates
[00:04:45.846]that the cell’s average speed
[00:04:47.196]was much slower compared to
[00:04:49.046]the previous case—a mere 21 um/s.
[00:04:54.038]The swimming direction histogram
[00:04:55.228]is quite uniform in distribution,
[00:04:57.176]meaning the cell’s directional
[00:04:58.558]circular movement was uniform.
[00:05:01.896]The mean square displacement curve
[00:05:02.896]shows uniform waves as time goes on,
[00:05:05.166]which is exactly what the cell does
[00:05:06.696]while swimming.
[00:05:11.673]This video represents the result of
[00:05:14.893]the third case under 25 um confinement.
[00:05:17.731]This particular cell moves in a similar
[00:05:19.931]fashion to the cell from case one, this is because
[00:05:23.373]the circular motion radius
[00:05:25.618]is larger compared to case 2.
[00:05:29.490]It has a somewhat uniform radius
[00:05:31.420]throughout and then towards the
[00:05:33.236]end of the video, it swims away to
[00:05:35.613]a different part of the region of interest.
[00:05:39.782]The cell’s speed also seems faster
[00:05:41.798]as compared to case 2.
[00:05:44.649]The cell also swims in a clockwise direction first,
[00:05:48.710]and then changes to a
[00:05:50.627]counterclockwise motion after a while.
[00:06:02.217]As we look at the analyzed data from
[00:06:03.857]from case 3, we see the trajectory of
[00:06:05.923]the cell—constantly circular
[00:06:07.355]and last-minute moves to
[00:06:08.660]a different part of
[00:06:09.928]the region of interest.
[00:06:16.051]The speed histogram is seemingly
[00:06:17.421]uniform with an average speed at 29 um/s.
[00:06:21.593]From this we can tell that the speed
[00:06:23.703]of the cell was overall not much faster
[00:06:26.005]but was more constant than case 2.
[00:06:30.270]The swimming direction histogram also
[00:06:32.100]indicates that the cell was swimming in a
[00:06:34.192]circular pattern with a slight increase
[00:06:36.109]in its radius and then abruptly changes
[00:06:38.225]its direction from circular to ballistic.
[00:06:41.336]The MSD curve of this case
[00:06:42.724]does not show the wavy pattern clearly
[00:06:44.454]although the cell showed
[00:06:45.924]circular trajectory.
[00:06:48.396]This is likely because of the last part
[00:06:49.926]of the trajectory, which is not circular.
[00:06:55.087]This summer I researched
[00:06:56.067]the trophont form of Vorticella,
[00:06:57.953]which is actually not the
[00:06:59.509]true swimming form.
[00:07:01.452]I analyzed the motion of
[00:07:02.302]trophont cells under 25 um confinement.
[00:07:06.051]The future of my research will include
[00:07:07.371]looking into different
[00:07:08.731]thicknesses of confinement
[00:07:09.601]with the trophont swimming form
[00:07:11.251]and comparing their differences
[00:07:12.974]and similarities.
[00:07:14.581]Furthermore, I will look
[00:07:15.896]deeper into the true swimming form
[00:07:17.226]of Vorticella.
[00:07:18.050]In the true swimming form of vorticella,
[00:07:20.220]or the telotroch form, the cell inverts
[00:07:22.347]its cilia from its oral area to the back area.
[00:07:26.012]This change alters the shape
[00:07:27.052]of Vorticella into a more tubular form.
[00:07:29.914]In this telotroch form,
[00:07:30.934]the cell is observed to swim
[00:07:32.354]much faster and cover more ground
[00:07:34.224]as opposed to the trophont form.
[00:07:37.243]During the next academic UCARE period,
[00:07:38.883]I will be comparing the swimming motions
[00:07:40.883]of vorticella under three different
[00:07:42.823]thicknesses as well as compare
[00:07:44.253]the movement differences between
[00:07:46.449]trophont and telotoch forms side by side.
[00:07:50.577]Thank you for listening,
[00:07:51.717]and have a good day.

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Characterization of swimming patterns of Vorticella, a model unicellular animal for microscale swimmers

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