Vorticella
The “Bell Animalcule”
Vorticella was observed by Leeuwenhoek in the early 17th Century and named by O.F. Mueller in 1786. Vorticella was also the first protozoan I witnessed as a young boy of ten through a small 100x power microscope. I was captivated when it instantly contracted its long stalk into a spring like coil, then slowly unwound to continue feeding. I sat transfixed watching it transform from a round blob into a beautiful bell with a crown of beating cilia, again and again it morphed. It was then that I understood how wonderful these protozoa really were, I was observing microscopic life in action. Several years later using a new more powerful microscope I witnessed their cilia beat in synchrony to produce two whirlpools or vortices, which brought a meal of bacteria and small protists to its “mouth”. Presumably why it is called Vorticella, and by its shape also the “Bell Animalcule”.
To this day Vorticella remains one of my special protists, what follows is a collection of images, videos and observations revealing some of the intricacies of this remarkable organism.
Vorticella – Order Peritrichida.
Vorticella adults are sessile and attached to the substrate by a fine contractile stalk. The main body has no somatic cilia, with the exception of the free-living teleotroch. The body is quite contractile using a myoneme system (Schroder 1906) and when stimulated will contract into a ball. The mouth leads into a peristomal funnel (Infundibulum) into which food particles are directed by the peristomal cilia wreaths which are counter clockwise. Food particles are directed down the infundibulum to cytoproct, then pinched off as food vacuoles (Images ….Video 1)
Taxonomy: The over 200 species so far described differ only in minute detail and often require special techniques to discriminate between them, including electron microscopy and genomics. (Kahal 1935, Noland and Finley 1931).
Phylogeny: Vorticella has a long ancestry. Recently fossil Vorticella have been discovered which are at least 250 million years old. They appear to be remarkably similar to extant vorticella and as can be seen in Plate 1, which shows a spirally contracting stalk. The stability of form over millions of years is a testament to an organism which evolved to occupy a niche in its watery environment. This is an elegant expression of form and function reaching perfection.
Plate 1: Recently discovered 250 million year old fossil Vorticella.
Video 1: Teleotroch detaching from the “mother ship”.
General Morphology:
Vorticella has a complex morphology, as shown in diagram 1. The following images illustrate the various cytological elements of vorticella.
• The “Bell”
• The Contractile Stalk
• The Teleotroch
• The “Bell” or body, is the cell of the Vorticella. It is covered by a pellicle which contains a number of elements including:
o The peristome with its cilia which comprise three counter-clockwise circlets leading into the Infundibulum, on to the Cytostome and onto the Cytopharynx from which the food vacuoles pinch off. (Plate 3, video …).
o A large sausage shaped meganucleus and associated micronucleus (Plate#)
o Contractile vacuoles
o Food vacuoles
o Mitochondria
o Cytoplasm
As the images demonstrate, Vorticella is a complex organism when compared to most metazoan cells, which are not independently functioning units, they are as the name implies part of a community of cells. It is interesting to visualise that momentous moment when unicellular organisms developed multicellular organisms as offspring. The general public perceives protists as “Simple Cells”, when in fact they are often functioning at the level of a “Simple Organism”. The fact is they are both our ancestors and our contemporaries.
Plate 2: Contractile vacuole.
Plate 3: Food vacuole being pinched off from the cytoproct.
PLATE 4: Vorticella sp with extended stalk note mitochondria on the spasmoneme.
PLATE5: Vorticella convallaria, Note the oblique myonemes, food and contractile vacuoles.
PLATE 6: Vorticella detached, note the sausage shaped meganucleus and undulating membrane in the peristomal funnel.
PLATE: Vorticella with attached mature teleotroch, which detatched 20 seconds later, see movie.
• The Contractile Stalk:
The metazoan muscle cell contracts utilizing Adenosine Tri-Phosphatase (ATP). After multiple contractions our muscle cells start to slow down, and finally cramp due to lactic acid build up. Ask any long distant runner who has hit the wall.
Vorticella’s stalk can contract again and again and never gets tired, add to that, it contracts about ten times faster than the metazoan myoneme cell.With that capability, Usain Bolt could run a one second 100 metres!
How does the Vorticella stalk achieve this? The answer lies in the world of biochemistry and biomechanics. First let us examine the structure of the stalk.
The stalk comprises several elements. The outer membrane is double and contains an inner contractile cord, the spasmoneme. Along the spasmoneme are small bodies which appear to be mitochondria, presumably to supply energy. (Image …..). The spasmoneme continues as a number of fibrils anchoring into the main cell. Recent research has described a method of contraction based upon Ca⁺ ions as energy input (rather than ATP), acting upon a series of sub-microscopic helical sliding plates.
Figure 1: Diagrammatic representation of Stalk (J.S. Douglas).
The Teleotroch and Encystation:
Vorticella can employ various survival strategies to overcome adverse conditions. It can detach from its stalk and “swim” feely as a teleotroch (image #), the teleotroch can then reattach to the substrate and secrete a new stalk. The teleotroch can also over time transform into a cyst.
Reproduction:
Vorticella undergoes asexual binary fission where a daughter buds off and leaves as a teleotroch (images 1-5 and video *), or it can undergo unequal binary fission, producing unequal microconjugants (Finley 1935). Sexual reproduction is by conjugation or autogamy (Finley in Kudo 1971).
Cultivation:
Vorticella can be found in most still water ponds, bird baths and such. Take some solid material and water from a bird bath or pond, add a few boiled rice grains, leave in a softly lit place and wait a week. The illumination will encourage filamentous algae to provide a substrate for the vorticella and the rice grains will promote bacterial growth as food. Subculture every two to three weeks.
Imagery acquisition:
All images were recorded using Olympus BX53 DIC research microscope, SC100 camera and Dimension Software. Unless otherwise stated no image processing has been carried out, other than basic brightness and contrast adjustment. All images are stamped with a scale in microns. Original full resolution images with meta-data are available upon request under the conditions described in this web site.
Conclusion:
Vorticella exemplifies the complexity which unicellular protists can attain, with a sophisticated peristomal ciliature to capture food, a contractile stalk utilizing a Ca+ based mechanism, strategies to survive adverse conditions, asexual and sexual reproduction, and an overall exquisite and beautiful structure with a 250 million year history.
Viva Vorticella.
References:
1. Klaus Hausmann, Protistology, E. Schwesizerbart’sche Berlin 2003
2. Richard Kudo, Protozoology, 5th Ed 1977,
3. Doris L. Mackinnon and R.S.J. Hawes, Oxford 1961