This ditch, at the periphery of Somenos marsh, is part of the new dike-and-drainage system completed about two years ago for flood control. Running parallel to a cornfield, it connects with the larger drainage system for lake overflow.
For a new system, it has quickly developed a flourishing system of water plants and algae that is somewhat different from that seen in the boat ramp on the lake proper a kilometer away. Areas of brownish and greenish algae dot the edge, and modest numbers of duckweed are present, but the water otherwise appears clear without the Anabaena bloom that affected much of the rest of the lake in the summer of 2015.
“Algae” that are not Algae:
Despite clear water and no Anabaena, the ditch is surfaced by islands of brownish-green, apparent algae; these are in reality mats of one of the many species of the cyanobacterium Cylindrospermum (see Algaebase reference), which under the microscope has an elegant curving pattern (thanks to Wim von Egmond for identification):
The ovoid structures are akinetes, or dormant cells; these thick-walled structures with dense cytoplasm are filled with food reserves and represent the survival mechanism for this algae-like, prokaryotic, photosynthetic bacterium. Akinetes can survive for years under dark and dry conditions, while the active vegetative cells die in a few weeks.
Cylindospermum appears to be distributed at least focally on all continents, appearing as mats in clean water, in soil or on water plants. It is the subject of some study at present, and species designations are being evaluated by cytogenetic analysis.
Note: Reading discussions on the evolution of life tends to make us think of “primitive” cyanobacterium/”blue-green algae” as organisms that existed long ago. It is important to remember that they are one of the most common life forms in the present day, thrive in every body of water, live happily within rocks and places thought inhospitable to life, form blooms off Fiji that can be seen from space, and travel to work with you every day in your car and lunch box.
(The University of New Hampshire’s Phytoplankton Key appears to be a good image-based identification tool for cyanobacteria.)
Algaebase. “Cylindrospermum.” http://www.algaebase.org/search/genus/detail/?genus_id=43595
Cyanodb. “Cylindrospermun.” http://www.cyanodb.cz/Cylindrospermum
Encyclopedia of Life. “Cylindrospermum.” http://eol.org/pages/11689/overview
Phytoplankton Key. “Cylindrospermum.” http://cfb.unh.edu/phycokey/Choices/Cyanobacteria/cyano_filaments/cyano_unbranched_fil/untapered_filaments/heterocysts/no_visible_sheath/CYLINDROSPERMUM/Cylindrospermum_key.htm
Wikispaces. “Akinetes.” http://cyanobacterianotts.wikispaces.com/Akinetes#Structure%20and%20Development
(Sanguinis: Just because you humans have Michelangelo and plastered this otherwise nice planet with a bunch of churches and pointy towers, you think that we “Lower” creatures have no sense of art! I tell you my ancestors could appreciate a nice swirl of algae when you were still painting yourselves blue. Just remember that it’s YOU that created Wal-Mart and Barbie.)
One ditch specimen contained a fascinating organism: Peranema. A not uncommon organism, Peranema has been studied for its method of locomotion, its feeding behaviour, and the fact that it responds to light by means of the same pigment found in our own retinas: rhodopsin. Though lacking chloroplasts, it is related to the green Euglena.
This video, taken from one York Road specimen, shows the use of Peranema‘s anterior flagella-like organelle. Note that this long organelle, which is considered more as an extended cilium than a true flagellum, is largely rigid in its basal segment and gives the impression of being used as much for exploration and sensing as for propulsion:
The use of this unique organelle has been described by Saranak and Foster as part of their investigation of light’s effects on Peranema‘s locomotion and the role of rhodopsin as a light-sensitive pigment (citation modified from original article):
“Peranema trichophorum is a colorless eukaryotic phagotroph of the Euglenophyta that lives in fresh water. It does not have a chloroplast but rapidly deforms in shape and is very effective at capturing and eating prey . Peranema voraciously takes any particles into its body by phagocytosis . This “feeding behavior” is clearly and commonly observed under the microscope. Its life cycle is not well studied. …cells….are seen to glide forward on a surface pulled by their leading anterior cilium, which is about the length of the cell body. (We use the word “cilium” rather than “eukaryotic flagellum” to describe the leading appendage that enables the cell to glide to emphasize that this appendage is not the more familiar rotary motor-driven flagellum of bacteria. The cilium controls linear motors that slide microtubules relative to each other in the axenome and is the same as the cilia of Ciliata. This choice of terminology follows the advice of….Manton and….Cavalier-Smith, who says “the word flagellum should be dropped altogether from eukaryotic biology.”)
….mature cells are pulled forward along a surface by the cell surface motility of the proximal five-sixths of the anterior cilium. The cilium is straight except for the waving anterior one-sixth, which presumably senses particles of food and obstacles (my italics). A second thinner cilium runs posteriorly and tightly appressed to the cell body, lying between the cell body and gliding surface, and is rarely visible under the light microscope. Apparently, the thin cilium does not participate in driving the cell forward. The cells are in sufficient contact with the surface to not rotate as they glide. In order to turn, the cell body curves and then straightens with its cilium pointing toward its new direction. The cells also curl their bodies into a ball, with fast beating and waving of their cilia, when they eat…..
Mature Peranema cells glide, turn, and curl spontaneously in either light or dark. A movie of the curling can be seen at the Euglenoid Project website (http://www.plantbiology.msu.edu/triemer/Euglena/movies.htg/peranem2.mov). As originally noted by Shettles, the frequency of curling behavior is apparently enhanced by an increase in light, as shown by a shortening of the time before the next curl. Shettles mapped the location of photosensitivity to the primary cilium and the front half of the body.
…we used our established techniques for the identification of photoreceptors to show….that rhodopsin is indeed the photoreceptor for the curling behavior of Peranema. We also….link rhodopsin activation to calcium ions and channels during curling behavior….”
Wikipedia has an excellent general description of Peranema’s feeding behavior:
“The cell is spindle or cigar-shaped, somewhat pointed at the anterior end. It has a pellicle with finely-ridged microtubules (a structure often referred to as “pellicle strips”) arranged in a helical fashion around the body … the spiraling microtubular strips are able to slide past one another, giving the organism an extremely plastic and changeable body shape. This permits a type of squirming motility, sometimes referred to as “Euglenoid movement” or metaboly…. When it is not swimming, Peranema can creep along by metaboly, progressing with wavelike contractions of the body, reminiscent of peristalsis.
At the anterior of the cell, there is a narrow aperture, opening into a flask-shaped “reservoir”, from which the organism’s two flagella emerge. At the bottom of this reservoir lie the basal bodies (centrioles) to which the flagella are attached. One flagellum is relatively long and conspicuous, and when the Peranema is swimming it is held stiffly in front. At the tip of the flagellum, a short segment beats and flails in a rhythmic manner, causing the Peranema to move forward through the water with a calm, gliding motion. Peranama usually swims belly-down, without rotating.
The second flagellum is difficult to see with bright field microscopy, and was entirely overlooked by early observers. It emerges from the same reservoir as the larger propulsive flagellum, but turns toward the posterior. It does not float freely, like the trailing flagella of Dinema and Entosiphon, but adheres to the outside of the cell membrane, in a groove along its ventral surface.
Next to the reservoir, lies Peranema’s highly developed feeding apparatus, a cytostomal sac supported on one side by a pair of rigid rods, fused together at the forward end. The use of this “rod-organ” in feeding has attracted considerable scholarly interest. Some early researchers speculated that it might assist Peranema in tearing up and consuming its food; while others held that it was actually a tubular construction, serving as a cytopharynx. In 1950, Y. T. Chen accurately identified it as a structure separate from the reservoir, which could be used by Peranama to cut and pierce its prey … Nisbet questioned this, on the grounds that, when examined closely with an electron microscope, the rod-organ is blunt, and therefore an improbable instrument for either cutting or piercing. Since the rod-organ had been seen to move back and forth during feeding, Nisbet argued that its primary function is to create suction, drawing prey into the cytostome.
In 1997, Richard Triemer returned to the subject, to confirm Chen’s opinion that Peranema has a dual feeding technique. It can swallow prey whole, pulling large flagellates through the cytostome, in a manner similar to that proposed by … Nisbet. However, it can also choose a more elaborate style of attack. Sometimes, it will press its cytostome against its prey, and then move the rod-organ up and down, using a rasping motion to chew a hole in its victim’s cell membrane. After consuming some of the protoplasm, the Peranema may then insert its large flagellum into the hole, using it to churn up the contents of the cell so that they may be more easily sucked out. This continues until nothing is left of the prey…”
So much to learn from a teaspoon of ditch water!
Encyclopedia of Life. “Peranema trichophorum.” http://eol.org/pages/897916/overview
Saranak, J. and Foster, K.W. “Photoreceptor for Curling Behavior in Peranema trichophorum and Evolution of Eukaryotic Rhodopsins.” Eukaryot Cell. 2005 Oct; 4(10): 1605–1612. Online as: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1265905/
Wikipedia. “Peranema.” https://en.wikipedia.org/wiki/Peranema.