I’m torn here. On the one hand, this is really cool. On the other, it somehow feels horribly wrong. I mean I’m sure it’s not much more wrong than what I do to baker’s yeast every time I bake bread. But . . . I don’t toy with the yeast before I incinerate them. Yeesh.

Anywho, for those who are unfamiliar, paramecia are classic organisms used to teach high school and college students about microbes. But they’re not simply boring microbial lab rats. They’re fascinatingly formed, filled, and operated little creatures. They are often described as “slipper-shaped”, or, as van Leeuwenhoek would have it, “slipper animalcules”. In this video, watch for the little cilia beating all over the cell’s pellicle, or membrane+submembrane shell.

So let’s have a tribute to the humble Paramecium today — we’ll take a closer look at a microbe you might think you already know. Think again. Take a look at the basic paramecium formula here (I can’t post it because I don’t have copyright). I’ll refer to the various parts of this diagram as we go along.

Paramecia are ciliates, protists coated in little beating hairs called cilia for at least part of their life cycle. In photographs where only their cilia are stained or photographed with scanning electron microscopy, paramecia look like ovoid shag rugs (or see here or here). These cilia can beat in forward or reverse with extreme precision — much more precise than large flagellae or lumbering pseudopods. When beating in foward or reverse, the paramecium moves in a spiral motion around an invisible axis — and they can throw it into reverse in a ciliumbeat to avoid obstacles or “negative stimuli” (cough).

Inside the cell is a contractile vacuole used to bail out water against the perpetual osmotic gradient (the inside of the cell has a higher solute concentration than its watery surroundings, leading water to constantly seep through the membrane by osmosis, like a leaky ship), various vacuoles (spherical storage vessels) for digesting food and excreting waste, and at least one micronucleus and macronucleus.

The micronucleus, of which there may be as few as one or as many as 80, is diploid, or contains two copies of all the DNA, just like all of your cells. But the macronucleus may contain 50-500 times as much DNA as the micronucleus (the Paramecium aurelia macronucleus is 860-ploid, according to one of my biology texts). The micronucleus is all about passing DNA to mating partners for sexual reproduction (aka swapping genes), while the macronucleus is in the business of pumping out messenger RNA and getting it translated into proteins.If you remove the micronucleus, the cell can divide asexually another 350 or so times before dying of no sex (yes, in ciliates, this can apparently happen). But if you remove the macronucleus, the cell immediately dies.

On the surface of the cell is a funnel-shaped oral groove that guides food particles toward a pocket where food vacuoles are created. Enzymes get pumped inside to digest whatever hapless bacteria, yeast or “other” finds its way inside. Many paramecia may contain symbiotic bacteria living within them or even within their macronucleus, perhaps providing vitamins or other growth factors that would otherwise be hard to get. One paramecium even has photosynthetic symbionts. Paramecium bursaria, which has ingested and partnered with the green alga Zoochlorella.

These are *not* chloroplasts, or rather, they are not homologous to (share a common ancestry with) the chloroplasts in plants. Plant chloroplasts are ingested cyanobacteria. Zoochlorella are chloroplasts in the sense that they are internal photosynthetic symbionts, but they were free-living eukaryotic (nucleated — not bacterial) algae before ingestion. But here’s the mind-twister: the chloroplasts within the Zoochlorella are homologous to plant chloroplasts, because plants evolved from green algae.
This is the only Paramecium known to do this. To what extent the Zoochlorella could pop out of that paramecium and get along on its own or is degenerate and helpless I do not know.

Paramecium bursaria, a rare symbiotic photosynthetic paramecium. Love the gorgeous detail. Creative Commons PROYECTO AGUA**/**WATER PROJECT

Some large ciliates may hold the land-speed record for all protists. They can cruise at a blinding 2 millimeters per second, which, assuming a 250-micrometer paramecium and a 5.5-foot human [calculator tapping noises], is the equivalent our 5.5-foot human swimming  a blazing 30 miles per hour*. And they are backstroking at these speeds through a medium that has the viscosity (to a proist) of molasses.(See the middle of Psi Wavefunction’s post here, or for the physics-buff bionerds out there, the original 1977 paper “Life at [a] Low Reynolds Number” here).

Paramecia are also armored with a built-in defense system. Their pellicle is laced with dart-tipped harpoon-esque “trichocysts” (a specific type of a more general organelle called an “extrusome“, which is clearly another case of convergence (independent invention of the same structure) with jellyfish nematocsyts), which deploy explosively within milliseconds if the paramecium feels threatened, is feeling peckish, or perhaps needs a convenient anchor while it tucks in to dinner. See how they look retracted here, and how they look once fully-expelled here, which this site describes as the “disheveled porcupine” look. The bottom photo is of undeployed trichocysts in the pellicle**.

Known diversity in ciliates, ca. 1904, by the incomparable Haeckel

Paramecia are, as mentioned, ciliates. There are something like 9,000 species in fresh and salt water, and their complexity and diversity of form is astounding. Some of the most complex species come close to replicating the digestive systems, muscles, exoskeletal systems and even vertebrae so characteristic of multicellular life within a single cell. According to one of my biology texts, ciliates have produced the greatest specialization of subcellular organelles of any protist. Rest assured you will read more about the creatures in this group at this blog.

Ciliates fit into the larger taxon (group) called alveolates, a term you may recognize from high school biology as the name for the little sacs at the ends of the passages of your lungs. The structures are similar; the Latin just means “little cavities”, and in ciliates like Paramecium they are little membranous sacs found just below the cell surface engulfing the roots of cilia. Though the ciliates like Paramecium and the dinoflagellates and parasitic apicomplexans may seem worlds apart, they all share this feature and several others*** that reveal their common ancestry. See how the ciliates fit into the alveolates, and how the alvaeolates fit into the eukaryotes here and here.

Before I leave you today (or is it the other way around?), enjoy this video of some more active paramecia tooling around with a bunch of nerdy Euglena (the little guys). Because before you allow your little microbial minions to be devoured by Pac-Mecium or taunt them with a chemical blast, remember: were they your size (or you theirs), you’d never survive the hairpin extrusome assault mechanism, and they’d be gone before you knew what hit you. : )

________________________________________________
*or 48 km/hr for you metric users. According to the intertubes, the fastest human swimmers can go is around 5 miles/hr over very short distances. Of course, their bodies are not covered in highly-efficient propulsive cilia (and more’s the pity).

**With all this weaponry, forget Pac-mecium. Helloooooo Ultimate Paramecium Fighting League.

***including, for the bionerds out there, tubular mitochondrial christae, “closed mitosis” in which the micronuclear membrane doesn’t dissolve during mitosis and the mitotic spindle forms inside it, and similar “extrusive organs” like trichocysts

Want to know what this exciting cilia action is all about? Then head on over to the Scientific American Guest Blog, where (here’s my exciting news) my first invited post was published today! Yay! They even honored my request to allow you to click to embiggen (as fellow Boulderite Phil Plait would say) the art. Hope you enjoy.

Diatoms: What Would Result if the Japanese Could Design their Own Microorganisms. These guys are screaming for a collector card set. Image by Rovag, Creative Commons Atribution 3.0 Unported License. Click for link.

Earlier this week I posted a link to Victorian microscope slides that included arranged diatom art. People really seemed to respond to the diatom image I posted with it, so I wanted to talk a little bit more about what diatoms are and a lot about their amazing shells. Diatoms literally live  in glass houses, and as you can imagine, that makes sex, growth, and buoyancy a tricky business. How do you have sex when you live in the architectural equivalent of a microscopic  petri dish? As they say — very carefully.

Schematic of diatom frustules. (A,B) Centric Diatoms. (A) girdle view, (B) valve view. (C,D,E) Pennate Diatom. (C) broad view, (D) valve view, (E) narrow girdle view (transverse section). Cupp, E.E. (1943). Marine Plankton Diatoms of the West Coast of North America. Bull. Scripps. Inst. Oceanogr. 5: 1-238 Image by Matt-eee, Creative Commons Attribution 3.0 Unported License. Click for link.

Notice that the sperm have flagella that point *forward*. Those are the tinsel flagella, that pull the cell behind them. Image by Matt-eee, Creative Commons Attribution 3.0 Unported license

Hey, baby, wanna swap nuclei? The life cycle of the pennate (not-radial) diatoms. Image by Matt, Creative Commons Attribution 3.0 Unported License. Click for link.

NOTE: Correction below.

Well, this brings new meaning to the concept of gilled mushrooms. Scientists have stumbled upon the first mushroom that fruits underwater, as proudly displayed on the cover of this month’s Mycologia. Notice the little bubbles on the outside of the mushroom. On aquatic plants (like the moss to the left), bubbles form because the plant is producing oxygen via photosynthesis. On the mushroom, the bubbles are probably the product of respiration, which means they are filled with CO2, not O2, as the mushroom “breathes”.Yes, fungi burn sugar with oxygen to produce energy and CO2 just like we do, but you can see it here because the fungus is underwater*. Way cool! (CORRECTION: HeyPK points out in the comments that CO2 is highly soluble in water (true — at 20C in freshwater, the solubility limits are 1.45 g/L for CO2 vs. 9 mg/L for O2) so the bubbles are more likely more oxygen bubbling out of the supersaturated stream using the mushroom as a substrate much the way the CO2 in carbonated beverages comes out of solution on ice in glasses. Oops! Sorry for the mistake readers — I’m still learning too. I’m sure I’ll make more from time to time despite my best efforts so please do help me fix them when you see them and I will post a prompt correction. : ) )

According to the good folk over at MycoRant, where I discovered this, scientists had never looked for mushrooms underwater before, but that didn’t mean they weren’t there. Brit Bunyard, editor of Fungi, speculates there may be a whole world of aquatic mushrooms out there we didn’t know about because we never really looked. If so, he noted at MycoRant, it would not be the first time that happened.

The mycologist Cecil Terence Ingold (who as of last year was still alive at the age of 104) stumbled upon an entire world of virtually undescribed fungi living in ephemeral forest pools and trickling streams:

In 1937 Ingold moved to University College, Leicester, where he “became excited by the chytrids attacking planktonic algae”.  It was his discovery of one particularly beautiful such chytrid (Endocoenobium eudorinae) that reportedly caused him to specialize thereafter in mycology rather than plant physiology; and the next year, while searching for chytrids in a small brook near his home, he found in the stream scum an “abundance [of] many kinds of most extraordinary fungal spores”, most of which were large and tetraradiate in shape.  For several months he continued to find such spores in scum, and he finally discovered their source to be fungi living on submerged alder leaves in the stream bed.  He later learned that a few such fungi had been described earlier, but, he thought, “rather inadequately”; and so he undertook to classify those aquatic hyphomycetes into eight new genera, all of which remain valid today.

They are sometimes called the “Ingoldian Fungi” in his honor. The incredibly beautiful spores of these fungi (often called amphibious or aero-aquatic fungi or aquatic hyphomycetes), in addition to being star-shaped, whorled, knobbed, or otherwise tricked out in the most wonderful fashion, are hollow when found in still pools — so they can float and get first crack at the ecosystem’s power source: leaves that have just dropped to the water’s surface.

Dear readers, there’s a whole crazy world of living things out there, often invisible to the naked eye but fabulous beyond belief, even in an otherwise unexciting-looking puddle in the forest outside your door. All we have to do is look.

_____________________________________________________________________

*And by the way, the gills in mushrooms are for maximizing the spore-making surface area, not for maximizing the gas-exchange surface. Most mushrooms are small enough the CO2 just diffuses out passively (giant puffballs notwithstanding).