Frog feet

A few days ago, a colleague of mine asked me how biologists decide which microalga is their favourite. (She’s a physicist, I guess these strange people have favourite equations or something.)

That got me thinking. What’s the coolest microbial species?

Of course, the answer will depend on who you ask, because the notion of “cool” is subjective. Yet, here I propose some criteria to try and identify potential contenders for the title.

1) A funny name

Binomial latin names are designed to unambiguously identify species. But they can be more than that.

Frequently, they provide a useful (yet rather unimaginative) indication to what the beast looks like (Physeter macrocephalus has a big head), where it comes from (Sonchus canariensis grows on a specific Atlantic archipelago), or what it tastes like (Boletus edulis is good for you, when Rubroboletus satanas isn’t).

Names of marine microbes also follow this pattern : Mesodinium rubrum is red, Dinophysis acuta is pointy, Dinophysis acuminata isn’t but for some reason its descriptors wanted you to believe it was.

Sometimes though, you get something much more creative, and arguably funnier. Behold Ceratoperidinium yeye, named so by Margalef in 1969 because its long “legs” reminded him of dancers of the Yé-yé music style¹.

Sadly for Ceratoperidinium yeye, a killjoy taxonomist renamed it to Ceratium margalefii a few years later because the original description was not made properly (Margalef should have written a morphological description in Latin and not only in Spanish). Still, Ceratoperidinium yeye lives in my heart, and now in yours.

2) A striking appearance

It’s easier to be remembered when you stand out of the crowd in the phytoplankton sample. I guess it’s unfair (that’s basically the microbial version of charismatic species), but it is what it is.

As far as looks go, diatoms often steal the show. Not all microalgae can measure up to a cathedral’s rose window :

Coscinodiscus even had its moment of fame a few years ago. In 2021, the excellent John Dolan (from the Villefranche oceanographic lab) tweeted a photo of Coscinodiscus bouvet that, unbeknownst to him, vaguely resembled the logo of the K-pop band BTS. His tweet got thousands of likes from enthusiastic K-pop fans in just 4 days.

3) The ability to do something weird

In biology, we like creatures that venture off the beaten track.

Mesodinium hijacking the nucleus of its prey to make photosynthesis although he’s not a “real” microalga? Ciliates relying on a different genetic code than virtually everyone else? Albino orchids stealing carbon from nearby trees via an underground fungi network? Definitely cool. I want to study that².

Lacrymaria olor is a ciliate that extends its “neck” 30 times its body length to hunt prey, in a matter of seconds. It does that by folding and unfolding its cytoskeleton like origami:

Does microbiology get any cooler than that? Lacrymaria olor moves like crazy, looks awesome and its name means “swan teardrop”, ticking all 3 criteria.

I’d like to introduce another contender though. It is, of course, a dinoflagellate.

My pick for coolest microbe

Have you ever heard of Ceratium ranipes?

Ceratium³ is a dinoflagellate genus beloved by phytoplankton taxonomists. Ceratium cells present 3 “horns” that protrude from the cellular body, giving them an unmistakeable look. They come in a wiiiiiide variety of shapes, and entire taxonomic monographs are dedicated to them.

Ceratium ranipes though, is unusual even among Ceratium. Sometimes, it looks like a “classic” Ceratium, and sometimes, it bears “fingers” at the tip of its antapical horns. This understandably puzzled phytoplankton taxonomists, who described several morphotypes of Ceratium ranipes showing more or less fingers, or none at all. See for yourself:

For decades, there was no clear explanation for why different morphotypes existed. In 2009 however, a team of planktologists from the Villefranche oceanography lab made a striking discovery: they found that individual Ceratium ranipes cells grow fingers in the morning and retract them at dusk.

During the day, C. ranipes cells display long fingers filled with chloroplasts and do not move much, photosynthesising as much as they can. At night, fingerless cells activate their flagella and roam the planktonic world.

The ecological advantage conferred by this diurnal change in morphology is not completely explained. Cells with fingers appear to sink slower than their fingerless counterparts (because fingers confer a higher surface/volume ratio), so this could help C. ranipes to position itself in the water column: near the surface during the day for photosynthesis ; and deeper during the night to replenish nutrient reserves, or to escape nocturnal predators that feed in the upper layer.

These slender fingers give Ceratium ranipes a really peculiar look, almost clumsy, that makes it pop out among all other dinoflagellates. They also gave it its rather charming name: ranipes means “frog feet”.

So here’s my pick for coolest microbe! You may disagree, and if so I’d be delighted to know the one you would have chosen (the comments section is here for that!) But I can rest easy, because the acknowledgements section of Pizay et al.‘s paper reassures me that I’m not the only one thinking that C. ranipes is “totally cool”!

I’d like to dedicate this post to John R. Dolan (alias Tintinnidguy). Your contagious passion for protists is one of the reasons that drove me towards studying them, so thank you Dr. Dolan!

Speaking of the Villefranche oceanography laboratory, I can only recommend visiting the aquaparadox website, which is a goldmine for protists enthusiasts (amazing image gallery, old taxonomy monographs…) Many illustrations in this post come from there. Also, the great Pizay et al. (2009) paper can be accessed there, unpaywalled (bottom of the page –> Products).

Finally, if you want to see Ceratium ranipes in motion, you can watch this episode of Plankton chronicles!

Bibliography:

Yue Jiang, Yuxin Peng, Hyeon Ho Shin et al. Characterization of Gymnodinialimonas ceratoperidinii gen. nov.,sp. nov., a New Bacterium Isolated From Rare Marine Dinoflagellate Ceratoperidinium margalefii (2021) PREPRINT (Version 1) available at Research Square https://doi.org/10.21203/rs.3.rs-1126159/v1

Dolan, John. “When A Diatom is Adopted by K‐pop Fans—the Story of an Accidental Outreach Hit.” Limnology and Oceanography Bulletin 30.3 (2021): 97-97. https://doi.org/10.1002/lob.10453

Eliott Flaum and Manu Prakash “Curved crease origami and topological singularities at a cellular scale enable hyper-extensibility of Lacrymaria olor” bioRxiv 2023.08.04.551915 (2023): doi: https://doi.org/10.1101/2023.08.04.551915

Pizay, Marie-Dominique, et al. “Night and day morphologies in a planktonic dinoflagellate.” Protist 160.4 (2009): 565-575. https://doi.org/10.1016/j.protis.2009.04.003

Several illustrations in this post are not my own work, and are possibly subject to copyright. I credited the author(s) below each illustration. The text in this post is under a CC BY 4.0 license.

1. I need to point out that, as far as I can tell, this origin of the name is not stated by Margalef in its original description. I know I’ve read it somewhere but can’t find it anymore. Given the date, this etymology makes sense, so I’ll leave it here unless somebody points out that I’m wrong. ↩︎
2. Additional tip: if your favorite microbe happens to produce toxins that cause diarrhea from hell, you’re more likely to get funding to study it. ↩︎
3. I have to say that the taxonomically correct name for marine Ceratium species has been changed in 2013 and is now Tripos, with Ceratium being reserved for freshwater species. I’ll stick with Ceratium, because it is much nicer, and for coherence. ↩︎