Rotifers!

 How the Bdelloid Rotifer Lived for Millennia—Without Sex

by Nina Munteanu 

 

As a child, I always wanted a microscope.

I would have collected slimy waters from the scum ponds and murky puddles near my house. I would have brought them home and exposed them to the light of my microscope. I would then have peered deep into a secret world, where shady characters and alien forms lurked and traded.

It would be many years, when I was in college, before I finally witnessed this world—so alien, it might have inspired the science fiction books I wrote later as an adult. As it turned out, I was led to pursue a Masters of Science degree, studying periphyton (microscopic aquatic communities attached and associated with surfaces like rocks and plants) in local streams in the Eastern Townships of Quebec.

While my work focused on how diatoms (glass-walled algae) colonized surfaces, micro-invertebrates kept vying for my attention. Water fleas (cladocerans), copepods, rotifers, seed shrimps (ostracods) and water bears sang across my field of vision. They flitted, lumbered, wheeled and meandered their way like tourists lost in Paris. But this wasn’t Paris; I’d taken the blue pill and entered the rabbit hole into another world...

 

The Secret—and Dangerous—World of Micro-Organisms

Small freshwater habitats are home to a highly productive and diverse collection of micro-invertebrates—multicellular animals that can barely be seen with the naked eye. Many average from 0.5 to 1 mm in size and resemble little white blobs; however, a scholar can distinguish each invertebrate by its unique movement. For instance, when presented with a jar of pond water, I can usually distinguish among the wheel-like wandering of a gastrotrich, dirigible-like gliding of an ostracod (seed shrimp), the vertical goldfinch-style “hopping” of the cladoceran (water flea) as it beats its antennae, or the halting-jerking movements of copepods (oar-feet) as their antennae drive them along like a dingy propelled by an amateur oarsman.

Alas, puddles, ephemeral ponds and vernal pools pose sketchy habitats, given their tendency to appear and disappear. These environments are ever-changing, unstable, chaotic and unpredictable. Yet, anyone who has studied these ecosystems understands that they team with life.

When a puddle or ephemeral pond dries up then reappears with rain, how can these communities thrive? Do they all die off and then somehow recruit when the pond reappears? Many of these invertebrates have evolved creative ways to survive in very unstable environments. Some form a resting stage—a spore, resting egg or ‘tun’—that goes dormant and rides out the bad weather.

Animalcules & Sleeping Rotifers

Rotifers are cosmopolitan detrivores (they eat detritus) and contribute to the decomposition of organic matter. Rotifers create a vortex with ciliated tufts on their heads that resemble spinning wheels, sweeping food into their mouths. They often anchor to larger debris while they feed or inch, worm-like, along substrates. Some are sessile (attached), living inside tubes or gelatinous holdfasts and may even be colonial. Others move about and may temporarily anchor themselves as they feed. Rotifers include species that alternate sexual reproduction with asexual reproduction, depending on environmental conditions.

Bdelloid Rotifer as photographed by Bob Blaylock

In 1701, Antonie van Leeuwenhoek observed that “animalcules” (likely the bdelloid rotifer Philodina roseaola) survived drying up and were “resurrected” when water was added to them. He’d discovered a highly resistant dormant state of an aquatic invertebrate to desiccation.

Dormancy is a common strategy of organisms that live in harsh and unstable environments and has been documented in crustaceans, rotifers, tardigrades, phytoplankton and ciliates. “Dormant forms of some planktonic invertebrates are among the most highly resistant … stages in the whole animal kingdom,” writes Jacek Radzikowski in a 2013 review in the Journal of Plankton Research. Radzikowski describes two states of dormancy: diapause and quiescence.

Diapausing results in the production of a dormant egg or cyst whose thick envelope or shell protects it from drying, freezing, mechanical damage, microbial invasion and predation, UV radiation and harmful chemicals. Many survive being eaten and can resist vertebrate digestive enzymes, helping them disperse and colonize isolated water bodies. Diapause is controlled by an internal mechanism that is initiated by various cues, such as temperature or photoperiod. In short-lived organisms, it is typically initiated only in a single ontogenetic stage. “Breaking of diapause requires specific cues, and not necessarily the return of favorable conditions,” writes Radzikowski.

Quiescent dormancy does not involve the production of a dormant egg or cyst; rather it involves a transformation of the organism itself into a dormant state through a process called cryptobiosis. “Quiescence is … induced directly by the occurrence of harsh environmental conditions. A quiescent organism can enter this state in many stages of its life, and remains dormant only until the adverse conditions end,” writes Radzikowski.

The All-Female Bdelloid Rotifer

I recently had a chance to study a pond sample in a Petri dish through a friend’s microscope. Attached to a pile of detritus shivering in the current like trees in a gale, were several microscopic rotifers; they were feeding. Their ciliated disk-like mouths twirled madly, capturing plankton to eat. Watching them reminded me of my early research days at Concordia University in Montreal. Probably Philodina (a bdelloid); I had seen many during my stream research in Quebec.

The bdelloid rotifer has dispensed with sexual reproduction entirely and reproduces exclusively by female parthenogenesis. All-female bdelloid rotifers have thrived for forty million years. They’re everywhere, in temporary ponds, moss, even tree bark. Part of the reason for their incredible success lies in their strategy of quiescent dormancy.

In response to unfavourable conditions like a pond drying up, bdelloid rotifers enter a process called anhydrobiosis, contracting into an inert form and losing most of their body water. The bdelloid withdraws her head and foot and contracts her body into a compact shape called a tun; a dormant state that remains permeable to gases and liquids. In this state, bdelloid rotifers can resist ionizing radiation because they can repair DNA double-strand breaks. Early research noted that dormant animals could withstand freezing and thawing from −40°C to 100°C and storage under vacuum. They also tolerated high doses of UV and X radiation. Later work reported that some rotifers could survive extreme abiotic conditions, such as exposure to liquid nitrogen (−196°C) for several weeks or liquid helium (−269°C) for several hours. Dried up adult bdelloid rotifers apparently survived minus 80°C conditions for more than 6 years.

Dormancy is an elegant technique to ride out harsh conditions. The bdelloids can go dormant quickly in any stage of their life cycle—embryo, juvenile or adult—and they’re capable of remaining dormant for decades. They can recover from their dormancy state within hours when the right conditions return and go on reproducing without the need to find a mate.

Research has shown that bdelloid mothers that go through desiccation produce daughters with increased fitness and longevity. In fact, if desiccation doesn’t occur over several generations, the rotifers lose their fitness. They need the unpredictable environment to keep robust. This is partly because they incorporate genes from their environment during anhydrobiosis. When dormant, they acquire mobile DNA and stitch it into themselves through a process called horizontal gene transfer (HGT).

Bdelloid rotifers carry change inside them, through phenotypic plasticity, physiological stress response mechanisms, or life history adaptations. That’s why the bdelloid rotifers survived for millennia and will continue for many more. They are able to keep up with rapid and catastrophic environmental change, not to mention something as gigantic as climate change. They adapt by counting on change.

References:

Munteanu, Nina. 2020. “A Diary in the Age of Water.” Inanna Publications, Toronto. 300pp.

Munteanu, Nina. 2016. “Water Is…The Meaning of Water.” Pixl Press, Vancouver. 586pp.

O’Leary, Denise. 2015. “Horizontal gene transfer: Sorry, Darwin, it’s not your evolution anymore.” Evolution News, August 13, 2015. Online: https://www.evolutionnews.org/201508/horizontal_gene/

Ricci, C. And D. Fontaneto. 2017. “The importance of being a bdelloid: Ecological and evolutionary consequences of dormancy.” Italian Journal of Zoology, 76:3, 240-249.

Robinson, Kelly and Julie Dunning. 2016. “Bacteria and humans have been swapping DNA for millennia”. The Scientist Magazine, October 1, 2016. Online: https://www.the-scientist.com/?articles.view/articleNo/47125/title/Bacteria-and-Humans-Have-Been-Swapping-DNA-for-Millennia/

Weinhold, Bob. 2006. “Epigenetics: the science of change.” Environmental Health Perspectives, 114(3): A160-A167.

Williams, Sarah. 2015. “Humans may harbour more than 100 genes from other organisms”. Science, March 12, 2015. Online: http://www.sciencemag.org/news/2015/03/humans-may-harbor-more-100-genes-other-organisms

I wrote an illustrated book - about invisible stuff!

By Claire Eamer

Cover art by Marie-Eve Tremblay.
Published by Kids Can Press.

My latest kids' science book - Inside Your Insides: A Guide to the Microbes That Call You Home - hits the bookstore shelves on Tuesday, September 6. And I'm thrilled.

I know, I know - I've been here before. After all, this is my seventh kids' book. But the launch of a new book never loses its charm. There's a long and sometimes painful road from the first exciting bit of research to the finished object - all shiny and glossy and colourful, and just waiting to delight fresh eyes.

This time there's an extra level of delight, at least for me. The topic of the book is the invisible menagerie of tiny critters that make up the human microbiome. The key word here is "invisible." And a key aspect of kids' books is illustration. So, how do you illustrate the invisible?

One solution might have been photographs. Microbes aren't really invisible - just really, really small. You can see some of them through a light microscope and more through an electron microscope, but some are barely visible even with the best equipment. And they....well....they look a bit boring. (Sorry, microbiologists! I know you love them all.)

EHEC bacteria, O104:H4 outbreak strain. Scanning electron microscopy. Bar: 1 µmSource: Gudrun Holland, Michael Laue/RKI

The better solution is an artist - in this case, the marvellous Quebec artist and illustrator Marie-Eve Tremblay.

I should explain that the publisher, Kids Can Press, came up with this solution. I just sent them words and then sat back and crossed my fingers, hoping they'd find a way to bring the book to visual life.

And they certainly did. Marie-Eve's microbes have character, humour, colour, emotion. Not bad for mostly-single-cell organisms. They might not be exactly what a microbiologist sees, but they get some fairly difficult information across in a way that will engage the kids reading the book.

And, who knows? Some of those kids might be the next generation of microbiologists. I hope so!

Thanks, Kids Can Press and Marie-Eve Tremblay, for making my words come to colourful and entertaining life.

If you want to know what reviewers think of the book, check out the reviews in Quill & Quire, School Library Journal, and Kirkus Reviews.

And for some cool information about researching the human microbiome - and keeping your research up to date - see Jan Thornhill's Sci/Why post from March of this year.

Truth, the Internet, and the Number of Bacteria on Your Body

by Jan Thornhill

Before I started writing and illustrating kids' books, I did a weekly cartoon for Toronto's Now Magazine. I mined what I thought were entertaining factoids out of whatever I was reading or whoever I was listening to at the time, and illustrated these "truths" in scratchboard. I even called it, for a while, "True Stuff." 

Truth be told, I sometimes accepted as truth anecdotes told to me by other people, or things that came from dodgy sources such as supermarket tabloids. I admit, too, that I sometimes even made up some of what I drew. The above cartoon, however, was supposed to be one of the honest-to-gosh fact-based truths I'd come across and copied into my notebook. Perhaps you've heard or read something similar, something like "bacteria in the human body outnumber the body's own cells by 10:1."

Tasha Sturm, a college microbiology tech, got her young son to gently
press his hand on a petri dish full of agar after he had been outside.
This is the fabulous collection of bacteria that grew! (photo: Tasha Sturm)

When I first came across this "teacupful" tidbit back in 1985, without the luxury of having everything at my internet-connected fingertips like I do today (even in the woods, even in the middle of the night, even a hundred miles from the closest big city), my fact-finding abilities were heavily reliant on what I read in books, newspapers, and magazines. Back then, I had to trust what I read, mostly because it was so very difficult to question the veracity of the printed word. How, back then, if I had questioned the trustworthiness my source, would I have been able to verify if it was true? I mean, even if something like the above statement about "a teacupful" of bacteria was sourced from, say, a research paper in an obscure journal, how would I, a non-academic, have been able to access such a thing back then? 

A close-up of the large flower-shaped colony from the above photo
that is probably made up of several million bacteria (Tasha Sturm)

My point is that back then, in the olden days before the internet, I had an excuse to repeat things that were sometimes untrue. Or at least more of an excuse than I have now. (I also seemed to have a heck of a lot more spare time back then, precisely because I didn't have easy access to so many of the scientific papers I now read—but that's a different story.) 

Back to the number of microbes on and inside a human body. I would never have fished out this old cartoon if I hadn't recently come across the following headline (on the internet, of course!): "Scientists bust myth that our bodies have more bacteria than human cells."

Artist Rogan Brown's amazingly beautiful (and intricate!)
hand-cut paper sculpture of a bacterium  (Rogan Brown)

Here's the gist of what's come to light. This 10:1 bacteria-to-human-cell statistic, which gets almost nine thousand pre-2016 hits on Google, is based on a statement published in a review in 1977, a statement which had, in turn, been based on an earlier unsubstantiated calculation taken from a 1972 article. A group of researchers in Israel and Canada now say the ratio is more likely to be, on average, closer to one-to-one. Some people might have double that number of bacteria, some only half. And everyone loses almost their entire microbial load on a daily basis—at least they do if they're "regular," since the vast majority of human's bacteria reside in the colon. So the ten-to-one ratio is actually an academic urban legend.

But there's the rub: I haven't actually read the new study, nor have I read either the journal article or the review from the 1970s that I've cited in this post. Am I lazy, or is it reasonable for me to trust the distilled versions of the paper that have been published on the websites of the journal Nature, the National Geographic, and Scientific American, among others? I can't answer that. All I know is that it's getting harder and harder to figure out what is believable, not just on the internet, but also in contemporary books since so many are now based on internet research. I just hope I rehashed the gist of what I've been reading about the current research without garbling it too much—because I'm obviously as capable as anyone else of modifying what I've read when I rehash it.

Artist Elin Thomas uses felt and crochet to create petri
dishes packed with "moulds" and "bacteria." (Elin Thomas)

Take that original teacupful of bacteria "fact" I riffed off of all those years ago. Even with the mighty internet I cannot find a specific reference anywhere to "a teacupful" of bacteria on the human body. What I have found, though, are two separate references to the mass of all those trillions of bacteria found in humans equalling that of "a teacup Yorkie" or as being "roughly the same weight as a teacup chihuahua." Perhaps I was guilty way back then of dropping a qualifier in my copying down of this cool little factoid! 

More Academic Urban Legends:

If you think spinach is a rich source of iron, read this entertaining paper: 

Rekdal, Ole Bjørn. Academicurban legends, Social Studies ofScience August 2014 vol. 44 no. 4 638-654

Check out our very own Helaine Becker's UBC article that highlights an academic urban legend about how pearls are formed! And if you happen to meet Helaine, ask her about Mendel's Peas.

More Information:

Directions for making a bacteria handprint in agar are contained in the Comments section of Tasha Sturm's original post on Microbeworld.org (N.B. Once the plates are grown they should NEVER be opened!!!!! The colonies on the plate can represent millions of bacteria that could potentially make someone sick. Mold also contains spores that could be inhaled causing serious problems as well.)

Rogan Brown's website with more dazzling cut-paper microbe art

Rogan discusses his science-based art in a short video

More of Elin Thomas's work on Flickr and on Etsy 

And if you want to know all about microbes and the human body, pre-order Inside Your Insides: A Guide to the Microbes That Call You Home, the latest book written by Sci/Why's own Claire Eamer (illustrated by Marie-Eve Tremblay)!

References

Scientists bust myth that our bodies have more bacteria than human cells on Nature.com

Ron Sender, Shai Fuchs, Ron Milo. Are We Really Vastly Outnumbered? Revisiting the Ratio of Bacterial to Host Cells in Humans. Cell, 2016; 164 (3): 337

You and Your School Library Need These Books

by Helen Mason

I love reading Science books, especially those written for kids. That's because authors have to know a lot about their topic in order to distill the information into interesting and understandable communications that appeal to young readers. In the following titles, Jennifer Gardy and Tanya Lloyd Kyi make challenging scientific information readily available to young readers. These books should be in every elementary school library — and the collections of all teachers who hope to interest students in modern science.

It's Catching: The Infectious World of Germs and Microbes written by Jennifer Gardy and illustrated by Josh Holinaty (Owl Kids, 2014) uses a combination of text, visuals, and anecdotes to introduce readers to the many germs with which we share this planet.

The author, herself a disease detective, introduces past disease detectives, such as Antonie van Leeuwenhoek, the first person to see the microbial world. She explains that microbes exist both in the world around us and in our own bodies. Some of the details provide the necessary gross factor that kids love.

Without boring the reader, Grady outlines the difference between viruses, bacteria, fungi, and parasites. There's also a dangermeter for diseases that range from the common cold and influenza to malaria and ebola.

Discussing why doctors are so worried about parents who don't have their kids vaccinated against measles? Mention the 165 BCE measles plague that killed off about one-third of Rome's population. Have students of Irish descent? Suggest researching family trees to find out how many have ancestors who came to Canada following the 1845 Irish potato blight.

DNA Detective by Tanya Lloyd Kyi and illustrated by Lil Crump (Annick Press, 2015) is equally interesting. The intro draws kids right into the topic by showing a crime scene. Someone broke into a jewellery store and got away with valuable jewels. The perpetrator wore gloves. One was left at the scene. There are no other clues.

Readers will enjoy trying to pick the culprit from a list of suspects who include the store's manager, bookkeeper, custodian, and two cashiers, as well as three customers (two of them identical twin supermodels), a sales rep, a security guard, the owner of the store next door, and a convicted thief. They can follow the thinking processes of a young detective on her first case as she collects DNA evidence in an effort to identify the culprit. 

The author compares DNA identification to a high-tech fingerprint. Both can be inadvertently left behind and collected from crime scenes. The book includes profiles of past DNA rock stars, such as Gregor Mendel and Rosalind Franklin. A cartoon page or spread at the end of each section brings readers back to the crime in question. The detective outlines what she's learned. In most cases, readers can use this information to eliminate suspects. By the end, the detective — and readers — have their man — er, woman.

Books such as these provide excellent introductions to topics kids will continue to learn about throughout their student years — and likely their entire lives.