11/17/2004
Relating to a Sponge Named Bob
Kudos to our granddaughter, Dale. Her solo piano recital on Sunday was no less brilliant and stirred the emotions no less than the two performances by Lang Lang and Yefim Bronfman that I mentioned in recent columns. As a self-appointed music critic, I feel I can offer these opinions without a grandfatherly bias. Not only was her performance great but the next day she passed her driver’s test on her 17th birthday. But I must not ignore her brother, Doug, our 11-year old grandson, who first introduced me to a sponge named Bob last summer. I watched this fellow on TV for a few minutes and thought how ridiculous to make a cartoon character out of a sponge.
Now I find that Bob is featured in a movie appropriately titled “The SpongeBob Squarepants Movie”. For those of you who are unfamiliar with this unlikely cartoon character, SpongeBob is a rectangular-shaped sponge of the size and shape of the kitchen sponges we buy at Trader Joe’s. Unlike our sponges, this character has a face and arms and legs and is so popular that there was a feature on SpongeBob on the Sunday Morning TV show this week. If I remember correctly, it was stated that the SpongeBob TV program draws some 57 million viewers, about a third of them adults!
After watching Sunday Morning, I was still puzzled that both children and adults could relate to a sponge. Then I came across an article, “This is Your Ancestor”, by Jack McClintock in the November issue of Discover magazine and realized that we all should feel close to Bob. The article discusses the work of Mitchell Sogin, an evolutionary biologist at the Marine Biology Laboratory in Woods Hole, Massachusetts. Last week we discussed evolution and hobbit-sized humans living alongside us modern humans as recently as 12 to 18 thousand years ago.
Sogin’s interests extend much more distantly in our past. Two decades ago, he set out to answer the question, “What was the first animal?” We’ve discussed before how single-cell bacteria and such organisms formed billions of years ago and how it was much later that more complex life evolved. You’ve probably guessed, if you didn’t know already, that Sogin’s work has led to a completely unexpected conclusion – the first animal was SpongeBob! OK, we should call that animal SpongeAdam and it certainly wasn’t the rectangular Trader Joe’s sponge, which I suspect might be a synthetic product.
It’s tempting to think of the sponge as a plant, as I did when I first stumbled across a sponge washed up on a beach. Indeed, biologists early on did classify it as a plant. After all, except for Bob, it doesn’t have arms or legs, organs, tissues or a brain. One feature of most plants, and the sponge, is that they tend to anchor themselves in place and don’t move around. However, in 1986, biologist Calhoun Bond at the University of North Carolina used time-lapse photography and filmed some sponges in glass tanks. Both saltwater and freshwater sponges actually did move around, even going so far as to climb up the walls of their tanks. One of the speedier sponges traveled at all of four millimeters (less than inch) a day!
Sponges come in thousands of varieties and range in size from a fraction of an inch to as large as 8 feet tall and are flourish in both hot tropical and cold Arctic waters. Unlike Bob, real sponges exhibit a range of much more loosely structured forms resembling bushy cauliflowers, cups, fans tubes, piecrusts, etc. The sponge eats by filtering the water surrounding it through a multitude of tiny pores into a central chamber; the water exiting through an opening called the osculum. An ocean-dwelling sponge may have to filter a ton of seawater to obtain just an ounce of food. Most sponges are hermaphrodites, spewing out both sperm and egg cells.
How did Sogin arrive at the conclusion that the sponge was the first animal to arrive on the scene about half a billion years ago? We’ve talked in past columns about DNA and its coding in chains of four compounds abbreviated by the “letters” C, G, A and T. We’ve also talked about genes, sequences of the DNA that code for producing proteins, and how our complete set of DNA is currently thought to contain roughly 20,000 genes. When Sogin started on his quest this work 20 years ago, to sequence a single gene was a major task.
What Sogin did was to pick one particular sequence for a gene that had a specific function common to all animals. He picked a gene that is used by cells to make a certain protein. Sogin’s gene sequence has about 2,000 of the C, G, A and T “letters” (the complete human genome has 3 billion). What Sogin did was to determine the sequences for this gene in different organisms, looking for differences in the sequences that would show how the gene, and the corresponding organism had evolved away from another organism. He started by looking at various kinds of marine organisms, including sponges, algae, jellyfish, etc. You have to admire this guy’s perseverance. It took him a year just to sequence one gene from a red sponge, the most common sponge!
Fortunately, as gene technology advanced, Sogin’s output increased and soon he was producing 10 to 15 gene sequences a year. To show how far genetic sequencing has progressed, with today’s automated sequencing he can sequence a thousand genes overnight! By comparing his selected gene in marine animals with the same gene in insects, birds, worms, fish and mammals, Sogin came up with an evolutionary tree. This tree led him back to the sponge as the first animal. The sponge’s blueprint would serve as the jumping off place for the other animals to follow. No wonder we feel a kinship with SpongeBob.
But Sogin didn’t stop there. What came before the sponge? There were the “choanoflagellates”. These were single-celled organisms characterized by having a tiny filament called a flagellum and a collar of teensy hairs known as microvilli. They were close to being animals but not quite. Well, sponges contain only a few types of cells, one being a “choanocyte” (note the name’s similarity to choanoflagellate). Sure enough, the choanocyte cell has a flagellum and a collar of microvilli.
In a sponge, there’s another type of cell, the “archaeocyte”, which can change its shape and its function when necessary to absorb food, make new skin or reproduce. It seems a good bet that this cell and a flagellate-type cell got together and decided it was to their mutual benefit to hang out together in the form of a sponge. But Sogin wasn’t finished yet. We’ve got even older “relatives” – fungi! His gene sequencing has shown that fungi are quite different from plants and actually are more closely related to animals. He says that this doesn’t mean that we humans are just highly evolved mushrooms but rather that we share with fungi a common group of ancestors that split off into separate groups which would become fungi and animals.
This finding may not seem relevant to our everyday life today, but wait. There’s another cartoon character you may have seen on TV commercials and it’s not as appealing as SpongeBob. I’m referring to that little critter that pries up your toenail and sets up shop underneath it with his fungi cohorts in a thriving fungal community. (I admit to having just such a colony under my own big toes – yuck!) This type of infection, and similar fungal annoyances such as athlete’s foot, don’t represent life- threatening situations. However, other fungal infections such as endocarditis, an inflammation of the heart muscle (caused by either a fungus or a bacteria), can be more serious. There’s also an organism that has killed thousands of HIV patients. Sogin and coworkers have shown that organism to be related to a fungus, not to malaria as previously thought.
Why do these fungal organisms have such an easy time infecting us? Sogin and colleagues say that it’s because we and the fungi are so much alike, sharing the same family tree in the far distant past. Accordingly, our immune systems find it difficult to see a fungus as an intruder. The treatments used to combat these infections should be ones that target fungi and to come up with such treatments we would do well to cultivate more fungi in the lab and test our drugs against them.
Finally, a grammatical note. I started this column with the word “kudos”. I looked up the word in my dictionary and was shocked to find that “kudos” is not the plural of a word “kudo”. Dale, you deserve more than one kudos.
Allen F. Bortrum
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