Today we’re talking about tiny microbes, usually so small that a microscope is required for any chance of seeing them. But it’s possible to see some microbes without a microscope. Actually, it’s even possible to see them at a great distance. I’m not talking a few feet, I’m talking miles. It’s possible to see microbes from space. Yes, you read that correctly. SPAAAAAAAAAAAACE.
I admit, this seems a little far-fetched. After all, we’re talking about organisms that are called “microscopic” for a reason. Where are these microbes? You can see them where we always find the world’s most interesting organisms…
The oceans are full of life. Viruses are the most abundant organisms in the oceans (if you count viruses as organisms), but other microorganisms make up most of the biomass. Amongst the sheer biomass of microbes in the oceans, the whales and sharks are almost non-existent. Living terrestrially is tough, but that doesn’t mean life in the oceans is a breeze. Marine microbes have evolved countless adaptations to help them survive in a marine environment. Most of the oceans are relatively cold. This poses a problem for our tiny ocean friends because it directly affects their metabolism and growth. Even worse, cold temperatures affect their membrane “fluidity” and cytoplasm/water viscosity, which in turn restricts their swimming/movement. Many have evolved alternation in their fatty acid composition and modified enzymes that are more efficient at lower temperatures.
As most people are aware, the oceans are also salty. This causes a strong osmotic effect, it can impair enzymes, and alter how proteins fold. But microbes even manage to work around those problems. Adaptations include specialised cell walls, improved salt tolerance, and some species have actually evolved to require the high salt levels! There are many other problems. They have to avoid drying out and sinking, they have to protect themselves from intense UV on the water surface due to reflection, and they have to survive in a low-nutrient environment. It’s a tough life.
This is Rhizosolenia, a diatom. Notice the scale? That little scale bar represents 0.005 cm. Rhizosolenia has to deal with all the problems I’ve already mentioned, from low temperatures to low-nutrient supply. Their best solution is location, location, location. This next image shows where Rhizosolenia live in the Pacific ocean.
A northward current is coming in from the left, and a southward current is coming in from the right. When they meet, the cooler water from the south moves deeper into the ocean, which stirs up the warmer waters. Between them, a front is created by convergence of the water masses of different temperature and density. The southward current is nice and warm, and the northward current brings delicious nutrients. The Rhizosolenia live on the warmer side of the front, using the nutrients that come from the colder waters. Rhizosolenia thrives here, and can be found wherever this front occurs in the Pacific. You can see them if you look closely at the next image.
Now that’s a lot of Rhizosolenia! No microscope required there. But that photograph was taken from a boat. Here’s something a bit more spectacular…
That line you can see is Rhizosolenia. Each individual is only a few micrometers across, yet that line is approximately 57 km long. You’re looking at microbes, as seen from the space shuttle Atlantis. Here’s my favourite image…
The line of Rhizosolenia running through the centre of this image is 100 km long. This photo was taken 230 km above the Earth’s surface. Carl Sagan spoke of gazing upon our lonely blue planet from deep in the solar system and being unable to see any evidence of humans.
“And yet there is no sign of humans in this picture, not our reworking of the Earth’s surface, not our machines, not ourselves. We are too small.”
It seems just as likely that microbes would be invisible to observers hundreds of kilometres above the Earth’s surface. But there they are, photographed by the astronauts of the space shuttle Atlantis on the 7th of August, 1992. Recently, Atlantis was retired safely, but you may have noticed on the news that yesterday marked the 10th anniversary of the space shuttle Columbia disintegrating during re-entry. I’d like to take a moment to remember the explorers that lost their lives. They will always be remembered. Once again, I leave you with Carl Sagan.
“To live in the hearts we leave behind is to never die.”
Yoder, J.A., Ackleson, S.G., Barber, R.T., Flament, P. and Balch, W.M. (1994). A Line in the Sea, Nature, 371, pp. 689-692.