How to see microbes from space

Microbes are tiny. Usually you need a microscope in order to see them, hence the name. With the right conditions, however, it’s possible to see tiny microbes without a microscope and from a great distance. I’m not talking about centimetres or yards; I’m talking miles. Believe it or not, it’s possible to see microbes from space. Yes you read that correctly. Space. You have to look for them in a very specific place though, so first let’s talk about living in the ocean.

Our oceans are full of life. Viruses are the most abundant organisms in the oceans (if you count viruses as living things), but other micro-organisms such as bacteria make up most of the biomass. Living on land 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. For example, 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 microbes have evolved alternation in their fatty acid composition and have modified enzymes that are more efficient at lower temperatures.

As well as cold temperatures, microbes have to deal with the fact that our oceans are salty. This causes a strong osmotic effect, which can impair enzymes and alter how proteins fold. Adaptations include specialised cell walls and improved salt tolerance. Some species have actually evolved to require the high salt levels! There are many other difficulties beyond cold temperatures and salty water: microbes 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 schematic shows where Rhizosolenia live in the Pacific ocean. The water surface is at the top of the image. 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. The individual cells are microscopic, but they are found in such high numbers at this front that you can clearly see them from a boat with your naked eyes.

Now that’s a lot of Rhizosolenia! No microscope required there. Let’s zoom out a bit further.

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.

This is among my favourite space photographs ever. 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. In Pale Blue Dot, Carl Sagan spoke of gazing upon our lonely 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.”

If we’re too small, you could be forgiven for thinking that tiny 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.