I help water to freeze and ice to fall, and can make clouds rain at my command.

Birds have large wings and streamlined bodies to help them stay aloft. But if you’re small enough, you don’t need to be a special shape to fly. The air will lift you up anyway.

Even if you don’t want to be lifted.

Don’t get me wrong. A nice, good wind is useful, if you want to get from one place to another. Down in the ocean, or on the leaf of a plant, your body can only move itself around so far. But if you want your species to spread — if you want to go explore, discover, travel, colonise the world — then air is the way to go.

It’s all a matter of luck, of course. You have to wait for the spray of a wave to ride upon — or, if fortune is on your side, a stronger wind, hurricane or cyclone. Land-dwellers have it easy: there’s usually an updraught of rising air going from the warm ground to the cooler sky, not to mention water evaporating from the plants. All there is to do is hop on.

The land is also where lots of things happen. Animals stamp the ground in a moving herd, throwing up dust — and you — into the sky. Birds fly up and down, ferries waiting for a passenger. Sometimes a human-run airplane will carry you right into the stratosphere. And you can always hitch a ride on the spore of a rust-fungus, or anything else which is better at drifting than you are.

None of those creatures know they’re helping us, of course. They’re just going about their own business. Most aren’t even aware we exist, let alone that they’re doing something for us. The average human, for instance, thinks of me as a pest that causes frostbite for his plants — and that’s if he even thinks of me at all.

Plants, you see, are a great food source, if you know how to get in. And I do know how: by making them freeze. When the water in plants turns into solid ice, it disrupts and damages the plant tissues — making an easy entrance for folks like me to enter.

Of course, humans don’t like me damaging the plant to take nutrients. They’d prefer they did it themselves.

Earlier, humans used to be a bit more aware of the people around them. They used to have special events like the ‘rain dance’, conducted to help bring down the rain.

Now, I suppose you’re wondering how on earth dancing can have anything to do with helping to make rain.The answer is really quite simple. Rain-dances are supposed to help please the rain spirits. That’s me: the Pseudomonas syringae.

I am the master of water. I dwell anywhere from lakes and oceans to cold, frozen glaciers. I help water to freeze and ice to fall, and can make clouds rain at my command.

Clouds are very comfortable things to travel in, at least for a while. With the wind behind them and all the water you can ever want, a cloud you can live in forever is like a castle in the air. But clouds don’t have all the food and nutrients found down below, so you’ll have to return eventually. Luckily, disembarking from a cloud is something I’m good at. Not like trying to get down from the stratosphere.

If you remember the beginning of our little conversation, I said something about wind lifting you up even if you don’t want to be lifted. Well, that’s kind of what happened to me.

It started off in the usual way, with one of those underwater chases. A flying-fish leapt out to escape from an oncoming predator, carrying me with the spray. This was fine by me, as the area had been getting a bit understocked, so to speak, and a change of scene was quite welcome.

Now, you have to understand that air-travel is a chancy business. Above a planted field you can move six metres a day just by drifting around, and some fellows will always manage to keep going higher. The others, though, they’ll come right back down. That’s how the probability works.

You’ve got to just drift around, hoping you catch a good updraught.

Well, I guess you can piggyback on something else. The spores of rust-fungi, for instance, are very good drifters. It’s their business to get as high up as possible; it’s what they’re designed for.

Me, I prefer staying alone and letting the wind take me where it will. My area was nice enough, in a way, and I didn’t see the point of moving more than a few kilometres.

This time, however, the wind seemed determined to take me further. I must’ve gotten caught in the eye of a storm, for before I knew it, I was higher up than I’d ever been before. The air was much thinner here, and much colder. And it was dry. So dry, it was all I could do to keep my own body-water from going back out. Something told me I was moving sideways at an incredible speed, and that was when it hit me: I’d reached the stratosphere.

Every time a hurricane blows, billions of microbes get thrown up into the sky. Most return soon after the winds calm down. Others get onto the continent-crossing Trade Winds, or voyage through one of the many other highways in the sky.

And then, there are the poor creatures who keep drifting helplessly up till the stratosphere — a dry cold place, high above where weather happens, and hard for anyone to survive in. Many don’t survive.

Still, we’re better off than large animals and birds designed to spend their whole lives near sea-level. Even if they could tolerate the freezing cold, survive the dry air and low pressure without bursting their lungs and having their blood boil out — even then, they’d still have to contend with cancer-causing ultraviolet radiation from the Sun.

You see, the stratosphere houses the Ozone Layer: a planet-covering shield of ozone gas that blocks the worst of the Sun’s rays.

You might remember the Ozone Layer from the time when humans accidentally began to destroy it. There was excitement at that time because people thought we were going back to the old days of radiated soil ruled by UV-resistant bacteria. Unfortunately, though, the humans soon caught on and stopped their activities.

Incidentally, what they were trying to do was similar to my speciality: helping things freeze.

You see, water doesn’t always freeze on its own. Sometimes, even if it’s cold enough, it needs a little boost to get started. Water freezes by aligning its atoms into a certain fixed pattern, but unless it’s really super-cold, it needs a small bit of already-complete pattern to copy from. And someone who can make that pattern is me. Or rather, a special protein in my cell-membrane that arranges water in the correct way. This protein is what makes me — along with other bacteria — into an ‘ice nucleating agent’.

Why “nucleating”? A nucleus is the something right in the centre. And when the first ice freezes, that something right in the centre is me.

But I digress. As I was saying, this ozone place is one of the layers in the stratosphere. And when you get above it, there’s nothing protecting you from the Sun’s radiation. It’s fortunate that we bacteria have some immunity — an immunity that goes back to before the Ozone Layer even existed.

3.2 billion years ago, the world was very different. This was long before the Biological Revolution gave us the numerous animals and plants of today. There was no fur to ride on, no intestines to hide in; no leaves to infect or seeds on which to hitch a ride through the air. Not a single animal walked on this planet — and even if it had, it would have died instantly, because there was no oxygen for it to breathe. All of it was trapped inside rocks, or in the huge amounts of carbon dioxide that made up the early atmosphere.

And there was no ozone either. Ozone, you see, is just a plus-size edition of oxygen. One molecule of oxygen-gas is made of two oxygen-atoms; ozone, on the other hand, takes three. But it still needs oxygen-atoms, and, as I said, there weren’t many of those around.

With nothing to stop it, UV — ultraviolet — radiation bore down on the land, tens of thousands of times as strongly as it does today. So it’s a good thing our ancestors weren’t on land: they were in the water, which served to block off at least some of the rays.

But this was the time bacteria were trying to come out onto land. The oceans were filling up, and there was no reason to leave out the vast inviting spaces up above it. The ‘Terrabacteria’ began to slowly colonise the land — and their slowness gave them strength to experience UV radiation; to adapt and learn how to handle it. Many died, but those that survived emerged all the stronger.

Later, the cyanobacteria came out and began polluting the air with poisonous oxygen. That’s a whole different story, but some of this oxygen eventually went to form the shielding Ozone Layer.

It was another long while before my own genus — the Pseudomonas — evolved. Still, my ancestors came over 500 million years ago, long before plants had even thought of creeping onto land. So as you can see, we’re much more than the plant pests that humans make us out to be.

We are creatures of the water; in water you can find us almost anywhere. We live in the salty ocean, as well as freshwater lakes and ponds. What about a cold frozen snowpack, or a crack in the Arctic ice? You’ll find us there as well, lying dormant till the world turns nice enough for us to come out. We’re there in the moist clouds sailing through the sky — and when cloud turns to rain, you’ll find us in the falling raindrops too.

Myself, I came from a biofilm — a tight community of many different bacterial species, living together under a protective coating. Not all my people live like this, but when we do, it’s nice and cosy.

But I’m the ice-freezing type. More than other strains of my family, it’s what I do. When winter came, things were getting a bit lean, so to speak. I was beginning to feel hungry, but there was nothing to eat. To make matters more annoying, my neighbours seemed to have filled themselves up without telling me about it.

Well, anyone in my position would give them a cold look. Myself, I went beyond looks, which is to say, I made them actually cold. In other words, I froze them. I nudged the cold water around me to turn into ice. That damaged my neighbours’ cells, allowing me to tuck in.

At least, that was the plan.

In my defence, I never knew the ice would spread so fast, turning into solid and wrecking the whole biofilm. So I guess it was my fault, that living conditions when I took to the sky were not quite up to scratch. Even so, I think it’s mighty unfair that I had to spend two whole weeks up in that horrible stratosphere. That’s the maximum length of time a person like me can survive, and it was only luck that nudged me out just in time to meet a passing cloud.

Of course, I didn’t waste time. I made the water vapour freeze up into an ice-ball around me; an ice-ball that melted to a raindrop by the time it hit the earth. Now that humans are less obsessed with seeing me as a plant-parasite, they’re beginning to see how this works.

Clouds don’t just rain, you see. They need something to trigger them. There’s all this moisture in the air, but it needs to condense — get together in one place — to form raindrops. Minerals and salt-particles can help here — they pick up some droplets, and the others decide to join in — but we ice-nucleators are better at it, because we can actually bring the moisture together into ice. And, with our special proteins, we can do it at higher temperatures.

This is also why rain-dances work: they send microbes and dust-particles into the air, making more things for water to condense around. Of course, when those things include us, the effect is very much better.

Strange thing is, humans were so obsessed with plant-parasites, they never realised why rain-dances worked till recently. Older humans did know they were helping us rain-spirits, but they didn’t realise how exactly that help worked, by sending us into the air to find new places to travel to.

Which reminds me, here I am in a new place and haven’t get got round to exploring. It’s been nice talking, but I see some promising crops planted here, which need just a little freezing before I can access their foodstock.

So, please excuse me, while I dig in.

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