Said the MIT professor Sallie Chisholm as she spoke to an audience of alumni at MIT’s Technology Day last Saturday. She was not talking about a nanotech infestation that was turning the seas into computronium. Well, actually, she was. It was natural nanotech, the bacterium Prochlorococcus, the smallest and most abundant photosynthetic organism known. There are 100,000 of them in a milliliter of seawater, and maybe 10^27 of them on earth. They have generated about 20% of the oxygen in the atmosphere. They live in the top 200m of the ocean, the sunlit zone, and are found from the poles to the equator.
They appear to be a vast super-organism. There is huge genetic diversity among the individual cells. There are only 2000 genes in all its DNA, but 800 of them vary from cell to cell. The variations allow them to adapt to different levels to sunlight, and of temperature, and of nutrient availability. The variations are transmitted from cell to cell by viruses. There are millions of these viruses per milliliter of seawater, and they float from cell to cell like chemical nerve impulses.
They’re the bottom of the food chain. Zooplankton eat them, and krill eat the zooplankton, and whales and Japanese and everything else eat the krill. They’re a kind of blue-green algae and have been here for billions of years.
Yet here’s the thing – they were only discovered in 1985. They’re so small that they went right through the filters before that. Prof. Chisholm was one of their discoverers, actually, due to a new flow cytometry technique she had developed, a means of counting cells in a stream of water. People had seen the chlorophyll in them before that, but thought it was due to the breaking open of larger cells. They also weren’t seen in cultures because they don’t happen to like to grow in Petri dishes.
And it’s only been in the last five years that they’ve been able to measure their genetic diversity. There are instruments now that can sequence the DNA in individual cells. They’ve done 11 strains so far, and 3 of the viruses that infect them.
So this major component of the Earth’s ecosystem wasn’t even known until recently, and is only now coming to be studied. There are now stations off Bermuda and Hawaii measuring their population. “Visiting them is one of the benefits of being in this field,” said Chisholm, but then added “although the stations are there because the prochlorococcus like warm water.” Uh-huh. Better there than the McMurdo or the Barrow stations.
“All nice and interesting,” you might think, “but how can money be made off of them?” Through a scheme called iron fertilization. This is a means of reducing global warming by causing blooms of phytoplankton with iron particles. Iron is a key nutrient for these creatures, and is unavailable in a lot of the ocean. Proponents estimate that one tonne of iron can prompt enough phytoplankton growth to suck out 80,000 tonnes of CO2. It could be a profitable venture if it’s used to get carbon capture credits from the Europeans.
Yet Chisholm knows how little she knows about all this, and so is a skeptic. She notes that if the plankton sink down and get eaten by something else, they could create anoxic zones in the deep sea. The death and decay of those predators could release methane and nitrogen oxides, which are much worse greenhouse gases than CO2. “Today’s solutions are tomorrow’s problems,” she says. “If you want less CO2, don’t produce it in the first place.”
Her talk at MIT isn’t yet available on their video site, but there’s an earlier one here: The Invisible Forest – Microbes in the Sea. She’s a funny, if gawky, speaker. She thinks microbes in general have gotten a bad rap because of disease, and as proof brought a collection of plush toy microbes from giantmicrobes.com. “Look at this – ebola, rhinovirus, and the flu! Where are the good microbes that live inside us?” So one of her grad students modified a round green one to be Prochlorococcus. Here’s the tiny little bio-machine on which we all depend. Wouldn’t it be nice to know how they worked?