A sea microbe humbles scientists and inspires reverence


Earth and Spirit

Meet the oceans’ Prochlorococcus -- the most important microbe you’ve never heard of. It’s given us a new understanding of how the Earth works creatively and cooperatively.

It’s one of the microorganisms that inhabit the well-lit upper waters of the planet’s seas and emit gas or gaseous compounds. One algae, Emiliana huxleyi, for example, emits dimethyl sulfide, which contributes to what we call the smell of the sea.

An unseen zoo of these microscopic beings fills the upper levels of oceans, exerting an influence on this planet every bit as profound as the land’s forests. The diverse phytoplankton species inhabiting the ocean’s surface waters -- which mainly consist of single-celled cyanobacteria, diatoms and other kinds of algae -- form the base of the marine food chain.

They account for roughly half the photosynthesis on the Earth, remove nearly as much carbon dioxide from the atmosphere as all plants, and supply about three-quarters of the oxygen we breathe.

A new one was just discovered in 1986 -- a blue-green algae not known to exist until its discovery. It was given the name Prochlorococcus (pro-cloe-row-cock-us). It’s perhaps the most abundant living creature on the globe. These minute creatures employ chlorophyll to produce as much as one-fifth of the world’s oxygen. Every fifth breath you take, thank Prochlorococcus.

A young researcher at the Massachusetts Institute of Technology, Sallie Chisholm, first found the creature in the Atlantic, on a research vessel traveling to Bermuda. They were using a device known as a flow cytometer to pick up samples of a particular blue-green algae they knew existed.

What they did not foresee was that the device would show the existence of millions and millions of even tinier creatures -- oval-shaped entities, around 6 microns in diameter, one two-hundredth of the width of a human hair. Examined under an electron microscope, they were found to have built into their workings a type of chlorophyll that permitted them to absorb carbon dioxide to extract from seawater a tiny amount of oxygen which then escapes into the atmosphere.

Taken one by one, the amount of oxygen that any one of these algae produce is insignificant; but Chisholm calculated that Prochlorococcus existed in such large numbers -- 100,000 of them in a single cubic centimeter of water, perhaps a trillion trillion of them in all -- that they were quite probably the most common creature in all the world, and would in total produce large quantities of oxygen.

They live in warm seas, essentially wafting around between 40 degrees north and 40 degrees south. At the bottom of the food chain, they drift waiting to be eaten by tiny shrimp that would then be gobbled by small fish, and on up to humankind’s seafood restaurants.

Chisholm felt that Prochlorococcus was an example of how once again nature had displayed its infinite capacity to humble the world of science, and could readily do so again. Before 1986 we didn’t know it existed; now it is recognized as perhaps the most common being on Earth and it plays a central role in keeping land-based creatures alive.

If anything disastrous happens to it, the survival of all beings that require oxygen would be placed at serious risk. In the 25 years since its discovery, a lot of research has been done on what might harm it, and how. Researchers have been trying to find out whether the warming of the seas due to global climate change might limit its ability to absorb carbon dioxide and foreclose on its ability to produce oxygen.

Prochlorococcus seems to be resilient to the warming, liking warm seas and flourishing in them. Any increase of sea temperature might cause its range to expand beyond the present 40-degree lines, and that might have its own effect on the absorption of carbon dioxide.

“It is tempting -- but entirely fanciful -- to imagine that such a development might balance some of the expanded emissions of greenhouse gasses that are so troubling humankind today,” writes oceanographer Simon Winchester.

An expansion of the range and population of Prochlorococcus would demonstrate a component of Earth’s self-regulating mechanism, so crucial to James Lovelock’s famous Gaia hyphothesis -- which holds that the world is to be viewed as a self-contained living being, able to change its own ways and to deal with its changing circumstances.

“Prochlorococcus is very special,” says Chisholm, “because it’s filled with superlatives. It’s the smallest photosynthetic cell in the world as far as we know and it has the smallest genome of any photosynthetic cells so, with the smallest number of genes, it can convert solar energy, carbon dioxide and inorganic compounds into organic carbon.

“I think of it as the minimal life form. It doesn’t rely on other organisms for organic carbon, it creates everything de novo and also, it turns out it’s the most efficient light absorber of all known photosynthetic cells, and we think it’s also the most efficient carbon fixer of these cells.”

Oceanographers think that this system is playing an important role in regulating the stability of the ocean ecosystem, and yet they have no idea how to articulate that in any mechanistic way. “They’re essentially like dissolved photosynthesis machines in the oceans and I think of the information in their DNA as dissolved information,” says Chisholm. “The oceans are loaded with this genetic code instructing cells to go through photosynthesis and take up nutrients and do all of these living processes in the ocean.”

Again, the Gaia hypothesis comes to mind, offsetting in a big way the popular notion of competition and survival of the fittest as nature’s prime way. Can we take this cooperative model as a blueprint for an ethic of Earth-healing? We’re pragmatic people, but we seem incapable of making the connection between what we are doing to the Earth on a daily basis and the increasingly uncertain future of humanity.

Indeed, British astrophysicist Martin Rees, who won the Templeton Prize in Science and Religion this month, wrote a book recently, Our Final Hour, in which he gives humankind only a 50-50 chance of surviving until 2100.

Can this new understanding of Gaia, of Earth, lead to a more compassionate, respectful, holistic way of living? As Catholic theologian Elizabeth Johnson points out: “Every fresh morning, every star of night, speaks of the Creator Spirit who pervades the world with creative power, giving rise to all manner of systems and species.”

We’re still uncovering the mysteries of that handiwork -- like this star of the sea, Prochlorococcus.

[NCR staff writer Rich Heffern is editor of the Eco Catholic blog at NCRonline.org/blogs/eco-catholic. His e-mail address is rheffern@ncronline.org.]

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