Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [27]
Four
THE E. COLI WATCHER’S FIELD GUIDE
A HUMAN KRAKATAU
ON AUGUST 26, 1883, a little world was born. An island volcano called Krakatau, located between Java and Sumatra in the Sunda Strait, hurled a column of ash twenty miles into the air. Rock turned to vapor and roared across the strait at 300 miles an hour. The eruption left a submerged pit where the cone of the volcano had been, along with a few lifeless islands. Nine months later, a naturalist who visited the scene reported that the only living thing he could find was a single small spider.
The new islands of Krakatau lay twenty-seven miles from the nearest land. It took years for life to make its way across the water and take hold again. A film of blue-green algae grew over the ash. Ferns and mosses sprouted. By the 1890s a savanna had emerged. Along with the spiders came beetles, butterflies, and even a monitor lizard. Some of the arriving species swam to the islands, some flew, and some simply drifted on the wind.
These species did not take hold on Krakatau in a random scramble. Rugged pioneers came first and later gave way to other species. The savanna surrendered to forests. Coconut and fig trees grew. Orchids, fig wasps, and other delicate species could now move onto the islands. Early settlers such as zebra doves could no longer find a place in the food web and vanished. Even now, more than 120 years after the eruption, Krakatau is not finished with its transformation. In the future it may be ready to receive bamboo, which will revolutionize its ecosystem yet again.
The history of Krakatau followed ecological rules that guide life wherever new habitats appear. Volcanic eruptions wipe islands clean. Landslides clear mountainsides. As glaciers melt, shorelines bounce out of the sea.
And babies are born. To microbes, a newborn child is a Krakatau ready to be colonized. Its body starts out almost completely germ free, and in its first few days E. coli and other species of bacteria infect it. They establish a new ecosystem, which will mature and survive within the child through its entire life. And it will develop over time according to its own ecological rules.
There is much more to E. coli’s life than can be seen in a petri dish. Its pampered existence in the laboratory makes very few demands on it. Out of the 4,288 genes scientists have identified in E. coli K-12, only 303 appear to be essential for its growth in a laboratory. That does not mean the other 3,985 genes are all useless. Many help E. coli survive in the crowded ecosystem of the human gut, where a thousand species of microbes compete for food.
A scientist studying E. coli in a flask may completely overlook some of its essential strategies for surviving in the real world. For all the work that has gone into E. coli over the past century, for example, microbiologists often fail to acknowledge just how social a creature it is. To survive, E. coli work together. The bacteria communicate and cooperate. Billions of them join together to build microbial cities. They wage wars together against their enemies.
In the real world there is no single way of being an E. coli. E. coli K-12 is just one of many strains that live in warm-blooded animals and have many strategies for surviving. Some are harmless gut grazers. Others shield us from infections. And still others kill millions of people a year. To know E. coli by K-12 alone is a bit like knowing the family Canidae from a Pomeranian dozing on a silk pillow. Outside there are dingoes and bat-eared foxes, red wolves and black-backed jackals.
FINDING A HOME
E. coli is a pioneer. Long before most other microbes have moved into a human host, it has established a healthy colony. E. coli may infect a baby during the messy business of childbirth, hitch along on the fingertips of a doctor, or make its leap as mother nurses child. It rides waves of peristalsis into the stomach,