When times get tough, bacillus gets pregnant. Normally the common soil bacterium divides by binary fission; it doubles its chromosomes and builds a septum--a wall--right down its center, dividing itself in half and producing two identical twin cells. But when food starts to run out, and survival becomes paramount, such equality is the first thing to go. Binary fission is still the order of the day, but the precursor cell now places the septum closer to one pole than another, producing two unequal cells-- only one of which will survive.
The larger of these cells, now called the mother cell, engulfs its smaller sibling, now called the forespore, creating a cell within a cell. For some ten hours, the mother nurtures that forespore, using most of its energy to stitch together a sturdy protein coat for the life growing within. Once completed, this coat will help make the spore one of the hardiest creatures on the planet.
There’s probably no other life-form that is more tolerant of environmental extremes than the spores of Bacillus and related bacteria, says molecular biologist Richard Losick of Harvard. The center of it is almost like a freeze-dried environment in which water is removed and the DNA and the ribosomes and so forth are all in a semicrystalline state. They can survive for very long periods of time--many years, probably at least hundreds of years. (Other researchers think the bacteria can survive far longer than that: in May a team from the California Polytechnic University in San Luis Obispo described finding and reviving spores of Bacillus sphaericus from the abdomen of a bee trapped in amber. The spores, says microbiologist Raúl Cano, were 25 million years old.) But for the mother, time is fleeting. Once the coat is completed, the mother cell will lyse-- its membrane will disintegrate or burst open, the contents of the cell will spill out, and the spore will be set free to find greener pastures. It’s the ultimate act of maternal sacrifice.
Sacrifice and altruism are concepts not commonly associated with bacteria; nor are bacteria known for going so willingly to their death. Bacteria, in principle, are immortal cells, dividing unchecked until dispatched with a good dose of antibiotic or a stiff swab of antiseptic. But researchers are now discovering that everywhere you look in the bacterial world, rather than immortal life, you find death.
