Bacteria get old, too

<body leftmargin="0" bgcolor="#000060" text="#FFFFFF" link="#FFFF00" vlink="#FF9900"> <b> <p class="MsoNormal"><font face="Arial" size="4">Bacteria get old, too</font></p> </b> <p class="MsoNormal"><font face="Arial" size="1">Posted Feb. 16, 2005<br> Special to World Science</font> </p> <b> <p><font face="Arial" size="2">Scientists have always assumed the simplest bacteria never get old. How could they? They just eternally multiply by splitting in two, so there’s no clear way to tell how “old” one is. Their apparent agelessness raised hopes that we could one day return to that happy state. <br> <br> No such luck, a new study has found. <br> <br> Researchers have found that one of the simplest bacteria, Escherichia coli, get old. This raises for the first time the possibility that there is no such thing as an immortal creature, the researchers said. It also forces scientists to rethink how aging occurs—and how to get rid of it.<br> <br> The researchers basically found that each bacterial cell contains a “new half” and an “old half.” Cells containing very old halves become the bacterial equivalent of feeble old men. The findings come from researchers at the National Institute of Health and Medical Research in Paris, France.<br> <br> The finding is “remarkable” because it overturns some basic scientific assumptions about aging, wrote Thomas Kirkwood of the University of Newcastle, Newcastle Upon Tyne, U.K., a prominent theorist on aging, who wasn’t one of the researchers that made the new finding.<br> <br> Some of these assumptions were used to develop what today are the most well-accepted theories of why aging occurs. <br> <br> These are called evolutionary theories because they stem from the theory of evolution, which holds that all living creatures descend from those past ones who were best able to survive and breed. They pushed aside the less successful ones. In each generation, some creatures randomly acquire mutations, a tiny fraction of which are “good” mutations that help them survive or breed better in some way. When these creatures spread, the mutations spread too, so the best mutations establish themselves in populations.<br> <br> Some of the most popular theories of aging claims that aging occurs because some mutations help early in life but hurt later on. For instance, a mutation might help bones grow faster early on, but lead to arthritis from excessive bone growth later. Evolution lets these mutations become established despite their harmfulness, because in the wild, most animals get killed before the harmful effects become apparent. <br> <br> Some scientists have called these ideas “pay later” theories.<br> <br> The belief that some creatures were immortal was an important factor in “pay later” theories, especially some versions of it.<br> <br> Kirkwood, for instance, developed a theory that has been considered a variety of “pay later.” But instead of distinguishing between “early” and “late” in life, Kirkwood distinguished between two kinds of cells: the reproductive cells, such as sperm and eggs, and the rest—which are our bodies.<br> <br> Evolution would work to hardest to preserve and perpetuate the reproductive cells, even at the expense of the others. Anytime there’s a tradeoff, the body gets the short end of the stick. Therefore, the reproductive cells evolved perpetuate themselves forever, but our bodies evolved as temporary vehicles, made to pass on the reproductive cells and then die.<br> <br> All this depends on a distinction between bodily cells and reproductive cells, a distinction that researchers first noticed more than a century ago: the bodies are mortal but reproductive cells are “immortal” in the same way that bacteria supposedly were.<br> <br> In fact, it has been “almost an article of faith” for most of this time that aging couldn’t occur in organisms that had a distinction between reproductive cells and body cells, wrote Kirkwood, in an upcoming commentary for the research journal Mechanisms of Aging and Development.<br> <br> But recent findings have steadily eroded this assumption. The latest finding of aging in E. Coli is only most dramatic of these.<br> <br> This doesn’t mean the previous theories are incorrect, but the emphasis may have to change, researchers said. It may be that aging, rather than being a way to shift resources from old organisms to young ones, is a way for organisms to get rid of worn-out parts of themselves.<br> <br> When E. Coli divides, each “daughter cell” inherits half of the “mother cell,” plus a new half that is created to go along with it. There is thus an old half and a new half. When the daughter cells divide, those “old halves” go into their own daughter cells, and so forth. The old halves keep getting older.<br> <br> The new findings, by Eric Stewart and colleagues at the National Institute in Paris, found that cells containing the oldest halves grow slower, and reproduce less. A few seem to stop reproducing completely.<br> <br> It may be that the old halves contain cellular structures thatare worn out or damaged, and it either impossible to fix it or not worth the costs, the researchers wrote. Thus the aging process may be a way for the cells to get rid of damaged parts of themselves.<br> <br> “These results suggest that no life strategy is immune to the effects of aging, and therefore immortality may be either too costly or mechanistically impossible in natural organisms,” the researchers wrote in their study, published in the February issue of the research journal Public Library of Science—Biology.<br> <br> This may dampen the prospects for finding cures to aging, Stewart said. But it may also better researchers to understand aging, and fight it better, because it helps to have a simple organism such as E. Coli in which to study these processes. “That nature may not have evolved an immortal organism doesn’t mean that science can’t significantly increase human life span,” he wrote in a recent email.</font></p> </b> </body>