Monday, July 8, 2013

How Simple Can Life Get?

In the pageant of life, we are genetically bloated. The human genome contains around 20,000 protein-coding genes. Many other species get by with a lot less. The gut microbe Escherichia coli, for example, has just 4,100 genes.

Scientists have long wondered how much further life can be stripped down and still remain alive. Is there a genetic essence of life? The answer seems to be that the true essence of life is not some handful of genes, but coexistence.

For years, M. genitalium held the record for the smallest genome. (Scientists don’t allow viruses into this contest, since viruses can’t grow and reproduce on their own.) But in recent years, M. genitalium has lost its minimalist crown. Today, the record-holder is a microbe called Tremblaya princeps, which contains only 120 protein-coding genes.

Have we found the minimal genome at last? The answer, once again, is no. But the reason for that reveals something else intriguing about life.

Tremblaya lives in one particular place: the body of a mealybug. And the mealybug, in turn, depends on Tremblaya for its survival.


- Read the whole column by Carl Zimmer (very interesting)

Studies like Dr. McCutcheon’s show that the concept of a minimal genome, while provocative, is ultimately a dead end. Life does not exist in a laboratory vacuum, where scientists can pare away genes to some Platonic purity. Life exists in a tapestry, and the species with the smallest genomes in the world survive only because they are nestled in life’s net.



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