One gram of soil: a microbial biochemical gene library.

One gram of soil is an immense biochemical gene library producing diverse genetic instructions, which have been present for almost 4 billion years on the Earth. There is sufficient DNA in 1 g of soil to extend 1,598 km. However, this is certainly an underestimate for fertile soils. Can the amount of genetic information contained in one g of soil be accurately estimated? The answer is not always definitive as the estimate depends on the particular g of soil being researched and the methods for DNA extraction, purification and quantification. Moreover, there is no such entity as a typical or average g of soil. Extraction of DNA from soil samples is never 100% efficient and can vary from a few microg to almost 200 microg DNA per g dry weight soil. However, estimates can be made that lead to a better understanding of the immense biochemical gene library and gene expression (combined transcription and translation) in microorganisms within a single g of soil. Accurate estimates of genes expressed in a single g of soil under a multitude of changing, environmental, conditions still requires considerable research. In this article, soil as a biochemical gene library, gene expression, and the minimal number of genes for the first bacteria in the environment will be examined.