How Many Species of Bacteria Are There?
Estimating the exact number of species of bacteria is impossible with today’s technology. To really move close to having an objective number, you’d have to have a machine that could process soil, water, and rock in large amounts, isolate the bacteria from their habitat, then sequence the genomes of as many bacteria as possible within the sample. Today, given that sequencing a bacterial genome costs half a million dollars and takes a few months, this is infeasible. Even if costs fall by a factor of a trillion, there are so many microbes in soil that categorizing them in this way would be prohibitively expensive. Instead of sequencing entire genomes, bacterial surveys today merely use snippets to distinguish between different species. This is more cost-effective than whole genome sequencing. One survey found 20,000 species of bacteria in a liter of seawater. Another approach to determining the quantity of species of bacteria in a sample is to use a technique called DNA reassociation. In
