Estimating the number of bacterial species is impossible with current technology. Using DNA reassociation and mathematical models, estimates range from 10 million to 1 billion species. Sequencing fragments is more cost-effective than whole genomes, and one survey found 20,000 species in 1 quart of seawater.
Estimating the exact number of species of bacteria is impossible with today’s technology. To really get close to having a target number, people would need a machine that could process soil, water, and rock in large quantities, isolate 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 US dollars and takes a few months, this is unattainable. Even if costs were to drop by a factor of a trillion, there are so many microbes in soil that classifying them this way would be prohibitively expensive.
Instead of sequencing entire genomes, bacterial investigations use fragments to distinguish between different species. This is more cost-effective than whole genome sequencing. One survey found 20,000 species of bacteria in 1 quart (about 1 litre) of seawater.
Another approach to determining the amount of bacteria in a sample is to use a technique called DNA reassociation. In DNA reassociation, scientists use chemicals to “unzip” the two strands of the double helix in bacterial DNA, then mix them. Matching DNA strands reconnect to each other. The longer the reassociation process takes, the more species are present in the sample. These time measurements can be used to estimate bacterial biodiversity in the ocean or soil.
When this technique was applied to a soil sample in the late 1990s, 16,000 species were found. This technique included the assumption that the populations of different species of bacteria were roughly similar, however, which is now known to be false. An updated survey by Jason Gans found that there are approximately one million bacterial species per 0.035 ounce (1 gram) of soil. While only a few bacterial species dominate the soil, there are a huge number of low-abundance species.
Another approach is to use mathematical models of species diversity curves to extrapolate the total number of species in a given sample from information on the abundance of a few major species. A 2002 article by Curtis, Sloan, and Scannel, “Estimating Prokaryotic Biodiversity and Its Limits,” estimated the number of oceanic bacterial taxa to be less than 2 million, the number of soil taxa to be at least 4 million, and the number of atmospheric taxa to at least 4 million. This study assumed that the bacterial diversity in one gram of soil was only 6,400 to 38,000 per gram, much less than that found in the DNA reassociation study.
Currently, estimates of the total number of species range from about 10 million to one billion, but these estimates are tentative and could be incorrect by many orders of magnitude. By comparison, there are probably between 10 and 30 million species of animals, the vast majority of them insects. The number of scientifically recognized animal species is approximately 1,250,000. There are nearly 300,000 recognized plant species.
Protect your devices with Threat Protection by NordVPN
