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Species of Microorganisms

Microorganism / April 22, 2019

Earth could contain nearly 1 trillion microbial species, with only one-thousandth of 1 percent now identified, a new study suggests.

To come up with the estimate, researchers combined microbial, plant, and animal community datasets from government, academic, and citizen science sources.

Actinomyces israelii

Altogether, these data represent more than 5.6 million microscopic and nonmicroscopic species from 35, 000 locations from all the world’s oceans and continents, except Antarctica.

“Estimating the number of species on Earth is among the great challenges in biology, ” says Jay T. Lennon, associate professor of biology at Indiana University and coauthor of the the study that is published in the .

“Our study combines the largest available datasets with ecological models and new ecological rules for how biodiversity relates to abundance. This gave us a new and rigorous estimate for the number of microbial species on Earth.

“Until recently, we’ve lacked the tools to truly estimate the number of microbial species in the natural environment. The advent of new genetic sequencing technology provides an unprecedentedly large pool of new information.”

Microbial species are all forms of life too small to be seen with the naked eye, including all single-celled organisms, such as bacteria and archaea, as well as certain fungi. Many earlier attempts to estimate the number of species on Earth simply ignored microorganisms or were informed by older datasets that were based on biased techniques or questionable extrapolations, Lennon says.

“Older estimates were based on efforts that dramatically under-sampled the diversity of microorganisms. Before high-throughput sequencing, scientists would characterize diversity based on 100 individuals, when we know that a gram of soil contains up to a billion organisms, and the total number on Earth is over 20 orders of magnitude greater.”

‘Unimaginably huge challenge’

The realization that microorganisms were significantly under-sampled caused an explosion in new microbial sampling efforts over the past several years, including the collection of human-related microorganisms by the National Institutes of Health’s Human Microbiome Project; marine microorganisms by the Tara Oceans Expedition; and aquatic, terrestrial and host-related microorganisms by the Earth Microbiome Project.

These data sources—and many others—were compiled to create the inventory used in the current study, which pulls together 20, 376 sampling efforts on bacteria, archaea and microscopic fungi and 14, 862 sampling efforts on communities of trees, birds, and mammals.

“A massive amount of data has been collected from these new surveys, ” says postdoctoral fellow Ken Locey, whose work included programming required to compile the inventory. “Yet few have actually tried to pull together all the data to test big questions.

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