Our planet could contain roughly 1 trillion microbial species, with only 0.001% now identified, says a duo of scientists at Indiana University.

Dr. Kenneth Locey and Dr. Jay Lennon, both from the Indiana University’s Department of Biology, combined microbial, plant and animal community datasets from different sources, resulting in the largest compilation of its kind.

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

“Our study combines the largest available datasets with ecological models and new ecological rules for how biodiversity relates to abundance,” Dr. Lennon said.

“This gave us a new and rigorous estimate for the number of microbial species on Earth.”

According to the team, 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,” Dr. Lennon said.

The realization that microorganisms were significantly under-sampled caused an explosion in new microbial sampling efforts over the past several years.

“A massive amount of data has been collected from these new surveys. Yet few have actually tried to pull together all the data to test big questions,” Dr. Locey said. “We suspected that aspects of biodiversity, like the number of species on Earth, would scale with the abundance of individual organisms.”

“After analyzing a massive amount of data, we observed simple but powerful trends in how biodiversity changes across scales of abundance,” the scientists said.

“One of these trends is among the most expansive patterns in biology, holding across all magnitudes of abundance in nature.”

The study results, published in the Proceedings of the National Academy of Sciences, also suggest that actually identifying every microbial species on Earth is a huge challenge.

“The Earth Microbiome Project — a global multidisciplinary project to identify microscope organisms — has so far cataloged less than 10 million species. Of those cataloged species, only about 10,000 have ever been grown in a lab, and fewer than 100,000 have classified sequences,” Dr. Lennon said.

“Our results show that this leaves 100,000 times more microorganisms awaiting discovery — and 100 million to be fully explored. Microbial biodiversity, it appears, is greater than ever imagined.”

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Kenneth J. Locey & Jay T. Lennon. Scaling laws predict global microbial diversity. PNAS, published online May 2, 2016; doi: 10.1073/pnas.1521291113