There are nearly one trillion species on the Earth while 99.999 percent of species still remain undiscovered, the largest-ever analysis of microbial data has revealed.
Biologists from Indiana University have combined microbial, plant and animal community datasets from government, academic and citizen science sources, resulting in the largest compilation of its kind.
Altogether, the data represents over 5.6 million microscopic and non-microscopic species from 35,000 locations across all the world's oceans and continents, except Antarctica.
Estimating the number of species on the Earth is among the great challenges in biology.
"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," said associate professor Jay T Lennon.
The advent of new genetic sequencing technology provides an unprecedented large pool of new information, he added.
These data sources pull together 20,376 sampling efforts on bacteria, archaea and microscopic fungi and 14,862 sampling efforts on communities of trees, birds and mammals.
"This research offers a view of the extensive diversity of microbes on Earth. It also highlights how much of that diversity still remains to be discovered and described," added Simon Malcomber, director of the National Science Foundation's Dimensions of Biodiversity programme.
The estimate, based on the intersection of large datasets and universal scaling laws, appeared in the journal Proceedings of the National Academy of Sciences.
The results suggest that actually identifying every microbial species on the Earth is an almost unimaginably huge challenge.
To put the task in perspective, 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," Lennon said.
"The 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," the authors noted.
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