Our planet may be home to a staggering 1 trillion microbial species – 99.999 percent of which remain unearthed, according to a new study.

Two biologists from Indiana University – associate professor Dr. Jay Lennon and postdoc fellow Dr. Kenneth Locey – created the biggest microorganism database of its kind by using combined animal, plant, and microbial data from government, academic, and citizen science records. The output: an estimate of more than 5.6 million identified species from 35,000 places across the world except Antarctica.

They then applied mathematical scaling laws to predict the number of species at a certain landscape. They discovered that across communities of both microscopic and larger plant/animal groups, the same scaling laws applied: as the number of organisms in a given community increased, the number of species grew.

"Until now, we haven't known whether aspects of biodiversity scale with something as simple as the abundance of organisms. As it turns out, the relationships are not only simple but powerful, resulting in the estimate of upwards of 1 trillion species,” said Locey.

Lennon said estimating the number of species on the planet is among biology’s greatest challenges today, with new genetic sequencing methods only recently offering a large pool of new information.

“We’ve done a pretty good job of cataloguing macrobes . . . but the rate we are exploring new [plants and animals] is slowing down,” he told Christian Science Monitor, also citing that it is only in the last two to three decades that scientists learned how to identify microbes.

Microbes are the most abundant life on Earth, meaning biologists are still missing out on a huge chunk of their population. These species include single-celled organisms like bacteria and archaea and certain types of fungi, with 10,000 varying kinds of bacteria on 1 square centimeter (0.155 square inch) of a human arm at any time.

Moreover, humans greatly rely on these microbes for a rich array of functions, including digestion, nutrient cycling, and clean water. There could be many more roles these organisms play in everyday life but haven’t been recognized as such.

The significantly undersampling of microorganism has led to new efforts in the last few years, including the collection of the Human Microbiome Project of the National Institutes of Health and the Tara Oceans Expedition’s marine microorganisms.

“[This research] highlights how much of that diversity still remains to be discovered and described,” echoed Simon Malcomber of the National Science Foundation’s Dimensions of Biodiversity, which funded the study. Despite this gap, he added, about 40 percent of the global economy keeps depending on biological resources.

Malcomber delved on the “sheer diversity” of microorganisms around and how little is known about them, encouraging increased efforts in documentation and understanding their myriad roles in world ecosystems.

There is a gargantuan – if not outright impossible – task ahead of identifying every microbial species on the planet. The international, interdisciplinary initiative Earth Microbiome Project, for example, has catalogued less than 10 million species so far.

Of these recorded species, only around 10,000 have ever been lab-cultivated, while fewer than 100,000 have classified sequences, Lennon expanded, their results indicating that 100,000 times more microbes are awaiting discovery.

Canadian professor Dr. Laura Hug said genome-based techniques in the last 20 years will help science dig deeper into microbial DNA. Recently, Dr. Hug also published a paper identifying 1,000 previously undetected microbes – also made possible by a scientific breakthrough.

The findings were published Monday in the journal Proceedings of the National Academy of Sciences.

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