We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is the Simplest Organism Known?

Michael Anissimov
Updated May 21, 2024
Our promise to you
All The Science is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At All The Science, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Which microbe is the simplest organism depends on your definition of a living organism. If viruses, prions, satellites, nanobes, nanobacteria (non-free-living sub-bacterial organisms) are excluded, the simplest free-living organism known is Mycoplasma genitalium, with a genome of only 580,000 base pairs and 482 protein-coding genes. Mycoplasma genitalium is a tiny parasitic bacteria that lives in the digestive and genital tracts of primates.

By comparison, Carsonella ruddii, an endosymbiotic bacteria that lives in plant lice, has a genome of only 159,662 base pairs, with just 182 genes, the smallest known. However, Carsonella ruddii cannot live on its own, and like a virus, depends on the host to survive. Previously, a thermophile that lives around underwater hot springs, Nanoarchaeum equitans, was thought to be the simplest organism, with a genome 490,885 base pairs long and a size of 400 nanometers.

Mycoplasma genitalium and other "ultramicroscopic" bacteria have diameters in the ballpark of 200-300 nanometers, smaller than some large viruses. 200 nm is about the limits of a conventional light microscope, so an electron microscope or atomic force microscope is necessary to observe these organisms. There may be free-living organisms even smaller than this — so-called nanobacteria or nanobes are around 10 - 20 nanometers in size, although their status as living organisms is controversial. No DNA has yet been successfully extracted from these objects, which may simply be mineral growths. On the other hand, among them may be the world's simplest organism.

Viruses, which cannot reproduce independently, are of course smaller and simpler than bacteria. Some of the smallest RNA viruses, retroviruses such as the Rous sarcoma virus, have genomes 3,500 base pairs in length, a diameter of about 80 nm, and only possess just four genes. The smallest DNA viruses have a smaller size (18-26 nm) but larger genomes, around 5,000 base pairs. Bacteria and viruses with tiny genomes tend to have a high ratio of protein coding genes (95-98%), in comparison to larger genomes like the human genome, where only 1.5% of genes code for proteins.

In an interesting twist on the simplest organism story, scientist Craig Venter Nobel Prize winner Hamilton Smith, working at the J. Craig Venter Institute are attempting to create an even simpler organism, Mycoplasma laboratorium, which, if successful, will also be the first example of synthetic life. Taking a Mycoplasma genitalium as a starting point, the team randomly knocks out genes and observes the resulting organism for signs of life. Venter believes that 100 of the 482 protein-coding genes in Mycoplasma are redundant, and seeks to synthesize a novel genome from scratch containing only 382 genes, then inject it into a gutted Mycoplasma genitalium, which would then reanimate, Frankenstein-style. This is called the Minimal Genome Project. The goal is to use the simplest organism to produce large amounts of hydrogen for renewable fuel.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By Logicfest — On Jan 27, 2014

Good for you on pointing out the Minimal Genome Project. This one holds a lot of promise to create enough hydrogen to meet our fuel needs and that is a good thing.

On a side note, it is my understanding that the richest source to use for mining hydrogen is petroleum. Uh, that's more than a bit counterproductive, isn't it?

While it is true that hydrogen is available in abundance, separating it from something else (such as water) has proven to be expensive and time consuming. Having something that will generate pure hydrogen for use in alternative fuels would be a very solid step in the right direction.

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
Learn more
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.