A team of scientists has discovered a marine microorganism so simple that it barely has the essentials to remain alive. This is candidatus sukunaarchaeum mirabile, an archea that has broken the record of the genome smaller known among the autonomous cells, and that could change the way we understand the limits of life.
This tiny being was found inside a marine microalgae, where he lives associated with other microbes. The surprising thing is that its genome measures only 238 thousand pairs of bases, almost half than the previous record, the Nanoarchaeum Equitans, with 490 thousand. This means that Sukunaarchaeum has an extremely reduced set of genes.
As experts from the National Autonomous University of Mexico (UNAM) explained, this microbe lacks almost all the functions that we usually consider basic for a living being: it cannot produce amino acids, or generate energy by itself. Their genes focus almost exclusively on copying their DNA and manufacturing proteins, just to multiply. In essence, its only function seems to be replicated.
The most curious thing is that, despite its simplicity, Sukunaarchaeum is not a virus. Unlike these, it has ribosomes and other elements that allow it to manufacture its own proteins, although it depends totally on the environment within its guest to survive.
This discovery was made thanks to a study that analyzed the DNA of all the microbes present in a single marine seaweed cell. The scientists found, among other genomes, a circular, very small and unknown. With advanced sequencing techniques they managed to rebuild it and verify that it was an archea never seen before.
When analyzing their genetic information, researchers saw that more than 70% of their known genes are dedicated to DNA management and protein production. It practically does not have genes to perform metabolic functions, which indicates that it depends completely on the nutrients of its host.
Scientists also found sequences similar to those of Sukunaarchaeum in different samples of world oceans, suggesting that it is not an isolated case: there could be a broader group of microbes that live in a similar way, completely dependent on other cells.
This finding not only beats a record, but it challenges our ideas about what is the minimum of a cell to live. It reveals a microbial world still full of secrets, in which life can adopt much simpler and strange forms than we imagined.