How giant bacteria once broke the laws of nature

(ORDO NEWS) — Biologists from the California Institute of Technology have figured out what minimum and maximum sizes bacteria can reach.

Scientists have called the upper limit the ribosomal catastrophe, because too large cells need an incredible amount of RNA and ribosomes, but some bacteria were able to overcome it.

The size of various bacteria can vary by several orders of magnitude, from 0.1 micrometers in Mycoplasma mycoides, which is comparable to some large viruses, to 750 micrometers in Thiomargarita namibiensis.

The volume of bacteria increases in proportion to the cube of its linear dimensions, which means a more active metabolism, which gives large microbes an advantage in growth and reproduction. However, there are size limits that bacterial cells could not overcome.

Scientists have created a computer model that helps predict how the metabolism and composition of a cell changes with increasing cell size. To do this, biologists have estimated how much intracellular space is required for the functioning of all important components: DNA, RNA, proteins and ribosomes.

In 2016, it turned out that, according to researchers, a bacterium with a cell volume of less than 10-21 meters in a cube will not be able to exist, since biopolymers such as DNA and proteins will not fit in it. The minimum size is also limited by cell membranes.

The theoretical volume differs by only three orders of magnitude from the size of the smallest known bacteria. As for the maximum limit, the larger the bacterium, the more it requires cellular components that are necessary for the processes of gene transcription and protein synthesis, as well as supporting rapid growth and division.

In the end, this leads to the so-called ribosomal catastrophe, when the finite size of the cell requires infinite amounts of ribosomes, transfer RNA and messenger RNA. According to scientists, this happens with a volume of 10-15 cubic meters.

Interestingly, Thiomargarita namibiensis far exceeds this upper limit. Even if a rather large vacuole is removed from it, its size will still be an order of magnitude larger than the border of the ribosomal catastrophe. Scientists believe that this is facilitated by environmental conditions that favor the slow development and growth of bacteria.

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