As a general rule, bacteria are usually so small that we need a microscope to see them, but the bacterium just described in the journal Science is much, much larger than anything we have ever seen. It has a single threadlike cell but so large that it is visible to the naked eye: it grows up to 2 centimeters and is 5,000 times larger than many other microbes.
This giant bacterium could be the missing link between single-celled organisms and the cells that make up humans.
A bacterium so large that it is visible to the naked eye
This giant, thread-like bacterium , native to Caribbean mangroves, can grow to about the size of a fly, pushing the boundaries of what we thought biologically possible for a single-celled organism.
It has been named Thiomargarita magnifica by an international team of researchers, including scientists from the Lawrence Berkeley National Laboratory in the US.
Having this colossal size to be a bacterium, we might think that it would be a multicellular being, but in fact it is still a unicellular organism. At 2 centimeters long and rope-like , it has a strange quirk that distinguishes it from most bacteria: it carries all of its genetic material inside a membranous bag (while most other bacteria leave their DNA floating around). .
Hence, scientists claim that it can be classified somewhere between a prokaryotic organism (simple cells, without a well-defined nucleus and whose genetic material is distributed throughout its interior) and a eukaryote (much more complex and compartmentalized cells, with a nucleus surrounded by a membrane that stores the DNA and organelles that perform different functions, such as trees and humans). And it is that, this characteristic not only distinguishes the newly discovered bacterium from other bacteria, but also distinguishes it from other prokaryotes, a group of organisms with very small and simple cell structures .
Apart from carrying its DNA in a membrane-bound bag, it also carries a second large bag filled with water, which occupies more than 70% of the cell’s total volume, the researchers report. The largest specimen observed by the researchers was 2 cm long, although they believe there could be even larger ones.
How could this bacteria grow so much?
Precisely the secret of the great size of T. magnifica may lie in the arrangement of its genetic material, which is totally atypical. We have already discussed that bacteria and other single-celled microbes called archaea are classified as prokaryotes, while multicellular organisms such as trees are classified as eukaryotes. One of the defining differences between the two is that prokaryotes have free-floating DNA, while eukaryotes package their genetic code in a nucleus.
When researchers sequenced the genome of this giant bacterium, they were amazed at its size: 11 million bases that align to form 11,000 genes . For comparison, a run-of-the-mill bacterium only has about 4 million bases and about 3,900 genes. A bacterium with an innovative biological machinery.
“Importantly, we show that centimeter-long Thiomargarita filaments represent single cells with genetic material and compartmentalized ribosomes in a new type of membrane-bound organelle. The sequencing and analysis of the genomes of five individual cells revealed information on different mechanisms of cell division and cell elongation”, the experts point out.
What does this finding mean?
The origin of complex life is one of the most important yet unanswered questions in biology.
This discovery is challenging, as it suggests that the two main branches of life are not so different after all, and that the bacterium T. magnifica could be the missing link that explains how complex life evolved from living organisms. most primitive unicellular cells more than 1 billion years ago.
“Too often, bacteria are thought of as small, simple, ‘unevolved’ life forms, so-called ‘protein bags,'” Chris Greening, a microbiologist at Monash University who was not involved in the study, explained. Science magazine. “But this bacterium shows that this couldn’t be much further from the truth.”
Referencia: Pennisi, Elizabeth (23 February 2022). “Largest bacterium ever discovered has an unexpectedly complex cell”. Science. doi:10.1126/science.ada1620. / Jean-Marie Volland A centimeter-long bacterium with DNA compartmentalized in membrane-bound organelles 2022 BioRxiv DOI: https://doi.org/10.1101/2022.02.16.480423
