Thiomargarita magnifica

Thiomargarita magnifica is a species of sulfur-oxidizing gammaproteobacteria, found growing underwater on the detached leaves of red mangroves from Guadeloupe archipelago in Lesser Antilles. This filament-shaped bacterium is the largest ever discovered, with an average length of 10 mm and some organisms reaching 20 mm.[1] The bacterium is described in a preprint published in February 2022.[2] The organism was originally discovered in early 2010s by Olivier Gros from the University of the French Antilles at Pointe-à-Pitre, but initially did not attract much attention (Gros at the time thought his find to be a fungus[3]); it took Gros and other researchers 5 years to find out that this is actually a bacterium, and few more years until Jean-Marie Volland, a graduate student working for Gros, figured out its unusual properties.[1]

Thiomargarita magnifica
Scientific classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Gammaproteobacteria
Order: Thiotrichales
Family: Thiotrichaceae
Genus: Thiomargarita
Species:
T. magnifica
Binomial name
Thiomargarita magnifica
Volland et al., 2022

Thiomargarita means "sulfur pearl". This refers to the appearance of the cells; they contain microscopic sulfur granules that scatter incident light, lending the cell a pearly lustre.

Encapsulated DNA

The discovery of T. magnifica is important as it blurs the boundary between prokaryotes, primitive single-cell organisms that do not have a cell nucleus (their DNA is free-floating), and eukaryotes, where the DNA is surrounded by the nuclear envelope. With T. magnifica being a bacterium, it belongs to prokaryotes, but its cell includes membrane sacs that encapsulate the cell's DNA.[1]

Structure

Metabolism in bacteria can only occur through the diffusion of molecules of both nutrients and waste through the interior of the bacteria cells, and this places an upper limit on the size of these organisms. The large sulfur bacterium T. namibiensis, discovered in 1999, overcomes this limit by including a large sac filled with water and nitrates. This sac pushes the cell contents to the cell wall, so that the diffusion can work; the life only happens "along the edge" of the cell. T. magnifica's cell includes a similar vacuole[1] that occupies most of the cell (65-80 % by volume) and pushes the cytoplasm to the periphery of the cell (the thickness of cytoplasm varies from 1.8 to 4.8 microns).[2]

The outside of the cell lacks epibiotic bacteria, their "surprising absence" can be explained by T. magnifica possibly producing biologically active or even antibiotic chemical compounds.[2]

Notes
  1. Pennisi, Elizabeth. "Largest bacterium ever discovered has unexpectedly complex cells". Science. science.org. Retrieved 24 February 2022.
  2. Volland, Jean-Marie; Gonzalez-Rizzo, Silvina; Gros, Olivier; Tyml, Tomáš; Ivanova, Natalia; Schulz, Frederik; Goudeau, Danielle; Elisabeth, Nathalie H; Nath, Nandita; Udwary, Daniel; Malmstrom, Rex R; Guidi-Rontani, Chantal; Bolte-Kluge, Susanne; Davies, Karen M; Jean, Maïtena R; Mansot, Jean-Louis; Mouncey, Nigel J; Angert, Esther; Woyke, Tanja; Date, Shailesh V (18 February 2022), A centimeter-long bacterium with DNA compartmentalized in membrane-bound organelles, Cold Spring Harbor Laboratory, doi:10.1101/2022.02.16.480423, S2CID 246975579
  3. Rogers, Peter. ""Impossibly big" bacteria rattle the field of microbiology". BigThink. Retrieved 22 March 2022.
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