Found: the largest bacterium discovered in the world, visible to the naked eye.

A centimeter-long bacterium with DNA contained in metabolically active, membrane-bound organelles Found: the largest bacterium discovered in the world, visible to the naked eye.

https://www.science.org/doi/10.1126/science.abb3634

Usually, bacteria cant be seen without the help of a microscope, they are about 1 µm to 5 micrometers (µms) in length. But now scientists, sampling mud in the mangrove mud of Guadeloupe, have discovered for the first time a bacterium that is visible to the naked eye. It’s by far the largest bacterium known to date as Jean-Marie Volland et. al report in a paper in the journal Science, reaching a length of up to 2 centimeters. That makes it larger than many multicellular animals. These filament-type organisms are the biggest single-cell bacteria and are, appropriately, members of a bacterial species namedThiomargarita magnifica.

A magnificent megabacterium We usually think of bacteria as microscopic isolated cells or colonies. Sampling a mangrove swamp, Volland et al. found an unusually large, sulfur-oxidizing bacterium with a complex membrane organization and predicted life cycle (see the Perspective by Levin). Using a range of microscopy techniques, the authors observed highly polyploid cells with DNA and ribosomes compartmentalized within membranes. Single cells of the bacterium, dubbed Candidatus Thiomargarita magnifica, although thin and tubular, stretched more than a centimeter in length. —MAF

Cells of most bacterial species are around 2 micrometers in length, with some of the largest specimens reaching 750 micrometers. Using fluorescence, x-ray, and electron microscopy in conjunction with genome sequencing, we characterized Candidatus (Ca.) Thiomargarita magnifica, a bacterium that has an average cell length greater than 9000 micrometers and is visible to the naked eye. These cells grow orders of magnitude over theoretical limits for bacterial cell size, display unprecedented polyploidy of more than half a million copies of a very large genome, and undergo a dimorphic life cycle with asymmetric segregation of chromosomes into daughter cells. These features, along with compartmentalization of genomic material and ribosomes in translationally active organelles bound by bioenergetic membranes, indicate gain of complexity in the Thiomargarita lineage and challenge traditional concepts of bacterial cells.