Scientists discover complex bacteria bigger than a fruit fly

Carrying its DNA in a membranous pouch.
Loukia Papadopoulos
Scanning electron microscopy observation of an individual Thiomargarita magnifica.BioRxiv

Bacteria are the stuff of nightmares but we can take solace in the fact that they tend to be quite small, in fact, invisible to the naked eye.

Not anymore! Scientists have discovered a bacterium that is bigger than a fruit fly, according to a report by Science published on Wednesday.

The researchers also report being amazed by the bacterium's complexity.

A big bacteria

You might think that being so large the bacterium would be multi-celled but it is indeed still a single-celled organism. It can, however, grow up to 0.78 inches (2 centimeters) long and is shaped like a string.

In addition, it has another strange peculiarity that distinguishes it from most other bacteria: it carries all its genetic material inside a membranous pouch whereas most other bacteria leave their DNA floating around. As such, the microbe can be categorized somewhere between a prokaryote and a eukaryote.

Prokaryotes are organisms that lack a distinct nucleus and other organelles due to the absence of internal membranes while eukaryotes, such as animals, plants, and fungi, contain a nucleus and other membrane-bound organelles. 

"All too often, bacteria are thought of as small, simple, 'unevolved' life-forms — so-called 'bags of proteins,'" Chris Greening, a microbiologist at Monash University who was not part of the new research, told Science.

"But this bacterium shows this couldn't be much further from the truth."

A second pouch

The new bacteria was also found to be carrying a second pouch filled with water that makes up more than 70 percent of its total volume. This trait is quite similar to a bacteria in the genus Thiomargarita that also carries the same kind of pouch.

After a genetic analysis was conducted, the researchers deduced that the newly-discovered bacterium likely belongs to the same genus and called it T. magnifica. Naming it does not make it any less scary as we are certain this humongous bacteria will haunt our dreams.

The research was published in the preprint database bioRxiv on February 18.

Study abstract:

Cells of most bacterial species are around 2 µm in length, with some of the largest specimens reaching 750 µm. Using fluorescence, x-ray, and electron microscopy in conjunction with genome sequencing, we characterized Ca. Thiomargarita Magnifica, a bacterium with an average cell length greater than 9,000 µm that is visible to the naked eye. We found that these cells grow orders of magnitude over theoretical limits for bacterial cell size through unique biology, 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 in daughter cells. These features, along with compartmentalization of genomic material and protein synthesis in membrane-bound organelles, indicate a gain of complexity in the Thiomargarita lineage and challenge traditional concepts of bacterial cells.

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