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Comment by sva_ | Hacker News Reader

The article seems to imply that this organism is single-cellular:

> Its threadlike single cell is visible to the naked eye, growing up to 2 centimeters—as long as a peanut—and 5000 times bigger than many other microbes.

The study[0] however speaks of "cells" in plural, and "daughter cells". It would've really surprised me if that really had been a single cell - unless I'm misunderstanding something here.

edit: I stand corrected. Misunderstood it.

[0] from other comment: https://www.biorxiv.org/content/10.1101/2022.02.16.480423v1....

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No, they claim that most of the filament is a single cell, albeit with compartmentalized DNA:

> Strikingly, all techniques consistently showed that each filament was one continuous cell for nearly its entire length with no division septa, including the partial constrictions towards the apical pole. Only the most apical few buds were separated from the filament by a closed constriction and represented daughter cells

"Apical" means the apex of the filament. In other words, toward the end of the filament the cell starts pinching off ("budding") to create daughter cells as part of its reproductive cycle. But the away from the end, the cell is contiguous. Fig. S2 is highly recommended.

Believe it or not, that's not even close to the largest unicellular organism. One of the largest is Valonia ventricosa, a species of algae that has spherical or ovoid cells "with a diameter that ranges typically from 1 to 4 centimetres (0.4 to 1.6 in) although it may achieve a diameter of up to 5.1 centimetres (2.0 in) in rarer cases." [0]

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[0]: https://en.wikipedia.org/wiki/Valonia_ventricosa#Physiology_...

My favorite large unicellular organisms are Xenophyophorea. They have multiple nuclei probably because the diffusion of transcription processes over an 8 inch diameter cell would be just too slow with a single central nucleus.

https://en.wikipedia.org/wiki/Xenophyophorea

Point being those algae are eukaryotic. The article is about an unusually large bacterium (prokaryotic) which has some eukaryotic features.

First subheading of the study: "Thiomargarita magnifica is a centimeter-long, single bacterial cell". They apparently stick together, but do constitute individual organisms.

There is precedence for cells being that large. I can't remember the organism name, but there is actually some macroscopic single cell organism. It cheats by having multiple nuclei, among other things.

You may be thinking of Valonia ventricosa (bubble algae), though I believe there are others.

Chicken and ostrich eggs are both single cells that are quite large as well

But it's an eukaryote cell. Not prokaryote.

Yeah, but the cell of such single-celled organisms are usually round or in one segment. This one looks like it has several segments, and still be a single cell, which is fascinating. Perhaps it is blurring the line between single cellular and multi cellular a bit, which might be the point that the article was trying to make.

What is new here is that this is a bacteria, not a nucleate cell. Large eukaryote cells, even over 10 cm (4 inches), are well known. Almost all normal bacteria have a diameter under 100 micrometer, usually much less.

The article explains that the huge size for a bacteria seems to be enabled by 2 features, first a large water-filled vesicle inside, so that the living part of the cell is around the periphery of the cell, within short distances from the cell membrane, and second, a special compartment for DNA which provides some of the functions of a nucleus in an eukaryote (nucleate) cell.

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