A centimeter-long bacterium with DNA compartmentalized in membrane-bound organelles

Abstract

Cells of most bacterial species are around 2 um in length, with some of the largest specimens reaching 750 um. 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 um 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 gain of complexity in the Thiomargarita lineage, and challenge traditional concepts of bacterial cells.

Extreme Polyploidy of Carsonella , an Organelle-Like Bacterium with a Drastically Reduced Genome

“…(Firmicutes), a giant bacterium observed in the fish gut, which contains tens of thousands of genomic copies per cell ( 21 ). There appears to be a tendency that bacteria with large cell sizes to be highly polyploid, as evidenced by a recent report that Candidatus Thiomargarita magnifica, a centimeter-long bacterium, has half a million copies of the genome ( 22 ).…”

Metabolic compatibility and the rarity of prokaryote endosymbioses

“…[67, 16, 34]). Many other studies have demonstrated the plasticity of prokaryote membranes and cytoskeletal architecture [68, 69, 51, 70] suggesting the absence of phagocytosis may not be as dominant a barrier as once thought. And the continuing discovery of new functions, traits, and morphologies in prokaryotes also emphasize the importance of evaluating multiple barriers, not just phagocytosis.…”

On thresholds: signs, symbols and significance

“…, 2021). Another discovery, this one of giant bacteria with their genetic material compartmentalized into separate membranes (Volland et al. , 2022) may similarly rewrite today's taxonomic distinction between prokaryotes and eukaryotes as foundational to the Tree of Life.…”

“…The recently discovered category of "giant virus" indicates that these viruses can be larger than some cellular lineages both in terms of physical size and genomic contents and are spurring reexamination of the place of the virosphere on the so-called "Tree of Life" (Harris and Hill, 2021;Koonin et al, 2021). Another discovery, this one of giant bacteria with their genetic material compartmentalized into separate membranes (Volland et al, 2022) may similarly rewrite today's taxonomic distinction between prokaryotes and eukaryotes as foundational to the Tree of Life. The exploration of protosemiosis as related to all of these discoveries is of considerable interest in understanding the origins of interpretation and classification in primitive life forms.…”