Physiology
The bacteria exhibit many unusual characteristics, mostly due to the adaptations necessary for their large size. Epulopiscium is extremely polyploid, with bacterial chromosomes representing as much as 100,000–200,000 copies of the genome throughout the cell at any given time. Since bacteria rely on diffusion rather than cytoskeletal transport as in eukaryotes, this over-expression may be necessary for proteins to disperse throughout the cell. This polyploidy is also associated with a very high efflux rate, due to the over-expression of genes for export pumps.
Epulopiscium has a unique anatomy that helps it overcome the size limitations inherent in cell volume. Its cell wall contains many folds in order to increase surface area, and it possesses an unusual "cortex" containing tubules, vesicles, and other structures which are usually found in eukaryotes. It may be the case that these structures are involved in intracellular transport, which would provide a unique example of convergent evolution on the cellular level.
While these adaptions allow the bacteria to break the theoretical upper limit for size, the underlying evolutionary reasons for the bacteria to grow to this size in the first place remain speculative. One possible reason could be the ability to avoid predation by protists.
Read more about this topic: Epulopiscium Fishelsoni
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