What makes us different from bacteria? On the cellular level, one of the main differences is that, while eukaryotic cells such as our own (and those of plants and other animals) are compartmentalized by internal membranes, bacteria have a single compartment, with their genetic material mixing freely with the cytoplasm.
At least, that was the conventional wisdom, until Evgeny Sagulenko from the University of Queensland, Australia, and colleagues published a paper describing a group of marine bacteria called planctomycetes. They showed that planctomycetes are in fact like eukaryotes in having internal compartments that separate their genetic material from the rest of the cell. Nonetheless, the membranes enclosing such compartments had not been analyzed in any detail.
Now, Sagulenko and colleagues explore these fascinating bacteria a little more closely in a new study. The researchers examined the internal membranes of the planctomycete species Gemmata obscuriglobus, using various electron microscopy methods to analyse the structures embedded in these membranes.
Sagulenko found that the internal membranes of G. obscuriglobus contain embedded pore-like protein complexes whose structure is similar to that of pores found in the eukaryotic nucleus, and may be the first such structures found in bacteria. Like eukaryote nuclear pores, the bacterial structures contain a basket structure, spokes and eight-fold rotational symmetry. Some of the proteins associated with the complexes even contain the same structural domains as eukaryote nuclear pore proteins. The similarities are obvious when comparing the structures side-by-side (see image).
It is not clear whether eukaryotic nuclear pores evolved from these similar bacterial pore-like structures or whether the two structures evolved separately, and more detailed analysis of the structures would be needed to help determine their evolutionary origin. Nonetheless, this may be the first description in bacteria of a nuclear pore-like structure, once believed to be the sole preserve of eukaryotes.
Gemmata obscuriglobus has been called the “platypus of microbiology” because of its unusual compartmentalization, a characteristic more commonly found in an entirely different evolutionary group. This new discovery of nuclear pore-like structures serves to make it even more different from most of its bacterial relatives than previously thought.
Research Article: Sagulenko E, Nouwens A, Webb RI, Green K, Yee B, Morgan G, et al. (2017) Nuclear Pore-Like Structures in a Compartmentalized Bacterium. PLoS ONE 12(2): e0169432. doi:10.1371/journal.pone.0169432
Images Credits: Sagulenko et al.; Adapted from original Artwork created for Wikipedia by Mike Jones, uploaded by R. S. Shaw, and Sagulenko et al.