Gemmata obscuriglobus is one of a strange class of organisms with features from multicellular life forms that are still classed as bacteria. This anomaly has inspired the nickname the “platypus of microbiology”, after the egg-laying mammal. A new study has identified tiny formations inside G. obscuriglobus that look like pores found within animal and plant cells. Their function is yet to be determined, but the pores may prove key to explaining one of the most important evolutionary developments.
The tree of life has three great branches: Eukaryota includes plants, animals, and fungi, while Bacteria and Archaea (together called prokaryotes) represent the other two taxon. Although the eukaryotes we are most familiar with, ourselves included, are composed of many cells, single-celled eukaryotes also exist. Eukaryotes are distinguished from prokaryotes by organelles such as the cell nucleus enclosed within a membrane, which provides separation from the rest of the cell.
What then to make of bacteria that contain internal membranes that form their own closed compartments? Microbiologists have been pondering this since the Planctomycetes were first discovered. Emeritus Professor John Fuerst of the University of Queensland has added to this debate with the announcement in PLOS One of pores on the internal membranes of G. obscuriglobus that resemble eukaryote nuclear pores. In both cases, the pores have a basket structure, spokes, and eight-fold rotational symmetry.
“Eukaryote nuclear pores allow the transport of proteins into the nucleus and RNA out,” Fuerst told IFLScience. “We have no idea what they do in this case, but it is likely to involve the transport of macromolecules.”
At the moment, so little is known about G. obscuriglobus' internal membranes that we are not even sure if they form closed structures. However, Fuerst thinks the discovery of the pores increases the likelihood that they do, and points to other members of the Planctomycetes where this has been confirmed.
The importance of the discovery lies in the possibility that such compartmentalized bacteria cells might provide a model for the evolution of the nucleus, which in turn made possible the appearance of multicellular life.
Fuerst explained to IFLScience that there is much debate as to whether the internal structures of G. obscuriglobus and its ilk are surviving examples of the evolutionary path that led to eukaryote nuclei, or if the similarities represent convergent evolution, where similar circumstances produce analogous outcomes.
Either way, Fuerst thinks these membranes can reveal a stepping stone to the development of full nuclei, and the more similar these features are, the more we stand to learn.
G. obscuriglobus was discovered in a Queensland dam in 1984. Other members of the Gemmata genus occupy niches as diverse as Australian soil and wastewater from a French hospital.