Abstract
Endocytosis is a fundamental process of membrane-trafficking in eukaryotes, but has not been known to occur in bacteria or archaea. The origin of endocytosis is central to the understanding of evolution of the first eukaryotes and their endomembrane systems. In a recent study we have established that an endocytosis-like process for uptake of proteins into cells occurs in a bacterium, Gemmata obscuriglobus, a member of the distinctive phylum Planctomycetes of peptidoglycan-less budding bacteria. Members of this phylum characteristically possess cells divided into compartments separated by internal membranes and in the case of G. obscuriglobus these compartments include one where a double membrane envelope surrounds its nucleoid DNA, as well as an outer ribosome- free region of cytoplasm. Proteins can be internalized by cells from the external milieu and collected into this ribosome-free compartment, and this process is energy-dependent and appears to be receptor-mediated. As in eukaryote endocytosis, internalized proteins are associated with vesicles, and can be subjected to proteolytic degradation. The discovery of this process in a bacterium has significant implications for our understanding of the origins of endocytosis in eukaryotes.