9.C.13 The Eukaryotic and Bacterial Endocytosis (EBE) Family

Endocytosis is a process by which extracellular material such as macromolecules can be incorporated into cells via a membrane-trafficking system. Thus, endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Endocytosis includes pinocytosis and phagocytosis (Hallett 2020). Endocytic pathways have been described for slime molds (Vines and King 2019), animals ((Hartenstein and Martinez 2019; Rudolf and Straka 2019) plants (Fan et al. 2015; Ivanov and Vert 2020), fungi (Dimou and Diallinas 2020), and single celleds eukaryotes (Wideman et al. 2014). The machinery for endocytosis of the epidermal growth factor receptor coordinates the transport of incoming hepatitis B virus to the endosomal network ((Iwamoto et al. 2020). We refer to such endocytic mechanisms as Bulk Transport, and this topic is not covered in detail in TCDB which focuses on molecular transport. Endocytosis of nutrient transporters in fungi provides a mechanism of regulating nutrient uptake, and this topic has been reviewed (Barata-Antunes et al. 2021).

Although universal among eukaryotes, endocytosis has only recently been identified in Bacteria or Archaea. Intracellular membranes are known to compartmentalize cells of bacteria in the phylum Planctomycetes, suggesting the potential for endocytosis and membrane trafficking in members of this phylum. Lonhienne et. al, (2010) showed that cells of the planctomycete Gemmata obscuriglobus have the ability to take up proteins present in the external milieu in an energy-dependent process analogous to eukaryotic endocytosis, and that internalized proteins are associated with vesicle membranes. Occurrence of such an ability in a bacterium is consistent with autogenous evolution of endocytosis and the endomembrane system in an ancestral noneukaryotic cell.