Planctomycetes: Their Evolutionary Implications for Models for Origins of Eukaryotes and the Eukaryote Nucleus and Endomembranes

Abstract

Planctomycetes and their relatives in the PVC superphylum have significant implications for evolution of the diversity of bacterial and eukaryotic cell organisation. The compartmentalisation via internal membranes of an underlying plan shared by planctomycetes and by members of phyla Verrucomicrobia and Lentisphaerae within the PVC superphylum implies phylogenetic meaning to such structure. It is likely that the common ancestor of PVC superphylum members possessed such compartmentalisation. Compartmentalisation in PVC bacteria, especially within the Gemmata clade where the nucleoid is bounded by an envelope of two membranes, has implications for theories of the origin of the eukaryotic nucleus, suggesting autogenous theories should be considered seriously as major alternatives to those depending on early fusions between Archaea and Bacteria domains. Explanations for the origin of PVC compartmentalisation are considered here, as well as their implications for molecular correlates of such compartmentalisation, and their correlates with an integrated cell biology that may be an analogue or even a homologue of an ancient eukaryote cell biology. PVC bacteria can form major experimental models for exploring what such a cell biology might have looked like.