Spatially segregated transcription and translation in cells of the endomembrane-containing bacterium Gemmata obscuriglobus

Abstract

The dogma of coupled transcription and translation in bacteria has been challenged by recent reports of spatial segregation of these processes within the relatively simple cellular organization of the model organisms Escherichia coli and Bacillus subtilis. The bacterial species Gemmata obscuriglobus possesses an extensive endomembrane system. The membranes generate a very convoluted intracellular architecture in which some of the cell's ribosomes appear to have less direct access to the cell's nucleoid(s) than others. This observation prompted us to test the hypothesis that a substantial proportion of G. obscuriglobus translation may be spatially segregated from transcription. Using immunofluorescence and immunoelectron microscopy, we showed that translating ribosomes are localized throughout the cell, with a quantitatively greater proportion found in regions distal to nucleoid(s). Our results extend information about the phylogenetic and morphological diversity of bacteria in which the spatial organization of transcription and translation has been studied. These findings also suggest that endomembranes may provide an obstacle to colocated transcription and translation, a role for endomembranes that has not been reported previously for a prokaryotic organism. Our studies of G. obscuriglobus may provide a useful background for consideration of the evolutionary development of eukaryotic cellular complexity and how it led to decoupled processes of gene expression in eukaryotes.

Nuclear pore-like structures in a compartmentalized bacterium

“…pore structures) for macromolecules passing between the internal compartments and the rest of the cytoplasm. This hypothesis is consistent with the recent finding of confinement of translation to nonnucleoid regions of G. obscuriglobus cells [13]. A corollary of our study of G. obscuriglobus internal compartments was that several different types of membranes might be isolatable from lysed cells, and we have confirmed this concept here.…”

“…The functional distribution is similar to the BLAST results: A large fraction are hypothetical (51), unnamed (7) and probable (3), while annotated functions include flagellar (6), ribosomal (13), efflux (4) and membrane (5) hits. Notably, PHMMER and BLASTP find the exact same top hits for 64/128 proteins.…”

“…ATP synthase was found only in this cytoplasmic membrane fraction (fraction 6) and in the vesicle-enriched membrane fraction (fraction 2), and not in the pore-containing membrane fraction (fraction 3). This indicates that the 13 function of the pore-containing membranes is probably not that of electron transport or energy generation. In the pore-containing membranes (fraction 3), we identified 128 proteins, 39 (30.5%) of which were unique to this fraction (S2 Table).…”

Determining the bacterial cell biology of Planctomycetes

“…1) or to vesicles within the paryphoplasm1516. Eukaryotic MCs such as clathrins play a major role in the formation of coated vesicles during endocytosis and display similar localizations to those in Planctomycetes14. Endocytosis is considered as a hallmark of eukaryotes because it is presumed to have paved the way for the acquisition of an endosymbiont.…”

Evolutionary gradient of predicted nuclear localization signals (NLS)-bearing proteins in genomes of family Planctomycetaceae

“…Moreover, nearly all of the “unique” characteristics beyond non-planctomycete bacteria in Planctomycetaceae have been argued not relevant to homology with eukaryotic characteristics, with many of them proposed to result from convergent evolution or lateral gene transfer [15]. Arguing on the other hand in favor of potential homology is the finding that ICMs divide cells of all examined planctomycete species into two compartments, the paryphoplasm and pirellulosome [16, 17], and consequently may make transcription and translation independent, allowing for the development of eukaryotic cellular complexity [18]. The exact nature and topology of planctomycete cell compartments has been subject to controversy, and the question of a closed nucleoid-associated membrane envelope is especially subject to debate [19, 20] - compartments completely closed by membranes may however imply some form of transport system similar to that used by eukaryotes for nucleocytoplasmic transport.…”