Abstract
Cyanobacteria are a group of photosynthetic prokaryotes that contribute to primary production on a global scale. These microorganisms release vesicles to the extracellular environment, spherical nanosized structures, derived essentially from the outer membrane. Even though earlier works in model Gram-negative bacteria have hypothesized that outer membrane stability is crucial in vesicle formation, the mechanisms determining vesicle biogenesis in cyanobacteria remain unknown. Here, we report on the identification of six candidate genes encoding outer membrane proteins harboring SLH/OprB-domains in the genome of the model cyanobacterium Synechocystis sp. PCC 6803. Using a genetics-based approach, one gene was found to encode an essential protein (Slr1841), while the remaining five are not essential for growth under standard conditions. Vesicle production was monitored, and it was found that a mutant in the gene encoding the second most abundant SLH/OprB protein in Synechocystis sp. PCC 6803 outer membrane (Slr1908) produces more vesicles than any of the other tested strains. Moreover, the Slr1908-protein was also found to be important for iron uptake. Altogether, our results suggest that proteins containing the SLH/OprB-domains may have dual biological role, related to micronutrient uptake and to outer membrane stability, which, together or alone, seem to be involved in cyanobacterial vesicle biogenesis.
Highlights
Extracellular vesicles (EVs) are rich in content, as they are composed of different biomolecules, including lipids, proteins, nucleic acids, and metabolites [4,5]
Bacterial EVs have been proposed to be at the very origin of the eukaryotic endomembrane system [9]; most endosymbiotic theories postulate that eukaryotic cells must have originated from an archaeal host that engulfed an alphaproteobacterium [10]
In the particular case of green algae and plants, a better understanding of the origin, dynamics and response capacity of its cellular endomembrane system will require a deeper look into the evolutionary ancestors of chloroplasts, cyanobacteria
Summary
Extracellular vesicles (EVs) are nanosized structures (20–400 nm in diameter) presumably released by the cells of all organisms [1,2,3]. Despite their reduced size, EVs are rich in content, as they are composed of different biomolecules, including lipids, proteins, nucleic acids, and metabolites [4,5]. According to Gould et al [9], the mitochondrial ancestor naturally released EVs, which, confined within the host’s cytosol, accumulated and fused, either with each other or with the host’s plasma membrane, giving rise to the primordial endomembrane system. In the particular case of green algae and plants, a better understanding of the origin, dynamics and response capacity of its cellular endomembrane system will require a deeper look into the evolutionary ancestors of chloroplasts, cyanobacteria
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