Extracellular vesicle proteomes reflect developmental phases of Bacillus subtilis

摘要

Background: Extracellular vesicles (EV) are spherical membrane-bound vesicles with nano-scale diameters, which are shed to the extracellular region by most eukaryotic and prokaryotic cells. Bacterial EV are proposed to contribute to intercellular communication, bacterial survival and human pathogenesis as a novel secretion system. EV have been characterized from many Gram-negative species and, more recently, from several vegetative Gram-positive bacteria. Further characterization of EVand their molecular cargos will contribute to understanding bacterial physiology and to developing therapeutic approaches. Results: Bacillus subtilis were observed to release EVto a similar extent during sporulation as during the vegetative growth phase. However, the two vesicular cargos show qualitatively and quantitatively different proteomes. Among 193 total proteins identified across both samples, 61 were shown to be significantly more abundant in EV shed by sporulating cells, with (log) ratio of spectral counts Rsc > 1 and Fisher-exact test FDR < 5 %. Sixty-two proteins were found to be significantly more abundant in EVshed by vegetative cells. Membrane fusion was shown to take place between these EVs and Gram-positive cells. Conclusion: Biogenesis of EVisa continuous process over the entire life cycle of this sporulating bacterium. The formation of EV during sporulation is strongly supported by the delineation of protein content that differs from the proteome of EV formed by vegetative spores. Extracellular vesicles (EV) are universally produced from diverse eukaryotes and prokaryotes [1, 2]. They are spherical and membranous vesicles shed to the extracellular region, and enclosed by a lipid bilayer with a nano-scale diameter between 20 and 1000 nm depending on the organism [3, 4]. As in the case with EV shed by multicellular organisms, Gram-negative bacterial EV carry diverse cell-derived components, including numerous proteins, lipids, genetic materials, toxins, communication signals, and immunomodulatory compounds [4-6]. EV have been proposed to contribute to intercellular communication, bacterial survival, and human pathogenesis as a novel secretion system [1, 4-6]. Initially, Gram-positive bacteria were thought not to produce EV because they lack outer membranes. However, Gram-positive bacterial EV were microscopically observed in 1990 [7], and now EV have been characterized from several infectious Gram-positive bacteria, including S. aureus [8], B. anthracis [9], Listeria monocytogenes [10], Bacillus subtilis [11], and Clostridium perfringens [12].