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Cryo-electron tomography analysis of membrane vesicles from Acinetobacter baumannii ATCC19606 T
Roman I Koning1, Anna de Breij, Gert T Oostergetel
1Department of Molecular Cell Biology, Section Electron Microscopy, Einthovenweg 20, P.O. Box 9600, 2300 RC, Leiden University Medical Center, The Netherlands. r.i.koning@lumc.nl
Abstract:
Acinetobacter baumannii is an important nosocomial pathogen responsible for colonization and infection of critically ill patients. Its virulence attributes together with the condition of the host determine the pathogenicity of A. baumannii. These virulence factors may be delivered to host cells by membrane vesicles. The aim of this study was to characterize the formation and morphology of membrane vesicles (MVs) from A. baumannii ATCC19606(T) using cryo-electron microscopy. Cryo-electron microscopy imaging of A. baumannii in broth cultures revealed the formation of small (≈ 30 nm) outer membrane vesicles at distal ends of early log-phase bacteria and larger (200-500 nm) membrane vesicles at septa of dividing bacteria. In the stationary phase vesicles comprising both inner and outer membranes were observed. In addition, we noted the presence of highly branched membrane structures originating from bacterial remnants forming large numbers of vesicles that were covered with proteins. Exposure of A. baumannii to sub-inhibitory concentrations of the antibiotic ceftazidime resulted in an increase in formation of MVs. Together, our results revealed multiple ways of vesicle formation leading to morphologically different MVs in the various stages of in vitro bacterial cultures.
Insights
Acinetobacter baumannii forms diverse membrane vesicles (MVs) during different growth stages. Antibiotic stress increases MV production, potentially impacting virulence.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Cell Biology
Background:
- Acinetobacter baumannii is a significant nosocomial pathogen.
- Bacterial virulence factors can be delivered via membrane vesicles (MVs).
- Understanding MV formation is crucial for A. baumannii pathogenicity.
Purpose of the Study:
- To characterize the formation and morphology of MVs from A. baumannii ATCC19606(T).
- To investigate the impact of growth phase and antibiotic stress on MV production.
Main Methods:
- Cryo-electron microscopy (cryo-EM) was used to image A. baumannii.
- Bacteria were cultured in vitro under different conditions (growth phases, sub-inhibitory antibiotic concentrations).
Main Results:
- Distinct MV populations were observed: small outer membrane vesicles (≈30 nm) from log-phase bacteria, larger vesicles (200-500 nm) from dividing bacteria, and mixed inner/outer membrane vesicles in stationary phase.
- Bacterial remnants formed branched structures yielding protein-covered vesicles.
- Sub-inhibitory ceftazidime treatment increased MV formation.
Conclusions:
- Acinetobacter baumannii exhibits multiple mechanisms for MV biogenesis, producing morphologically diverse vesicles.
- Vesicle formation is dynamic and influenced by bacterial growth stage and environmental stress, such as antibiotic exposure.
