Capsular polysaccharide restrains type VI secretion in Acinetobacter baumannii

Area of Science:

• Microbiology
• Bacterial cell-surface structures
• Bacterial secretion systems

Background:

• The type VI secretion system (T6SS) is crucial for interbacterial competition, requiring membrane penetration.
• Cell envelope structures like capsular polysaccharides (CPS) can impede T6SS function due to steric hindrance.

Purpose of the Study:

• To investigate the impact of Acinetobacter baumannii's CPS on T6SS antibacterial activity.
• To understand how CPS influences the bacterium's own T6SS efficacy and protein regulation.

Main Methods:

• Analysis of T6SS-mediated bacterial killing assays with varying CPS levels.
• Assessment of T6SS inner tube protein Hcp levels under different conditions.
• Investigation of protein degradation pathways involving the ClpXP protease.

Main Results:

• Acinetobacter baumannii CPS provides resistance against T6SS attacks from other bacteria.
• Surface-bound CPS reduces the efficacy of the bacterium's own T6SS under normal growth.
• CPS overproduction, induced by genetic modification or antibiotics, exacerbates T6SS impairment.
• Acinetobacter baumannii regulates Hcp protein levels via ClpXP-mediated degradation to match secretion capacity.

Conclusions:

• A complex interplay exists between T6SS and CPS in Acinetobacter baumannii.
• CPS acts as a double-edged sword, offering defense while compromising self-attack capabilities.
• The bacterium employs regulatory mechanisms, including protease-mediated degradation, to adapt T6SS function to environmental cues and capsule levels.