AsianScientist (Apr. 19, 2016) – A recent study by an international team of researchers has identified a phenomenon called explosive cell lysis as crucial to the production of membrane vesicles and biofilm formation, two processes that are key to how bacteria form and attack healthy cells. The study was published in Nature Communications.
Membrane vesicles are tiny spheres that develop from bacterial membranes and contain a mixture of proteins, DNA, and RNA. They are important to bacteria’s ability to cause disease as they play vital roles in invasion, secretion, and signaling.
They also contribute to the formation of biofilms, the slimy three-dimensional structures that form when bacteria adhere to moist surfaces such as teeth or wounds. Extracellular DNA (eDNA) is key to the structural organization of biofilms, yet it was not previously known how certain structural proteins or eDNA are released.
To answer this question, the researchers used live cell microscopy of the pathogenic bacterium Pseudomonas aeruginosa to reveal that bacterial cells quickly changed from rod- to round-shaped, and then explode.
“Cells lose their structural integrity in 5-10 seconds, and the explosion releases cellular content including eDNA, proteins, and membrane fragments into the surrounding environment,” corresponding author Associate Professor Cynthia Whitchurch of the University of Technology Sydney explained.
Using super-resolution microscopy to follow the explosions, they found a surprising observation. The membrane fragments produced by exploding bacteria curled up to form membrane vesicles that captured eDNA and other cellular components released by the explosion.
“This was completely unexpected, as until now, bacterial membrane vesicles were thought to form from membranous protrusions at the cell surface,” explained co-corresponding and co-first author Masanori Toyofuku, an assistant professor at the University of Tsukuba.
The team found that the explosions are caused by an enzyme (Lys) used by bacteria-infecting viruses (phages) and phage-like elements to disrupt the cell wall of their hosts. Using a mutant bacterial strain incapable of producing Lys, they discovered that the enzyme was needed to produce eDNA and membrane vesicles.
Through a range of experiments, the team also demonstrated that exposure of cells to different forms of stress, such as antibiotics or DNA damaging agents, stimulated expression of the gene encoding Lys and induced explosive cell lysis.
This shows that the bacterial ‘SOS’ response triggers explosive cell lysis in response to unfavorable environmental conditions, according to the researchers. This mechanism may enable bacteria to release important cellular factors for use by bacterial communities as public goods, and knowledge of its control could be used to interfere with biofilm formation of pathogenic bacteria.
The article can be found at: Turnbull et al (2016) Explosive Cell Lysis as a Mechanism for the Biogenesis of Bacterial Membrane Vesicles and Biofilms.
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Source: University of Tsukuba.
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