Countless bacterial species share cramped environments where competition for space and resources is fierce. Some rely on a molecular speargun to outcompete their opponents. One of them is Pseudomonas aeruginosa. It is widespread in nature but also notorious as a difficult-to-treat hospital pathogen.
Pseudomonas can live peacefully in coexistence with other microbes. But when attacked by bacteria from different species, it rapidly assembles its own nano-speargun – the so-called type VI secretion system (T6SS) – to inject its aggressor with a toxic cocktail. But the crucial question is: How can Pseudomonas strike back when it has already been hit by a deadly cocktail itself? The answer has now been uncovered by Prof. Marek Basler’s team at the Biozentrum of the University of Basel and published in “Nature Communications”.
T6SS attack triggers defense program
The deadly cocktail consists of toxic proteins that target different sites in the bacterial cell. Some of these proteins damage or destroy the protective cell membrane, while others degrade the genetic material. “These toxic proteins typically target many vital cellular processes and structures,” explains Alejandro Tejada-Arranz, first author of the study. “We discovered that Pseudomonas can resist certain toxins delivered by the T6SS.” After an attack, Pseudomonas can therefore evade the effects of the toxin and actively launch a counterattack.
Bacteria are generally immune to toxins from their close relatives. When attacked by a different species, Pseudomonas activates a general defense program that quickly initiates a variety of protective measures. “This results in a coordinated response aimed at repairing the damage or potentially trapping toxic proteins,” says Tejada-Arranz. “For example, the bacteria use a certain membrane protein that stabilizes the damaged outer membrane.” This wide range of measures protects Pseudomonas against various types of toxic proteins injected by multiple aggressors. Its ability to assert itself in bacterial communities could possibly also play a role in problematic infections.