No fitness cost entailed by type VI secretion system synthesis, assembly, contraction, or disassembly in enteroaggregative .

Bacteria use weapons to deliver effectors into target cells. One of these weapons, the type VI secretion system (T6SS), assembles a contractile tail acting as a spring to propel a toxin-loaded needle. Due to its size and mechanism of action, the T6SS was intuitively thought to be energetically costly.