Staphylococcus aureus Alpha-Toxin Induces the Formation of Dynamic Tubules Labeled with LC3 within Host Cells in a Rab7 and Rab1b-Dependent Manner

María M. López de Armentia, María C. Gauron, María I. Colombo

Staphylococcus aureus is a pathogen that causes severe infectious diseases that eventually lead to septic and toxic shock. S. aureus infection is characterized by the production of virulence factors, including enzymes and toxins. After internalization S. aureus resides in a phagosome labeled with Rab7 protein. Here, we show that S. aureus generates tubular structures marked with the small GTPases Rab1b and Rab7 and by the autophagic protein LC3 at early times post-infection. As shown by live cell imaging these tubular structures are highly dynamic, extend, branch and grow in length. We have named them S. aureus induced filaments (Saf). Furthermore, we demonstrate that the formation of these filaments depends on the integrity of microtubules and the activity of the motor protein Kinesin-1 (Kif5B) and the Rab-interacting lysosomal protein (RILP). Our group has previously reported that α-hemolysin, a secreted toxin of S. aureus, is responsible of the activation of the autophagic pathway induced by the bacteria. In the present report, we demonstrate that the autophagic protein LC3 is recruited to the membrane of S. aureus induced filaments and that α-hemolysin is the toxin that induces Saf formation. Interestingly, increasing the levels of intracellular cAMP significantly inhibited Saf biogenesis. Remarkably in this report we show the formation of tubular structures that emerge from the S. aureus-containing phagosome and that these tubules generation seems to be required for efficient bacteria replication.