Cellular effects of outer membrane vesicles isolated from pks-positive strains of bacteria

The pks island is a gene cluster harbored by certain strains of gram-negative bacteria, that encodes the production of the genotoxic compound colibactin. Despite the importance of colibactin as an inducer of DNA damage, little is known about how it is transported into the affected cells. Here we explore the possible involvement of outer membrane vesicles (OMVs) in colibactin toxicity. We exposed HeLa cells to OMVs from NC101 ( pks ⁺ ) and from the NC101 ΔclbP deletion mutant lacking the capacity to make mature colibactin. Some megalocytosis (~ 40% increase in nucleus size) was observed as a response to OMVs from NC101 after 72 hours. The OMVs from both wild-type NC101 and ΔclbP mutant were sufficient to cause a decrease in the number of viable cells after 4 and 72 hours. Additional effects include the activation of the DNA repair machinery. Images obtained through high-resolution confocal microscopy also reveal that labeled OMVs from all strains can enter the cell and locate inside the nucleus, causing a more pronounced enlargement vs. cells with no OMVs. In all, the damage caused by the isolated OMVs recapitulates some of the typical phenotypes associated with pks ⁺ E. coli , although not all the effects were found to be pks -specific.