Identification & Characterization of New Pseudomonas aeruginosa Type III Secretion System Effectors

Pseudomonas aeruginosa is a non-fermentative, Gram-negative rod that lives in a variety of environments and hosts. In humans, P. aeruginosa is one of the leading opportunistic pathogens in nosocomial infections. P. aeruginosa harbors a Type III secretion system (T3SS), which is found to enhance disease severity. T3SS delivers effectors from the cytosol of the bacteria into the cytosol of the host in a highly regulated manner. P. aeruginosa has four well characterized T3SS effectors: ExoS, ExoT, ExoU, and ExoY. This is a surprising low number of known effectors considering the vast range of hosts and environments the bacterium is associated with. Recently four additional effectors: PemA, PemB, PemC, and PemD, were identified by our group using a machine learning approach. In this study, a list of 55 potential T3SS candidate effectors were created and 16 of them were tested using in vitro and in vivo assays to test a T3SS-dependent secretion. Two of the proteins (PA39016_001140016 – PemE and PA14_59110 - PemF), showed the typical T3SS secretion phenotype. Finally, in order to examine the new effectors potential contribution to the virulence of P. aeruginosa, characterization assays were performed in human cell line, yeast and C. elegans. We were able to show, that although PemE and PemF do not effect C. elegans`s lifespan; C. elegans that were infected by a P. aeruginosa strain overexpressing PemB, showed significant shorter lifespan compared to the control strain. Taken together, these results highlight the functionality of additional novel T3SS effectors to the virulence and fitness of P. aeruginosa.