Characterization and comparative analyses of type Vd-secreted phospholipases expressed in pathogenic bacteria

Abstract

Autotransporters, or type 5 secretion systems (T5SS), are widespread surface proteins of Gram-negative bacteria often associated with virulence. Three novel T5dSSs expressed in the fish pathogen Aeromonas hydrophila, the phytopathogen Ralstonia solanacearum and the human pathogen Burkholderia pseudomallei are presented in this thesis alongside the complementation of the enzymatic characterization of the T5dSS phospholipases from Pseudomonas aeruginosa and Fusobacterium nucleatum, already known to literature. Detailed information on the phospholipases’ relative enzyme activities, substrate specificities as well as the role of quaternary structure for enzyme activity and stability are shown. Furthermore, a low resolution (6 Å) structure of the T5dSS phospholipase from the fish pathogen Aeromonas hydrophila is presented, showing high structural similarity with the T5dSS present in Pseudomonas aeruginosa. Additionally, the results in the thesis show the role of the periplasmic chaperone SurA on integration of the T5dSS of Pseudomonas aeruginosa into the outer membrane as well as the chaperones effect on membrane integrity and outer membrane composition. With an increased accessibility as well as sensitivity to antibiotics resulting from a conditional deletion of SurA, the chaperone might qualify as potential novel antimicrobial target.