Mutation of the Carboxy-Terminal Processing Protease in Acinetobacter baumannii Affects Motility, Leads to Loss of Membrane Integrity, and Reduces Virulence

Motility plays an essential role in the host-parasite relationship of pathogenic bacteria, and is often associated with virulence. While many pathogenic bacteria use flagella for locomotion, strains do not have flagella, but have other features that aid in their motility. To study the genes involved in motility, transposon mutagenesis was performed to construct mutant strains. Mutant strain MR14 was found to have reduced motility, compared to wild-type ATCC 17978. NCBI BLAST analysis revealed that the Tn transposon in the MR14 genome is integrated into the gene that encodes for carboxy-terminal processing protease (Ctp). Additionally, MR14 exhibits a mucoidy, sticky phenotype as the result of increased extracellular DNA (eDNA) caused by bacterial autolysis. Transmission and scanning electron microscopy revealed cytoplasmic content leaving the cell and multiple cell membrane depressions, respectively. MR14 showed higher sensitivity to environmental stressors. Mutation of the gene reduced invasion and adhesion of to airway epithelial cells, potentially due to increased hydrophobicity. In the zebrafish model of infection, MR14 increased the survival rate by 40% compared to the wild-type. Taken together, the gene in has a pivotal role in maintaining membrane integrity, adaptation to environmental stress, and controlling virulence.