Photobacterium damselae subsp. piscicida responds to antimicrobial peptides through phage-shock-protein A (PspA)-related extracytoplasmic stress response system

Aims: To investigate whether Photobacterium damselae subsp. piscicida (Phdp) can sense and directly respond to the presence of cationic antimicrobial peptides (AMPs). Methods and Results: We performed proteomic methodologies to investigate the responsive proteins of Phdp on exposure to AMP Q6. Proteins significantly altered were analysed by two-dimensional gel electrophoresis (2-DE) and LC-ESI-Q-TOF MS/MS, thus resulting in five outer membrane proteins (OMPs), seven inner membrane proteins (IMPs) and 17 cytoplasmic proteins (CPs) identified. Quantitative real-time PCR was also applied to monitor the mRNA expression level of these target proteins. Conclusions: COG analysis revealed that upon exposure to AMP Q6, the majority of the upregulated proteins were involved in signal transduction mechanism, carbohydrate transport and metabolism, post-translational modification, protein turnover and chaperones, while the downregulated proteins were mainly related to energy production and conversion. Among them, phage-shock-protein A (PspA)-related stress response system was considered to play a crucial role. Significance and Impact of the Study: To the best of our knowledge, this is the first report elucidating Phdp AMP-response mechanism using proteomics approach. AMP-responsive proteins identified in this study could serve as attractive targets for developing more effective antimicrobial agents against Phdp and other marine bacterial pathogens.