Global responses of Aliivibrio salmonicida to hydrogen peroxide as revealed by microarray analysis

Aliivibrio salmonicida causes "cold-water vibriosis" (or "Hitra disease") in fish, including marine-reared Atlantic salmon. During development of the disease the bacterium will encounter macrophages with antibacterial activities such as production of damaging reactive oxygen species (ROS). To defend itself the bacterium will presumably start producing detoxifying enzymes, reducing agents, and proteins involved in DNA and protein repair systems. Even though responses to oxidative stress are well studied for a few model bacteria, little work has been done in general to explain how important groups of pathogens, like members of the Vibrionaceae family, can survive at high levels of ROS. We have used bioinformatic tools and microarray to study how A. salmonicida responds to hydrogen peroxide (H(2)O(2)). First, we used the recently published genome sequence to predict potential binding sites for OxyR (H(2)O(2) response regulator). The computer-based search identified OxyR sites associated with 20 single genes and 8 operons, and these predictions were compared to experimental data from Northern blot analysis and microarray analysis. In general, OxyR binding site predictions and experimental results are in agreement. Up- and down regulated genes are distributed among all functional gene categories, but a striking number of ≥2 fold up regulated genes encode proteins involved in detoxification and DNA repair, are part of reduction systems, or are involved in carbon metabolism and regeneration of NADPH. Our predictions and -omics data corroborates well with findings from other model bacteria, but also suggest species-specific gene regulation.