EXPOSURE TO OXIDATIVE STRESS INDUCES EXTRACELLULAR POLYSACCHARIDE PRODUCTION IN BURKHOLDERIA THAILANDENSIS BIOFILM

Background Biofilm formation is a common strategy among bacteria to survive in soil and aquatic environments, as well as an effective mechanism for pathogens to persist within the host. Pathogens can be exposed to oxidative stress during host colonization, e.g. in presence of macrophages or antibiotics, and they can react switching to a biofilm lifestyle, where cells might be less sensitive to external stresses. However, the connection between biofilm formation and cellular response to oxidative stress remains to be investigated. Objectives Burkholderia thailandensis is a model organism of B.pseudomallei, the etiologic agent of melioidosis, a serious disease endemic in South-East Asia and Northern Australia, whose pathogenesis is still poorly understood. We investigated the response to oxidative stress in a B. thailandensis biofilm in order to evaluate its adaptation strategies. Methods We set up a protocol for the formation of a colony biofilm, and monitored the levels of intracellular and extracellular oxidative stress, either endogenous or exogenous, during the biofilm growth. We evaluated the effects of oxidative stress defining the exopolymeric substances composition and the levels of catalase activity. Conclusions Monitoring of reactive oxygen species (ROS) revealed that the early stages of biofilm formation are characterized by strong induction of oxidative stress, which decreases as the biofilm reached the mature phase. Surprisingly, exposure to exogenous oxidative stress only led to low generation of ROS; however, it affected biofilm morphology and triggered the production of a polysaccharide-rich matrix, thus confirming the role of polysaccharides in protection from oxidative stress.