A Bacterial Pathogen Induces Reversible Developmental Slowing by High Reactive Oxygen Species and Mitochondrial Damage in Caenorhabditis Elegans

Abstract

Host-pathogen interactions are complex by nature, and the host developmental stage increases this complexity. Development is an energetically demanding period when biomass production and cell differentiation events occur. We investigated how a developing organism copes with the additional energy-expensive burden of pathogen stress during this crucial period. We explored this question by utilizing Caenorhabditis elegans larvae as the host and the bacterium Pseudomonas aeruginosa as the pathogen. By screening 36 P. aeruginosa isolates, we found that the CF18 strain causes a severe but reversible developmental delay. CF18 slows larval development via induction of reactive oxygen species (ROS) and mitochondrial dysfunction. In response, the larvae upregulate mitophagy and antimicrobial and detoxification genes; however, mitochondrial unfolded protein response (UPRmt) is repressed. Consistent with these observations, antioxidant or iron supplementation or the removal of larvae from CF18 rescues developmental delay, mitochondrial damage, and high ROS. We examined the virulence factors of CF18 required for developmental delay via transposon mutagenesis, RNA-sequencing, and candidate gene deletion approaches. Our results showed that virulence factors regulated by quorum sensing and the GacA/S system were responsible for developmental slowing. We also demonstrated that well-studied mitochondrial toxins of P. aeruginosa, phenazines and hydrogen cyanide, are not required for CF18-induced developmental slowing. This study highlights the importance of ROS levels and mitochondrial health as determinants of developmental rate and how pathogens can attack these important features.