Gene expression profiling of Ralstonia solanacearum in unexplored environmental niches reveals essential genes to complete its life cycle
Bacterial pathogens exhibit a remarkable ability to persist and thrive in diverse ecological niches. Understanding the mechanisms enabling their transition between environments is crucial to control dissemination and potential disease outbreaks. Here, we use Ralstonia solanacearum, the causing agent of the bacterial wilt disease, as a model to investigate the bacterial transcriptomic adaptation to two environments, water and soil, and compare it with the well-studied in planta gene expression. We identified extensive transcriptional reprogramming in response to each environment. Strikingly, gene expression in water resembled expression during late xylem colonization, with an intriguing induction of the type 3 secretion system (T3SS). We reveal that basic pH and also to nutrient scarcity - conditions also encountered in planta during late infection stages - trigger the T3SS induction. In the soil environment, R. solanacearum upregulated stress-responses and alternate carbon source metabolism genes, mostly phenylacetate metabolism and glyoxylate cycle and downregulated virulence-associated genes. Furthermore, we proved through gain- and loss-of-function that genes encoding proteins associated with oxidative stress, such as the oxidative stress regulator OxyR and the catalase KatG, are key for survival of the bacterium in soil. This work identifies essential factors necessary for R. solanacearum to complete its life cycle and provides valuable insights into the biological processes driving pathogen adaptation to unexplored environments out of their hosts. Overall design: Soil samples inoculated with R. solanacearum for 3 days at 28C. Water samples inoculated with R. solanacearum for 6 hours at 28C.