Alginate genes are required for optimal soil colonization and persistence by Pseudomonas fluorescens Pf0-1

Pseudomonas fluorescens strains are important candidates for use as biological control agents to reduce fungal diseases on crop plants. To understand the ecological success of these bacteria and for successful and stable biological control, determination of how these bacteria colonize and persist in soil environments is critical. Here we show that P. fluorescens Pf0-1 is negatively impacted by reduced water availability in soil, but adapts and persists. A pilot transcriptomic study of Pf0-1 colonizing moist and dehydrated soil was used to identify candidate genetic loci, which could play a role in the adaptation to dehydration. Genes predicted to specify alginate production were identified and chosen for functional evaluation. Using deletion mutants, predicted alginate biosynthesis genes were shown to be important for optimal colonization of moist soil, and necessary for adaptation to reduced water availability in dried soil. Our findings extend in vitro studies of water stress into a more natural system and suggest alginate may be an essential extracellular product for the lifestyle of P. fluorescens when growing in soil.