Pseudomonas in the underworld:: The secret life of Pseudomonas fluorescens SBW25

Pseudomonas fluorescens SBW25 is a gram-negative, fluorescent pseudomonad that is able to colonise the roots and leaves of a wide range of plants. PfSBW25 has been widely adopted as a model organism for investigations into the molecular basis of plant colonisation, plant growth promotion and biocontrol, and is also used as a model organism in studies of biofilm formation and experimental evolution. The 6.7 Mb genome of PfSBW25 is currently being sequenced at the Sanger Institute. We have developed two in vivo expression technology (IVET) systems for P. fluorescens SBW25, and have used IVET as a functional genomics approach to identify and characterise more than a hundred plant-induced genes from P. fluorescens SBW25. The predicted functions of many of these genes can be assigned to broad functional categories such as nutrient acquisition, surface colonisation, stress tolerance, antibiotic biosynthesis, protein secretion and transcriptional regulation. We have begun the process of analysing the function and expression of some of these plant-induced genes in depth, focusing in particular on genes encoding a rhizosphere-induced type III protein secretion system (TTSS) that is similar to the Hrp TTSS of P. syringae. Functional genomic analyses of P. fluorescens SBW25 have provided insight into the biology and ecology of plant-colonising Pseudomonas, and into the utility and limitations of functional genomic techniques in understanding the biology of bacteria in complex environments.