Characterization of the SPI-1 and Rsp type three secretion systems in Pseudomonas fluorescens F113

Pseudomonas fluorescens F113 is a plant growthpromoting
rhizobacterium (PGPR) isolated from the
sugar beet rhizosphere. The recent annotation of the
F113 genome sequence has revealed that this strain
encodes a wide array of secretion systems, including
two complete type three secretion systems (T3SSs)
belonging to the Hrp1 and SPI-1 families. While Hrp1
T3SSs are frequently encoded in other P. fluorescens
strains, the presence of a SPI-1 T3SS in a plantbeneficial
bacterial strain was unexpected. In this
work, the genetic organization and expression of
these two T3SS loci have been analysed by a combination
of transcriptional reporter fusions and
transcriptome analyses. Overexpression of two transcriptional
activators has shown a number of genes
encoding putative T3 effectors. In addition, the influence
of these two T3SSs during the interaction of
P. fluorescens F113 with some bacterial predators
was also assessed. Our data revealed that the transcriptional
activator hilA is induced by amoeba and
that the SPI-1 T3SS could potentially be involved in
resistance to amoeboid grazing.