Cell density-dependent gene contributes to efficient seed colonization by Pseudomonas putida KT2440.
We have characterized the expression pattern of a gene, ddcA, involved in initial colonization of corn seeds by Pseudomonas putida KT2440. The ddcA gene codes for a putative membrane polypeptide belonging to a family of conserved proteins of unknown function. Members of this family are widespread among prokaryotes and include the products of a Salmonella enterica serovar Typhimurium gene expressed during invasion of macrophages and psiE, an Escherichia coli phosphate starvation-inducible gene. Although its specific role is undetermined, the presence of ddcA in multicopy restored the seed adhesion capacity of a KT2440 ddcA mutant. Expression of ddcA is growth phase regulated, being maximal at the beginning of stationary phase. It is independent of RpoS, nutrient depletion, or phosphate starvation, and it is not the result of changes in the medium pH during growth. Expression of ddcA is directly dependent on cell density, being also stimulated by the addition of conditioned medium and of seed exudates. This is the first evidence suggesting the existence of a quorum-sensing system in P. putida KT2440. The potential implication of such a signaling process in seed adhesion and colonization by the bacterium is discussed.
Espinosa-Urgel
Manuel
M
Department of Plant Biochemistry and Molecular and Cellular Biology, Estacíon Experimental del Zaidín, CSIC, Granada 18008, Spain. manuel.espinosa@eez.csic.es
Ramos
Juan-Luis
JL
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D017931:DNA Primers; D005798:Genes, Bacterial / Q000235:genetics; D007700:Kinetics; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016958:Pseudomonas putida / Q000235:genetics* / Q000254:growth & development*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D017931:DNA Primers