Inactivation of gacS Does Not Affect the Competitiveness of Pseudomonas chlororaphis in the Arabidopsis thaliana Rhizosphere

AUTOR(ES)

Schmidt-Eisenlohr, Heike

FONTE

American Society for Microbiology

RESUMO

Quorum-sensing-controlled processes are considered to be important for the competitiveness of microorganisms in the rhizosphere. They affect cell-cell communication, biofilm formation, and antibiotic production, and the GacS-GacA two-component system plays a role as a key regulator. In spite of the importance of this system for the regulation of various processes, strains with a Gac− phenotype are readily recovered from natural habitats. To analyze the influence of quorum sensing and the influence of the production of the antibiotic phenazine-1-carboxamide on rhizosphere colonization by Pseudomonas chlororaphis, a gnotobiotic system based on Arabidopsis thaliana seedlings in soil was investigated. Transposon insertion mutants of P. chlororaphis isolate SPR044 carrying insertions in different genes required for the production of N-acyl-homoserine lactones and phenazine-1-carboxamide were generated. Analysis of solitary rhizosphere colonization revealed that after prolonged growth, the population of the wild type was significantly larger than that of the homoserine lactone-negative gacS mutant and that of a phenazine-1-carboxamide-overproducing strain. In cocultivation experiments, however, the population size of the gacS mutant was similar to that of the wild type after extended growth in the rhizosphere. A detailed analysis of growth kinetics was performed to explain this phenomenon. After cells grown to the stationary phase were transferred to fresh medium, the gacS mutant had a reduced lag phase, and production of the stationary-phase-specific sigma factor RpoS was strongly reduced. This may provide a relative competitive advantage in cocultures with other bacteria, because it permits faster reinitiation of growth after a change to nutrient-rich conditions. In addition, delayed entry into the stationary phase may allow more efficient nutrient utilization. Thus, GacS-GacA-regulated processes are not absolutely required for efficient rhizosphere colonization in populations containing the wild type and Gac− mutants.

Documentos Relacionados

• The Competitiveness of Pseudomonas chlororaphis Carrying pJP4 Is Reduced in the Arabidopsis thaliana Rhizosphere
• Genetic Evidence that Loss of Virulence Associated with gacS or gacA Mutations in Pseudomonas syringae B728a Does Not Result from Effects on Alginate Production
• Swarming by Pseudomonas syringae B728a Requires gacS (lemA) and gacA but Not the Acyl-Homoserine Lactone Biosynthetic Gene ahlI
• The Two-Component Regulators GacS and GacA Influence Accumulation of the Stationary-Phase Sigma Factor ςS and the Stress Response in Pseudomonas fluorescens Pf-5
• Molecular Nature of Spontaneous Modifications in gacS Which Cause Colony Phase Variation in Pseudomonas sp. Strain PCL1171