The role of the antimicrobial compound 2,4-diacetylphloroglucinol in the impact of biocontrol Pseudomonas fluorescens F113 on Azospirillum brasilense phytostimulators

Abstract

Pseudomonads producing the antimicrobial metabolite 2,4-diacetylphloroglucinol (Phl) can control soil-borne phytopathogens, but their impact on other plant-beneficial bacteria remains poorly documented. Here, the effects of synthetic Phl and Phl+ Pseudomonas fluorescens F113 on Azospirillum brasilense phytostimulators were investigated. Most A. brasilense strains were moderately sensitive to Phl. In vitro, Phl induced accumulation of carotenoids and poly-β-hydroxybutyrate-like granules, cytoplasmic membrane damage and growth inhibition in A. brasilense Cd. Experiments with P. fluorescens F113 and a Phl− mutant indicated that Phl production ability contributed to in vitro growth inhibition of A. brasilense Cd and Sp245. Under gnotobiotic conditions, each of the three strains, P. fluorescens F113 and A. brasilense Cd and Sp245, stimulated wheat growth. Co-inoculation of A. brasilense Sp245 and Pseudomonas resulted in the same level of phytostimulation as in single inoculations, whereas it abolished phytostimulation when A. brasilense Cd was used. Pseudomonas Phl production ability resulted in lower Azospirillum cell numbers per root system (based on colony counts) and restricted microscale root colonization of neighbouring Azospirillum cells (based on confocal microscopy), regardless of the A. brasilense strain used. Therefore, this work establishes that Phl+ pseudomonads have the potential to interfere with A. brasilense phytostimulators on roots and with their plant growth promotion capacity.

A phytobeneficial strainPlanomicrobiumsp. MSSA-10 triggered oxidative stress responsive mechanisms and regulated the growth of pea plants under induced saline environment

“…; Couillerot et al . ). Hence, it seems that MSSA‐10 rif modulated the structure as well as physiology of roots, enhancing their ability of water and nutrient uptake.…”

Analysis of genes contributing to plant-beneficial functions in plant growth-promoting rhizobacteria and related Proteobacteria

“…Mutational inactivation of a particular PBFC gene may reduce (without necessarily abolishing) plant-beneficial effects in PGPR strains137, and genetic acquisition of an additional PBFC gene has the potential to enhance PGPR performance839. This indicates that possessing multiple PBFC genes should confer a better efficiency at enhancing plant growth.…”

Plant growth-promoting rhizobacteria and root system functioning

“…DAPG is a well-known antimicrobial compound produced by biocontrol fluorescent pseudomonads (Couillerot et al, 2009). At lower concentrations, DAPG can also be a signal molecule for plants, inducing systemic resistance (Iavicoli et al, 2003; Bakker et al, 2007), stimulating root exudation (Phillips et al, 2004), and enhancing root branching (Brazelton et al, 2008; Couillerot et al, 2011; Walker et al, 2011). DAPG can interfere with an auxin-dependent signaling pathway and thus modify RSA (Brazelton et al, 2008).…”

“…Interactions will take place within a functional group, as illustrated above with QS regulation of phenazine production in fluorescent Pseudomonas PGPR (Pierson et al, 1994). Interactions may also take place between different PGPR functional groups ( Figure 3 ), integrating competitive and inhibitory effects (Couillerot et al, 2011), signal jamming (Boyer and Wisniewski-Dyé, 2009) and positive signaling (Combes-Meynet et al, 2011), as well as more indirect processes such as root exudation modifications (Phillips et al, 2004; Dardanelli et al, 2010). These interactions have the potential to modulate spatial colonization patterns of PGPR on roots (Couillerot et al, 2011) and to affect PGPR performance (Pierson et al, 1998).…”