Silencing of Phytopathogen Communication by the Halotolerant PGPR Staphylococcus Equorum Strain EN21

Abstract

Increasing world food demand together with soil erosion and indiscriminate use of chemical fertilization highlight the need to adopt sustainable crop production strategies. In this context, a combination of plant growth-promoting rhizobacteria (PGPR) and pathogen management represents a sustainable and efficient alternative. Though little studied, halophilic and halotolerant PGPR could be a beneficial plant growth promotion strategy for saline and non-saline soils. The virulence of many bacterial phytopathogens is regulated by quorum sensing (QS) systems. Quorum quenching (QQ) involves the enzymatic degradation of phytopathogen-generated signal molecules, mainly N-acyl homoserine lactones (AHLs). In this study, we investigate plant growth-promoting (PGP) activity and the capacity of the halotolerant bacterium Staphylococcus equorum strain EN21 to attenuate phytopathogens virulence through QQ. We used biopriming and in vivo tomato plant experiments to analyse the PGP activity of strain EN21. AHL inactivation was observed to reduce Pseudomonas syringae pv. tomato infections in tomato and Arabidopsis plants. Our study of Dickeya solani, Pectobacterium carotovorum subsp. carotovorum and Erwinia amylovora bacteria in potato tubers, carrots and pears, respectively, also demonstrated the effectiveness of QS interruption by EN21. Overall, this study highlights the potential of strain S. equorum EN21 in plant growth promotion and QQ-driven bacterial phytopathogen biocontrol.Microorganisms 2020, 8, 42 2 of 17 mechanisms are involved in producing enzymes such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, auxins, exopolysaccharides and siderophores, play an important role in boosting plant growth under stress conditions including salinity [4].The virulence and associated functions of many bacterial phytopathogens, which cause major economic losses, are regulated by quorum sensing (QS) systems. One promising strategy, involving quorum quenching (QQ), to combat infections is based on the enzymatic degradation of signal molecules [5]. QS is used by a wide variety of bacteria to regulate gene expression in a cell density-dependent manner [6][7][8]. This mechanism involves the production, release and recognition of the accumulation of signalling molecules known as autoinducers [9]. The best-studied autoinducers are N-acyl homoserine lactones (AHLs) which are produced by many Proteobacteria. Diffusible signal factors (DSFs) and quinolones, which have been identified in Pseudomonas aeruginosa [10] and Xanthomonas spp. [11], are also autoinducers. QS plays an important role in the regulation of bacterial functions including virulence gene expression, biofilm formation and antibiotic resistance [6,[12][13][14][15]. In plant pathogenic bacteria such as Pseudomonas syringae pv. syringae [12], Pectobacterium carotovorum [16] and Agrobacterium tumefaciens [17], QS has been reported to regulate cell wall-degrading enzyme production, cellular motility and biofilm formation. Given the contribution of these QS-coordinated virulen...

Quorum Sensing Regulation in Phytopathogenic Bacteria

“…In addition, the results obtained by the biopriming of seeds showed PGPR producing degradative enzymes of QS signal molecules. These QQ strategies are promising [ 112 , 113 ]. A new VFM QS system has also been identified, highlighting the need to screen QQ mechanisms interfering with this QS system.…”

Beneficial microbes in agriculture under abiotic stress conditions: An overview

“…In addition, soil bacteria also gave transgenic pea a positive relationship and increased tolerance for salt stress (Ali et al, 2015) [6] . (Vega et al, 2020) [92] stated that inoculation of crops with natural halotolerant PGPR strains like S. equorum strain EN21, with its high quorum quenching ability, could be an effective biocontrol strategy for both saline and non-saline soils. Another strain P. geniculate MF-84 decreases Na+ uptake and increases K+ and Ca2 + uptake in maize roots suggesting MF-84's function in maintaining ionic balance / homeostasis in plant roots under higher salt conditions.…”

Bacterial Plant Biostimulants: A Sustainable Way Towards Improving Growth, Productivity, and Health of Crops

“…In a recent study, a halotolerant plant growth-promoting bacterium, Staphylococcus equorum EN21 triggered ISR against Pseudomonas syringae (pv. Tomato) through quorum quenching of acylhomoserine in Arabidopsis and tomato plants[174]. ISR activity of the elicitor, oxo-C14-HSL was observed in tomato and wheat against Phytophthora infestans and Puccinia graminis f., respectively[175].…”