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. 2019 Dec 24;8(1):42.
doi: 10.3390/microorganisms8010042.

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

Clara Vega  1   2 , Miguel Rodríguez  1   2 , Inmaculada Llamas  1   2 , Victoria Béjar  1   2 , Inmaculada Sampedro  1   2
Affiliations
Free PMC article

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

Clara Vega et al. Microorganisms. .
Free PMC article

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.

Keywords: PGPR; Staphylococcus equorum strain EN21; bacterial phytopathogen; communication silencing; halotolerant bacterium; quorum quenching; quorum sensing.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Quorum quenching (QQ) activity of strain EN21 against crude N-acyl homoserine lactone (AHL) extracts from A. fabrum and P. syringae. pv. tomato.
Figure 2
Figure 2
Effect of EN21 AHL-degrading activity against bacterial plant pathogens in potato tuber, carrot and pear assays. Tissues were inoculated with sterile water (control), EN21 and phytopathogen mono-cultures and phytopathogen-EN21 co-cultures (from left to right in panel).
Figure 3
Figure 3
Visualization of tissue structure and chlorophyll content in Arabidopsis leaves by differential interference contrast (DIC) and epifluorescence microscopy 100× (first and second row, respectively). Leaves were inoculated with sterile water (control), EN21 and phytopathogen mono-cultures and phytopathogen-EN21 co-culture (from left to right in panel). Micrographs from each row were taken under the same exposure time, gamma and gain values for comparative analysis. Epifluorescence images were digitally coloured.
Figure 4
Figure 4
Percentage of living, dead, necrotic and chlorotic tomato leaves. Leaves were inoculated with sterile water (control), EN21 and phytopathogen mono-cultures and phytopathogen-EN21 co-culture.
Figure 5
Figure 5
Tomato plants sprayed with sterile water (control), EN21, P. syringae pv. tomato and P. syringae pv. tomato + EN21 (B). Disease symptoms were inspected and photographed three days after infection (A). Necrotic (1A) and clorotic (2A) symptoms were observed.
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