Efficient Biostimulation of Native and Introduced Quorum-Quenching Rhodococcus erythropolis Populations Is Revealed by a Combination of Analytical Chemistry, Microbiology, and Pyrosequencing

Abstract

ABSTRACTDegradation of the quorum-sensing (QS) signals known asN-acylhomoserine lactones (AHL) by soil bacteria may be useful as a beneficial trait for protecting crops, such as potato plants, against the worldwide pathogenPectobacterium. In this work, analytical chemistry and microbial and molecular approaches were combined to explore and compare biostimulation of native and introduced AHL-degradingRhodococcus erythropolispopulations in the rhizosphere of potato plants cultivated in farm greenhouses under hydroponic conditions. We first identified gamma-heptalactone (GHL) as a novel biostimulating agent that efficiently promotes plant root colonization by AHL-degradingR. erythropolispopulation. We also characterized an AHL-degrading biocontrolR. erythropolisisolate, R138, which was introduced in the potato rhizosphere. Moreover, root colonization by AHL-degrading bacteria receiving different combinations of GHL and R138 treatments was compared by using a cultivation-based approach (percentage of AHL-degrading bacteria), pyrosequencing of PCR-amplifiedrrsloci (total bacterial community), and quantitative PCR (qPCR) of theqsdAgene, which encodes an AHL lactonase inR. erythropolis. Higher densities of the AHL-degradingR. erythropolispopulation in the rhizosphere were observed when GHL treatment was associated with biocontrol strain R138. Under this condition, the introducedR. erythropolispopulation displaced the nativeR. erythropolispopulation. Finally, chemical analyses revealed that GHL, gamma-caprolactone (GCL), and their by-products, gamma-hydroxyheptanoic acid and gamma-hydroxycaproic acid, rapidly disappeared from the rhizosphere and did not accumulate in plant tissues. This integrative study highlights biostimulation as a potential innovative approach for improving root colonization by beneficial bacteria.