Quorum Quenching Activity of the PGPR Bacillus subtilis UD1022 Alters Nodulation Efficiency of Sinorhizobium meliloti on Medicago truncatula

Abstract

Plant growth-promoting rhizobacteria (PGPR) have enormous potential for solving some of the myriad challenges facing our global agricultural system. Intense research efforts are rapidly moving the field forward and illuminating the wide diversity of bacteria and their plant beneficial activities. In the development of better crop solutions using these PGPR, producers are including multiple different species of PGPR in their formulations in a “consortia” approach. While the intention is to emulate more natural rhizomicrobiome systems, the aspect of bacterial interactions has not been properly regarded. By using a tri-trophic model of Medicago truncatula A17 Jemalong, its nitrogen (N)-fixing symbiont Sinorhizobium meliloti Rm8530, and the PGPR Bacillus subtilis UD1022, we demonstrate indirect influences between the bacteria affecting their plant growth-promoting activities. Co-cultures of UD1022 with Rm8530 significantly reduced Rm8530 biofilm formation and downregulated quorum sensing (QS) genes responsible for symbiotically active biofilm production. This work also identifies the presence and activity of a quorum quenching lactonase in UD1022 and proposes this as the mechanism for non-synergistic activity of this model “consortium.” These interspecies interactions may be common in the rhizosphere and are critical to understand as we seek to develop new sustainable solutions in agriculture.

Insights into Adaptive Mechanisms of Extreme Acidophiles Based on Quorum Sensing/Quenching-Related Proteins

“…It is common that AHL synthases are able to produce more than one kind of AHL. The SinI of Sinorhizobium meliloti synthesizes five different forms of AHLs, ranging from C 12 -AHL to C 18 -AHL, including some oxo-AHLs and a monounsaturated AHL ( 43 ). Longer-chain AHLs seem to be more insulated from chemical degradation and utilized by microorganisms in harsher environments, suggesting that cross talk might emerge between A. ferrooxidans and other bacterial species inhabiting the bioleaching ecological niche ( 44 ).…”

Multiple Metabolic Phenotypes as Screening Criteria Are Correlated With the Plant Growth-Promoting Ability of Rhizobacterial Isolates

“…The diversity of PGP mechanisms means that multiple plant agronomic parameters may change due to the action of PGPR. So, the standards for evaluating the performance of PGPR should include not only plant growth traits, such as shoot elongation, plant height, plant biomass, and yield ( Tabassum et al, 2017 ; Rosier et al, 2021 ), but also more targeted indicators, such as root architecture, flowering time, and plant enzyme activity, in some specific cases ( Chaney and Baucomn, 2020 ; Chu et al, 2020 ; Lee et al, 2020 ; Mahdavi et al, 2020 ). In addition, a variety of comprehensive indexes calculated based on several plant parameters have previously been used as the main standard to evaluate the quality of fruit, plant vigor, and physiological parameters.…”

Reflections and Insights on the Evolution of the Biological Remediation of Contaminated Soils

“…Interestingly, within the agricultural arena, some authors (Baez-Rogelio et al, 2017) emphasized the possibility of inoculating microorganisms able to simultaneously carry out both plant growth promotion and the bioremediation of contaminated soils derived from intensive farming. For the selection of plant growth-promoting bacteria, which will later be inoculated as single strain formulations or consortia of different strains (in order to emulate more natural rhizomicrobiome systems) (Rosier et al, 2021), several plant growth-promoting traits are normally tested:…”