Quorum sensing communication: Bradyrhizobium‐Azospirillum interaction via N‐acyl‐homoserine lactones in the promotion of soybean symbiosis

Abstract

Quorum‐sensing (QS) mechanisms are important in intra‐ and inter‐specific communication among bacteria. We investigated QS mechanisms in Bradyrhizobium japonicum strain CPAC 15 and Azospirillum brasilense strains Ab‐V5 and Ab‐V6, used in commercial co‐inoculants for the soybean crop in Brazil. A transconjugant of CPAC 15‐QS with partial inactivation of N‐acyl‐homoserine lactones (AHLs) was obtained and several parameters were evaluated; in vitro, CPAC 15 and the transconjugant differed in growth, but not in biofilm formation, and no differences were observed in the symbiotic performance in vivo. The genome of CPAC 15 carries functional luxI and luxR genes and low amounts of three AHL molecules were detected: 3‐OH‐C12‐AHL, 3‐OH‐C14‐AHL, and 3‐oxo‐C14‐AHL. Multiple copies of luxR‐like genes, but not of luxI are present in the genomes of Ab‐V5 and Ab‐V6, and differences in gene expression were observed when the strains were co‐cultured with B. japonicum; we may infer that the luxR‐genes of A. brasilense may perceive the AHL molecules of B. japonicum. Soybean symbiotic performance was improved especially by co‐inoculation with Ab‐V6, which, contrarily to Ab‐V5, did not respond to the AHLs of CPAC 15. We concluded that A. brasilense Ab‐V5, but not Ab‐V6, responded to the QS signals of CPAC 15, and that the synergistic interaction may be credited, at least partially, to the QS interaction. In addition, we confirmed inter‐ and intra‐species QS communication between B. japonicum and A. brasilense and, for Azospirillum, at the strain level, impacting several steps of the symbiosis, from cell growth to plant nodulation and growth.

Enhancing Symbiotic Nitrogen Fixation and Soybean Growth through Co-Inoculation with Bradyrhizobium and Pseudomonas Isolates

“…Besides, Pseudomonas fluorescens has been found to enhance the nitrogen fixation of soybean through promoting the growth and colonization of Bradyrhizobium japonicum [45]. Soybean symbiotic performance was improved by co-inoculation with Bradyrhizobium japonicum and Azospirillum brasilense through quorum-sensing communi-cation [46]. In this study, all the Pseudomonas isolates showed potential to produce IAA, which might influence the symbiotic outcome by altering phytohormonal homeostasis of soybean [47].…”

Biopelículas en la rizósfera y su papel en la producción de compuestos antimicrobiales en el suelo

“…Uno de los mecanismos por los que se produce esta comunicación es a través del denominado Quorum Sensing (QS). El QS en bacterias puede describirse como: un mecanismo de comunicación intra o interespecífico, en el que intervienen mediadores químicos (llamados autoinductores) capaces de inducir respuestas dependientes de la densidad de la población (Dos Santos Lima et al, 2019). El QS en bacterias constan de dos componentes principales: una proteína receptora y un autoinductor.…”

“…La unión del autoinductor a su receptor activa el gen diana, que luego realiza la función correspondiente en bacterias (Yi, Dong, Grenier, Wang y Wang, 2021). Muchas bacterias Gram negativas utilizan autoinductores como las N-acil-homoserina lactonas (AHL) para controlar la expresión génica (Dos Santos Lima et al, 2019). El QS en estas bacterias suele ser un sistema de dos componentes integrado por una sintasa (LuxI), responsable de la producción de las moléculas autoinductoras, y un receptor sensor (LuxR), responsable de la detección de las moléculas en el ambiente (Barriuso y Martínez, 2018).…”

Screening the maize rhizobiome for consortia that improve Azospirillum brasilense root colonization and plant growth outcomes

“…With this array of benefits, significant effort has been given to understanding the microbial interactions that influence the association and colonization of A. brasilense and other diazotrophic bacteria with non-leguminous maize (Zea mays) crops (Dent and Cocking, 2017;Oliveira et al, 2018;Van Deynze et al, 2018). Prior studies have also shown that co-inoculation of A. brasilense with complementary organisms such as Bradyrhizobium (Wang et al, 2018;dos Santos Lima Fagotti et al, 2019) and cyanobacteria isolates (Hungria et al, 2010;Verma et al, 2011;Ferreira et al, 2013;Bashan et al, 2014) improves maize yield. This suggests that A. brasilense applied in a symbiotic, multi-species consortium may be key for its improvement as a biofertilizer.…”