Embrapa Soja, Londrina, Paraná, Brazil.
Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brasília, Distrito Federal, Brazil.
J Basic Microbiol. 2019 Jan;59(1):38-53. doi: 10.1002/jobm.201800324. Epub 2018 Oct 15.
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.
群体感应（QS）机制在细菌种内和种间的交流中起着重要作用。我们研究了在巴西商业化大豆共生接种中使用的慢生根瘤菌（Bradyrhizobium japonicum）菌株 CPAC 15 和固氮螺菌（Azospirillum brasilense）菌株 Ab-V5 和 Ab-V6 的 QS 机制。获得了 CPAC 15-QS 的转导子，部分失活了酰基高丝氨酸内酯（AHLs），并评估了多个参数；在体外，CPAC 15 和转导子在生长方面有所不同，但在生物膜形成方面没有差异，体内共生表现也没有观察到差异。CPAC 15 的基因组携带功能性 luxI 和 luxR 基因，并检测到三种 AHL 分子的低含量：3-OH-C12-AHL、3-OH-C14-AHL 和 3-氧代-C14-AHL。Ab-V5 和 Ab-V6 的基因组中存在多个 luxR 样基因，但没有 luxI，当这些菌株与大豆根瘤菌共培养时，观察到基因表达的差异；我们可以推断，固氮螺菌的 luxR 基因可能感知大豆根瘤菌的 AHL 分子。大豆共生表现特别是通过与 Ab-V6 的共接种得到改善，而与 Ab-V5 相反，Ab-V6 对 CPAC 15 的 AHL 没有反应。我们得出结论，固氮螺菌 Ab-V5 而不是 Ab-V6 对 CPAC 15 的 QS 信号做出反应，并且协同相互作用至少部分归因于 QS 相互作用。此外，我们证实了大豆根瘤菌和固氮螺菌之间的种间和种内 QS 通讯，对于固氮螺菌，在菌株水平上，影响共生的几个步骤，从细胞生长到植物结瘤和生长。
