Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM), UMR IRD/SupAgro/INRAE/Université de Montpellier/CIRAD - Campus de Baillarguet, Montpellier, France.
Sci Rep. 2021 Oct 22;11(1):20910. doi: 10.1038/s41598-021-00480-7.
The Bradyrhizobium sp. strain ORS285 is able to establish a nitrogen-fixing symbiosis with both Nod factor (NF) dependent and NF-independent Aeschynomene species. Here, we have studied the growth characteristics and symbiotic interaction of a glutamate synthase (GOGAT; gltD::Tn5) mutant of Bradyrhizobium ORS285. We show that the ORS285 gltD::Tn5 mutant is unable to use ammonium, nitrate and many amino acids as nitrogen source for growth and is unable to fix nitrogen under free-living conditions. Moreover, on several nitrogen sources, the growth rate of the gltB::Tn5 mutant was faster and/or the production of the carotenoid spirilloxanthin was much higher as compared to the wild-type strain. The absence of GOGAT activity has a drastic impact on the symbiotic interaction with NF-independent Aeschynomene species. With these species, inoculation with the ORS285 gltD::Tn5 mutant does not result in the formation of nodules. In contrast, the ORS285 gltD::Tn5 mutant is capable to induce nodules on NF-dependent Aeschynomene species, but these nodules were ineffective for nitrogen fixation. Interestingly, in NF-dependent and NF-independent Aeschynomene species inoculation with the ORS285 gltD::Tn5 mutant results in browning of the plant tissue at the site of the infection suggesting that the mutant bacteria induce plant defence responses.
慢生根瘤菌(Bradyrhizobium sp.)菌株 ORS285 能够与依赖 Nod 因子(NF)和不依赖 NF 的含羞草属物种建立共生固氮关系。在这里,我们研究了谷氨酸合酶(GOGAT;gltD::Tn5)突变体的生长特性和共生相互作用。我们表明,ORS285 gltD::Tn5 突变体不能将铵、硝酸盐和许多氨基酸用作生长的氮源,并且在自由生活条件下不能固氮。此外,在几种氮源上,gltB::Tn5 突变体的生长速率更快,并且/或者产生的类胡萝卜素螺旋藻黄素的产量比野生型菌株高得多。GOGAT 活性的缺失对与不依赖 NF 的含羞草属物种的共生相互作用有重大影响。与这些物种一起接种 ORS285 gltD::Tn5 突变体不会导致形成根瘤。相反,ORS285 gltD::Tn5 突变体能够在依赖 NF 的含羞草属物种上诱导形成根瘤,但这些根瘤不能固氮。有趣的是,在依赖 NF 和不依赖 NF 的含羞草属物种中,接种 ORS285 gltD::Tn5 突变体导致感染部位的植物组织变褐,这表明突变体细菌诱导了植物防御反应。