Microbiome profiling reveals that Pseudomonas antagonises parasitic nodule colonisation of cheater rhizobia in Lotus

Crosbie, Duncan (2022): Microbiome profiling reveals that Pseudomonas antagonises parasitic nodule colonisation of cheater rhizobia in Lotus. Dissertation, LMU München: Fakultät für Biologie

Abstract

Nitrogen fixation is carried out inside nodules of legumes by symbiotic rhizobia. Rhizobia dominate the nodule microbiome, however, other non-rhizobial bacteria also colonise root nodules. It is not clear whether these less abundant nodule colonisers impact nodule function. In order to investigate the relationship between the nodule microbiome and nodule function as influenced by the soil microbiome, we used a metabarcoding approach to characterise the communities inside Lotus burttii, Lotus japonicus and Lotus corniculatus nodules from plants that were either starved or healthy, resulting from inoculations with different soil suspensions in a closed pot experiment. We found that the nodule microbiome of all tested Lotus species differed according to inoculum, but only that of L. burttii varied with plant health. Using a machine learning algorithm, we found that out of all the non-rhizobial bacteria inside the L. burttii nodules, amplicon sequence variants (ASVs) corresponding to Pseudomonas were the most indicative signatures of healthy plants. Rhizobium ASVs were the most indicative of a starved L. burttii plant nodule. Network analysis revealed that there were exclusively negative significant correlations between Rhizobium and Pseudomonas ASVs and both positive and negative correlations between Pseudomonas and Mesorhizobium ASVs. This was supported by a co-inoculation experiment on L. burttii that revealed fluorescently tagged Pseudomonas could co-colonise nodules formed by Mesorhizobium, but not those formed by Rhizobium. Further evidence for the potential plant benefit of Pseudomonas presence was seen in a co-inoculation with Rhizobium on L. japonicus. The number of ineffective nodules induced by the Rhizobium isolate was reduced when inoculated together with a Pseudomonas nodule isolate. The same reduction in ineffective nodules was not seen in L. burttii. These results support the hypothesis that legume nodule endophytes influence the overall outcome of the root-nodule symbiosis, albeit in a plant host-specific manner. In addition, a novel Mesorhizobium species, Mesorhizobium norwegicum, was physiologically and chemotaxonomically characterised.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 18. November 2022
• 1. Bericht­erstatter:in: Marín, Macarena