Diversity, Phylogeny and Plant Growth Promotion Traits of Nodule Associated Bacteria Isolated from Lotus parviflorus

Abstract

<i>Lotus</i> spp. are widely used as a forage to improve pastures, and inoculation with elite rhizobial strains is a common practice in many countries. However, only a few <i>Lotus</i> species have been studied in the context of plant-rhizobia interactions. In this study, forty highly diverse bacterial strains were isolated from root nodules of wild <i>Lotus parviflorus</i> plants growing in two field locations in Portugal. However, only 10% of these isolates could nodulate one or more legume hosts tested, whereas 90% were thought to be opportunistic nodule associated bacteria. Phylogenetic studies place the nodulating isolates within the <i>Bradyrhizobium</i> genus, which is closely related to <i>B. canariense</i> and other <i>Bradyrhizobium</i> sp. strains isolated from genistoid legumes and <i>Ornithopus</i> spp. Symbiotic <i>nodC</i> and <i>nifH</i> gene phylogenies were fully consistent with the taxonomic assignment and host range. The non-nodulating bacteria isolated were alpha- (<i>Rhizobium/Agrobacterium</i>), beta- (<i>Massilia</i>) and gamma-proteobacteria (<i>Pseudomonas</i>, <i>Lysobacter, Luteibacter</i>, <i>Stenotrophomonas</i> and <i>Rahnella</i>), as well as some bacteroidetes from genera <i>Sphingobacterium</i> and <i>Mucilaginibacte</i>r. Some of these nodule-associated bacteria expressed plant growth promotion (PGP) traits, such as production of lytic enzymes, antagonistic activity against phytopathogens, phosphate solubilization, or siderophore production. This argues for a potential beneficial role of these <i>L. parviflorus</i> nodule-associated bacteria.