Joana Jesus1, Júlio Maciel1, Rogério Tenreiro1,4, Cristina Máguas1,2 and Helena Trindade1,3
1Universidade de Lisboa, Faculdade de Ciências, 1749-016 Lisboa, Portugal
2cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
3CESAM – Centro de Estudos do Ambiente e do Mar, Faculdade de Ciências, Universidade de Lisboa, CBV, 1749-016 Lisboa, Portugal
4BioISI – Biosystems and Integrative Sciences Institute, Portugal
Invasive species can cause considerable damage in ecosystems. In Portugal and in other coastal areas in the Atlantic coast, Acacia longifolia is one of these species. Native from Australia and Tasmania, it was introduced for ornamental purposes and nitrogen fixation to enrich soils. However, it competes with native species for natural resources, outgrowing them and changing the soil characteristics. One of the factors that drive A.longifolia dispersion is fire, by promoting seed germination. In the initial plant growth stages, nodules are structures formed de novo in the roots and arise due to symbiosis established with nitrogen-fixing bacteria (NFB), mainly from the Rhizobiaceae family. These bacteria are responsible for nitrogen fixation inside the nodules, as they develop in bacteroids inside the plant cells. These NFB can also be called plant growth promoting bacteria (PGPB), given the direct impact they cause in plants. Although a characteristic trait of acacias is promiscuity in symbiotic partners, the extent of how this is related to invasiveness is not clear. Considering this, native legumes can be a source of rhizobia for the invaders, but it can also be possible that some symbionts are already “buried” in seeds.
This study aimed to (i) understand how fire influences nodule development and functioning, (ii) identify the major microorganisms involved in early symbiosis and what is their succession following a fire, and (iii) compare bacteria found in nodules and in the seeds. To perform this, root nodules from 20-60 cm long young plants of A. longifolia were collected in the field (before and after a fire). The surface was sterilized and plated in nitrogen-free medium to isolate endogenous bacteria. Additionally, seeds were also plated after surface sterilization. A collection of ca. 180 bacterial isolates was obtained from the nodules and seeds. Genomic fingerprinting of isolates was performed by PCR amplification with csM13 and (GTG)5 universal primers and assessment of diversity was based on dendrograms with Pearson similarity coefficient and UPGMA. 16S rRNA gene sequencing of representatives from the main genomic clusters is also underway to identify the relevant bacterial genus/species involved in this symbiosis and enlighten the role of seeds as a reservoir for A. longifolia symbiotic partners.