ROMERO Fernando Matias
congresos y reuniones científicas
Shifts in the bacterial rhizospheric communities of canola plants in response to seed inoculation with a beneficial endophyte
Simposio; Young Microbiologists Symposium; 2020
Many endophytic bacteria promote plant growth and protect them against pathogens. We have isolated and characterized a Pseudomonas viridiflava endophytic strain that colonizes the apoplast of canola leaves. This isolate showed antagonism against different phytopathogens, such as Xanthomonas campestris, in vitro and in planta. The mechanisms proposed to be involved include the production of antimicrobial compounds as well as the ability to induce defence mechanisms mediated by defense hormones in the host. The aim of this work was to analyse the modifications in the abundance of rhizospheric bacterial communities in canola plants in response to P. viridiflava inoculation. Total DNA was purified from rhizospheric soil from seed and mock-inoculated plants. For bacterial communities, 16S gene libraries were constructed with the universal primers 341F - 805R and sequenced thought the Illumina MiSeq technology. Pair-end sequences were joined, aligned and clustered into Operational Taxonomic Units (OTUs) using the open reference strategy. Taxonomic identity was assigned by the Greengenes database. Singletons, chloroplasts, and mitochondria were filtered out of the analysis. The OTUs table was subsampled and transformed for the further diversity analysis. First, we measured different indexes regarding communities? diversity, such as richness, Simpson and Shannon for alpha diversity and Bray-Curtis or Jaccard for beta diversity, we found no differences on every index analysed between control and inoculated samples. Taxonomic composition of both communities was similar. The dominant phylum of both, control and inoculated communities were Proteobacteria (33-41%), Actinobacteria (16-25%) and Acidobacteria (10-13%). The evaluation of abundances at phylum level showed that Choloroflexi, Firmicutes and Actinobacteria were increased in the rhizhosphere of P. viridiflava-inoculated plants. While, the phylum Spirochaetes was diminished in the inoculated samples. When we further analysed in depth the phylum Firmicutes we observed that the order Bacillales was increased in inoculated samples, while the Clostridiales was reduced. In the case of Actinobacteria, the class Actinobacteria was the one showing changes, particularly the orders Micrococcales and Actinomycetales were increased in response to endophyte inoculation. Other phylum broadly involved in relation with plants is Proteobacteria, which include several plant pathogens, such as X. campestris. In this way, we observed that the order Xanthomonadales was decreased in response to the inoculation with P. viridiflava. On the other hand, we measured by qPCR the abundance of different genes involved in nitrogen metabolism, such as nitrogenase (nifH) and nitrous oxide reductase (nosZ), production of DAPG (phlD) and phosphate solubilisation, such as alkaline phosphatase (phoD). Thus, we observed an increase in abundance of the genes nosZ and phoD upon inoculation with the beneficial endophyte, while the other genes analysed did not change between treatments. Altogether, our results show that inoculation with the beneficial endophyte P. viridiflava did not affect diversity on bacterial communities associated with canola rhizosphere. However, it modifies the composition of specific taxons that could be involved in the growth and defence of the plants host such as Bacillales or Actinomycetales. Moreover, endophyte inoculation induces the accumulation of genes involved in nitrogen metabolism and phosphate solubilisation. In conclusion, besides the direct effect of endophyte inoculation, it could have an indirect effect on plant health and growth by recruiting different microorganisms with beneficial characteristics.