Bacterial microbiome of root-associated endophytes of Salicornia europaea in correspondence to different levels of salinity

The diversity of endophytic bacteria associated with the roots of Salicornia europaea L. growing at natural (C) and anthropogenic (I) saline test sites was examined using the Miseq Illumina sequencing technique. The variability in the V3-V4 16S rRNA gene region (based on < 97% reads) was analyzed in correspondence to the -physico-chemical parameters of rhizosphere soil - and the element concentrations in the root. A higher number of OTUs were obtained among endophytes isolated from site C (highly saline soil) with 3366 OTUs and for site I -2608 OTUs and the number of common OTUs for both test sites was 1479. The dominant endophytic phyla – in both investigated test sites were: Proteobacteria, Bacteriodetes, Firmicutes, Planctomycetes, Actinobacteria, Chloroflexi, Acidobacteria, Verrucomicrobia, OD1, Chlamydiae, TM7, Fibrobacteres. The soil parameters: electrical conductivity level (ECe), organic carbon (OC), total nitrogen (Nt), calcium carbonate, sulphate, calcium, chloride, sodium, magnesium, potassium, and saturation percentage proved to play a role in shaping the diversity of bacterial endophytes in roots of S. europaea in both the test sites.The non-metric multidimensional scaling analysis revealed a positive correlation between OTUs identified for root endophytes of S. europaea at site I and in the levels of OC, Nt and Ca2+ in rhizosphere soil. Meanwhile, endophytes associated with S. europaea isolated from the site with higher salinity (C) were positively correlated with CaCO3, SP, ECe, Na+, K+, Mg2+, Cl- and SO42-. In conclusion, the level of salinity present in the rhizosphere is a crucial factor in structuring of endophytic community of S. europaea in the natural environment. This also confirms an occurrence of strong selection factors, that promotes an association which is more differentiated and salt tolerant bacterial endophytes within the host plant.