## 1 Introduction  
Soil salinity is an environmental problem that challenges agriculture worldwide by imposing the threat of reduced crop productivity [1]. Some plants, designated as halophytes, are adapted to grow and complete their life cycle in saline soils or sediments, These plants are able to grow and reproduce under salinities >200 mM NaCl [2], whereas most non-halophytes can withstand moderate salinities but begin to express stress signals at salinities higher than 80 mM of NaCl [3]. The association with microorganisms has been proven as directly and/or indirectly involved in the improvement of plant growth,nutrition and development, and in the overall adaption of halophytes to saline stress [4; 5; 6; 7; 8]. Bacterial communities living in the vicinity of plant roots (rhizosphere) and establishing positive interactions with host plants are known as plant-growth promoting rhizobacteria (PGPR). Activities of PGPR in general contribute to a more efficient acquisition of nutrients by the plant through nitrogen fixation activity, increased availability of minerals (phosphate solubilization) or production of siderophores (iron acquisition). In halophytes, rhizobacteria increase the tolerance of plants growing in saline soils by regulating the concentration of ethylene, via the enzyme ACC deaminase and the production of bacterial metabolites that act as phyto-hormones (e.g., IAA (3-indole acetic acid), ABA (abscisic acid), GA3 (gibberell acid)) [9]. In comparison with rhizobacteria, bacteria colonizing root plant tissues, known as endophytes, establish direct interactions with plant cells and have shown to stimulate plant growth and/or natural resistance to stress in the same way as rhizobacteria [10; 11]. _Salicornia ramossissima_ J. [PERSON] is an annual halophyte of the Chenopodiaceae family, widely distributed in salt marshes of the Iberian Peninsula, Northwest Africa [12; 13] and the Mediterranean European coast [14; 15]. _S. ramossissima_ and the _S. europaea_ aggregate in which _S. ramossissima_ is included [16] have been gaining economic value as gourmet food products, fodder for animals, oil seeds and raw material for the extraction of dietary fiber and high added-value metabolites [17; 18; 19; 20]. However, information on the microbiome of _S. ramossissima_ and is still relatively scarce in comparison to other halophytes. Culture-independent analyses indicate that there are significant differences in the structure of bacterial communities associated with different organs and that, in general, diversity is higher in the rhizosphere than among root endophytes [21] and higher in roots than in shoot tissues [22]. Another interesting trait is that the fine structure of these communities is distinctively imprinted by sediment properties [22], particularly salinity [23]. Culture-dependent approaches directed to _Salicornia_ species provide PGPR that effectively attenuates saline stress effects in halophytes [24; 25; 26; 27] and non-halophyte crops [28; 29]. Halotolerant Proteobacteria (_Pseudomonas_, _Variovorax_, _Xanthomonas_), Firmicutes (_Bacillus_, _Planococcus_, _Staphylococcus_) and Actinobacteria (_Arthobacter_, _Curbobacterium_, _Microbacterium_) exhibiting plant-growth promoting traits have been retrieved from the endosphere or rhizosphere of _S. ramossissima_ (or _S. europaea_) [24; 25; 28; 29; 30]. However, there is evidence that salinity may impose a strong intraspecific variability on the composition and structure of root-associated plant-growth promoting bacterial guilds, like diazotrophs [30]. Information on the relation between salinity and other sediment properties and the diversity of plant-growth promoting isolates associated with _S. ramossissima_ is scarce. This knowledge would not only expand our understanding of the contribution of particular root-associated bacterial taxa to the adaptation of the _S. ramossissima_ to stress but would also support the tailored design of PGPR consortia to be applied in defined plant hosts and in particular environmental contexts.