## 1 Introduction  
The worldwide enhancement of both human population and the associated environmental deterioration has the unfortunate influence that global food manufacture might soon become unsatisfactory to nourish all of the world's people. It is therefore crucial to increase farming productivity within the next few decades [1]. On the other hand, in the natural environment, plants are constantly exposed to various abiotic and biotic factors, which may affect their increase and yield [2]. Stress is described as any external abiotic (salinity, water, heat) or biotic (herbivore) constraint that restricts the level of photosynthesis and decreases a plant's capacity to transform energy to biomass [3]. Especially, abiotic factors are main constraints for global food security, food quality, and crop productivity [4].  
Salinity is recognized to affect almost one fourth of world cultivable land, a main cause of desertification [5]. It is responsible for the degradation of 10 million ha of world farming per year [6], influencing about 1 million ha in the European Union, mainly in the Mediterranean countries. Various salt ions in the soil, that are dissoluble in water like chloride (Cl\({}^{-}\)), sodium (Na\({}^{+}\)), magnesium (Mg\({}^{2+}\)), potassium (K\({}^{+}\)), bicarbonate (HCOO\({}^{3-}\)), sulfate (SO4\({}^{2-}\)), carbonate (CO\({}_{3}\)\({}^{2-}\)), and calcium (Ca\({}^{2+}\)) may cause salinization [7]. Salinization is a natural process in semiarid and arid zones and may additionally be stimulated by anthropogenic practices. It significantly influences land fertility [8], and therefore comprises a huge effect on food security and economy at local, regional, and global levels [7]. Although plant tolerance to salinity varies with species and even varieties as well as with biotic and abiotic factors, the growth of most of the plant cultures is negatively influenced by salinity [9; 10]. Excess accumulation of salts in the root zone often deteriorates the soil properties, viz. physical, chemical, and biological to such an extent that crop production is adversely affected [11]. In addition, excessive salinity in soil suppresses growth, decreases species diversity, and alters the community composition of plants; however, the effect of salinity on soil microbial communities is poorly understood [12].  
Some of the microorganisms that live in close combination with the plant roots ensure a significant function in improving plant growth [13], and/or in stress mitigation of crops cultivated under salinity conditions [14]. Plant growth-promoting bacteria (PGPB) may be active through a diversity of processes [15] including the regulation of the transcription of various genes and cellular communication through quorum sensing [16], and mainly by production of various secondary metabolites [17]. For instance, through the production of exopolysaccharides (EPS), indole acetic acid (IAA), nitrogen fixation, and P-solubilization [18]. PGPB may form symbiotic relations with plants and improve their performance in the face of salinity stress [19; 20]. Moreover, PGPB are an environmentally sustainable tool to mitigate the impacts of salinity on crop yields [2].