## 5 Conclusions  
Salinization is one of the major challenges for agriculture, as it limits crop productivity. However, the use of PGPR can greatly improve plant fitness and crop productivity, by limiting the impacts of soils. In this work, we have characterized four new halophilic/halotolerant bacterial strains with potentially beneficial properties for plants in vitro, at different concentrations of NaCl. In fact, all these isolated bacteria showed PGP features, such as production of IAA, ammonia, siderophores, and ACC deaminase. Currently, the effects of salt on PGP features remain little known, and few studies have described these effects in _Bacillus_ species, _Pseudomonas_ spp., and some enterobacteria. Even less is known for _Halomonas_. Here, we have shown how different PGP activities in _Bacillus_ and _Halomonas_ species are differentially regulated by NaCl, and in a strain-dependent manner. In the same bacterium, a specific activity can be strongly inhibited by salt, and another expressed only in its presence, whereas in another strain, the same activity can has a different or opposite reaction. Our study contributes to expanding the knowledge on the effects of salt on the PGPR activities, highlighting how halotolerance is not a sufficient characteristic for such microorganisms to be useful for plants under salt-stress conditions, emphasizing the importance of considering the use of bacterial consortia in experimental soil recovery plans and selecting them based on their responses to NaCl. In this way, it is expected that the greatest number of growth-promoting functions will be kept active at high levels in a wide range of salt concentrations. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13074320/s1](https://www.mdpi.com/article/10.3390/app13074320/s1)]([https://www.mdpi.com/article/10.3390/app13074320/s1](https://www.mdpi.com/article/10.3390/app13074320/s1)). Figure S1: Phytotoxicity experiment with _Zen mays_ L. cv. DDK 7730. Plants (5 replicates) are exposed to increasing NaCl concentration, cultivated in greenhouse with a photoperiod of 16 h of light and 8 h of dark and at constant temperature of 21 \({}^{\circ}\)C. The picture was taken one month before the material harvesting. At the end of the experiment, all seedlings treated with NaCl 100 mM were not anymore alive. The effects of increasing NaCl concentration (control, 15, 35, 55, 75, 100 mM) on maize seedlings are shown from left to right; Figure S2: Biomass dry weight of Zea mays L. at the end of experiment (Figure S1). Values are the means of 5 replicates. Letters indicate statistical significance. NA = \"not available\" because the seedlings were dead. The colors indicate different NaCl concentrations; Table S1: PCR conditions; Table S2: 16S rDNA sequence length of isolated strains. **Author Contributions:** Conceptualization, G.V., S.C. and G.O. ; methodology, G.O., G.V. and L.D.S. ; software, G.O. and L.D.S. ; validation, G.V., S.C., A.C. and F.G.; formal analysis, G.O., L.D.S. and G.V. ; investigation, G.O., L.D.S. and G.V. ; resources, S.C. and G.V. ; data curation, G.O., G.V., L.D.S., S.C. and F.G.; writing--original draft preparation, G.O., G.V. and L.D.S. ; writing--review and editing, S.C., F.G. and A.C.; visualization, G.O., G.V. and L.D.S. ; supervision, S.C., F.G. and A.C.; project administration, Department of Chemistry and Biology--University of Salerno; funding acquisition, S.C. and G.V. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported by MIUR-FARB 2021 (S.C.) and MIUR FARB 2022 (G.V.) funding from University of Salerno/Department of Chemistry and Biology.