Selection and characterization of salt-tolerant plant growth promoting bacteria associated with the endosphere and rhizosphere of perennial glasswort from the Apulia Region (Italy)

Soil salinization threatens global agricultural productivity, making halotolerant plant growth promoting bacteria (PGPB) crucial for sustainable farming in marginal areas. This study isolated and characterized PGPB from perennial glasswort (<i>Arthrocaulon macrostachyum</i>) collected at two sites in Margherita di Savoia, Apulia (Italy), during spring 2023. From rhizosphere and endosphere samples, 110 bacterial isolates (100 rhizobacteria, 10 endophytes) were obtained and characterized. Functional screening revealed: 18 isolates (16%) capable of phosphate solubilization, 25 isolates (23%) for silicon solubilization, 20 isolates (18%) producing indole acetic acid, 34 isolates (31%) producing siderophores, and 50 isolates (45%) demonstrating salt tolerance above 10% NaCl, with 28 isolates (25%) tolerating concentrations up to 17.5%. Using RAPD-PCR differentiation and Principal Component Analysis of PGPB traits, three promising halotolerant candidates were selected: <i>Pseudomonas</i> sp. (105S), <i>Bacillus safensis</i> (80S), and <i>Peribacillus frigotolerans</i> (114S), each exhibiting complementary plant growth promoting characteristics. These isolates represent valuable candidates for future field validation as biofertilizers in salt-affected agricultural systems.