Isolation and characterization of salt-tolerant Staphylococcus spp. as plant-growth-promoting rhizobacteria enhancing rice seedling growth under salinity stress

Abstract

Salinity is a major abiotic stress that limits crop productivity worldwide, especially in coastal areas where climate change and seawater intrusion are worsening soil salinization. Plant growth-promoting rhizobacteria (PGPR) offer an eco-friendly solution to reduce salinity effects by improving nutrient uptake, osmotic balance, and antioxidant defenses in plants. This study aimed to isolate and characterize salt-tolerant PGPR from soils in Sylhet, Bangladesh, and assess their ability to improve rice (Oryza sativa cv. BRRI Dhan-29) growth under salt stress. Fifty-five bacterial isolates were collected; 11 of these tolerated salinity levels up to 20 % NaCl and displayed multiple PGP traits. Four strains, such as AT-2, AW-2, M-15, and F-6, showed superior performance in forming biofilm (up to 2 M NaCl) and producing indole-3-acetic acid (up to 8.94 mg/mL), ammonia (up to 5.88 mg/mL), and exopolysaccharides (0.40 mg at 2 M NaCl). Inoculating rice seedlings with these strains improved growth under both normal and saline (200 mM NaCl) conditions, increasing root length by up to 68 %, shoot length by 37 %, and total chlorophyll content by approximately 50 %, while decreasing hydrogen peroxide accumulation by up to 34 %. Molecular identification by 16S rRNA sequencing confirmed these isolates as Staphylococcus species, revealing their new role as PGPR capable of enhancing salt-stress tolerance in rice. These results highlight the potential of native, salt-tolerant bacterial strains as sustainable bioinoculants to boost crop resilience in saline-affected areas. Although this strain is known as a human and animal pathogen, we identified it as a PGPR that can improve salt-stress resilience in rice plants.