Halophyte-Derived Kushneria Strains Enhance Salt Tolerance and Rhizosphere Dynamics in Cabbage

Halophytic plants harbour salt-tolerant bacteria that enhance resilience to salinity. In this study, two highly halotolerant Kushneria isolates, K. konosiri (Kk) and K. marisflavi (Km), were obtained from the halophyte Suaeda maritima. Both strains tolerated up to 25% NaCl and promoted Arabidopsis thaliana growth under salt stress by producing indole-3-acetic acid, proline, and extracellular polysaccharides that mitigated osmotic stress. Inoculation with Kk or Km increased shoot and root biomass and reduced intracellular Na⁺ and reactive oxygen species. Their agricultural potential was tested in cabbage (Brassica rapa), where both isolates alleviated salinity-induced growth inhibition. A combined inoculum (Kkm) showed enhanced efficacy, significantly increasing shoot biomass (1.26-fold vs. Kk; 1.23-fold vs. Km) and dry weight (1.19-fold vs. Kk; 1.13-fold vs. Km). Kkm treatment also improved the K⁺/Na⁺ ratio and proline accumulation. Microbial profiling revealed that Kkm enriched Bacillus species in the rhizosphere and promoted greater biofilm formation than single strains. These findings demonstrate that Kushneria isolates function as salt-tolerant plant growth-promoting bacteria, enhancing ion homoeostasis, stress protection, and rhizosphere restructuring. This study highlights the potential of halophyte-derived microbial consortia to improve crop salt tolerance in agriculture.