Acinetobacter lwoffii 5M1 mediated biological oxidation enhances elemental sulphur efficiency for sodic soil amelioration and its crop productivity

BACKGROUND: Native sulphur-oxidising microbial communities play a crucial role in the effectiveness of elemental sulphur (S°)-based reclamation of sodic soils. This study reports, for the first time, the sulphur oxidation (S°-oxidation) capability of Acinetobacter lwoffii strain 5M1, isolated from highly saline soil (electrical conductivity of 36 dS m⁻¹) surrounding a hot-water spring. RESULT: The strain released appreciable amounts of plant growth-promoting compounds, including ammonia and indole-3-acetic acid (IAA). A. lwoffii 5M1 formed biofilms around S°-particles in growth media. It harbours the soxA (720 bp), soxB (590 bp), and soxY (329 bp) genes, which form the core component of the Sox gene cluster. Inoculation of S° with A. lwoffii 5M1 caused a 15.3-39.1% increase in S°-oxidation in soil of varied sodicity with pHs ranging from 9.1 to 10.5. The improved oxidation was associated with a decline in bicarbonate and alkalinity and a simultaneous increase in Ca²⁺, Mg²⁺, and inorganic P content in the soil solution. Integrating strain 5M1 with S°enhanced rice and wheat yields by 6.45-28.8% than S° alone. CONCLUSION: This study concludes that A. lwoffii strain 5M1, with its dual function of S° oxidation and plant growth promotion, represents a promising bio-inoculant for rapid and efficient sodicity reclamation.