Soil Bacterium Boosts Sulphur Oxidation and Crop Yields in Sodic Soils

The bacterium Acinetobacter radioresistens Ke–5 significantly enhanced the oxidation of elemental sulphur in sodic soils and, when applied together with sulphur, raised rice and wheat yields by 4.8 to 19.3 per cent compared with sulphur alone, according to a peer-reviewed research article published open access in the journal Microbial Ecology on 24 October 2026. The study, led by Parul Sundha, Arvind Kumar Rai and colleagues including Rajender Kumar Yadav, evaluated the strain under laboratory incubation and lysimeter conditions using sodic soils collected from different agro-ecologies, with pH values of 9.8 to 10.9 and exchangeable sodium percentage ranging from 62.5 to 98.2 per cent.

The starting point of the work, as stated in the abstract, is that native sulphur-oxidizing communities are essential for the success of elemental sulphur-based sodicity reclamation. Elemental sulphur must be oxidized before it can act on soil alkalinity, and the researchers set out to characterize the sulphur-oxidizing capacity of a single strain, Ke–5, across soils of varied sodicity. Inoculation of sodic soils with pH 9.1 to 10.5 enhanced elemental sulphur oxidation by 3.7 to 29.4 per cent, the measured range reported across the tested conditions.

Laboratory characterization showed that Ke–5 carries several beneficial traits. The strain produces titratable acidity, secretes ammonia and the plant hormone indole-3-acetic acid, and solubilizes phosphorus and zinc. Polymerase chain reaction analysis confirmed the presence of the soxA, soxB and soxY genes, which are associated with the Sox gene cluster for sulphur oxidation. The strain also formed biofilms around sulphur particles, positioning itself at the substrate it oxidizes.

The chemical consequences of inoculation were consistent with enhanced sulphur oxidation. Enhanced oxidation was associated with reduced bicarbonate concentration and lower total soil alkalinity, along with increased calcium and magnesium concentrations in the soil solution. The increased calcium and magnesium reduced the sodium adsorption ratio by 32 to 41 per cent and, according to the authors, potentially facilitated the displacement of sodium from soil exchange sites.

Agronomic performance was assessed in a rice-wheat cropping system under lysimeter conditions, with treatments allocated following a randomized block design with five replications. The combined application of strain Ke–5 with elemental sulphur caused a 4.8 to 19.3 per cent increase in rice and wheat yield compared with the application of elemental sulphur alone. These yield figures come from the lysimeter experiments and have not been reported for open field conditions in this study.

The authors conclude that A. radioresistens Ke–5, with its sulphur-oxidation and plant growth-promotion capabilities, can be a promising option for improving the efficiency of sulphur-based reclamation and plant growth promotion in sodicity-affected soils. They are explicit, however, that the evidence comes from laboratory incubation and lysimeter experiments rather than field trials.

The study also states clearly what remains before practical adoption: field validation and more comprehensive genomic and phenotypic safety assessments are required before the strain can be adopted as a bioinoculant. This limitation is part of the published findings, not an external caveat, and it defines the boundary between the reported lysimeter results and any claim about performance under farming conditions.

Within that scope, the study reports a coherent set of linked measurements for one strain: gene-level confirmation of sulphur-oxidation machinery, measurable increases in sulphur oxidation across a range of sodic soils, associated shifts in soil solution chemistry including a 32 to 41 per cent reduction in the sodium adsorption ratio, and yield gains of 4.8 to 19.3 per cent in a rice-wheat rotation under lysimeter conditions. Whether these effects hold at field scale, and whether the strain is safe for environmental release, are the questions the authors identify as outstanding.

Subject of Research: Sulphur-oxidizing bacterium Acinetobacter radioresistens Ke–5 for sodic soil reclamation

Article Title: Acinetobacter Radioresistens Ke–5 Oxidises Elemental Sulphur in Sodic Soil and Affects Crop Performance

Article References: Sundha, P., Rai, A. K., Basak, N., Chandra, P., Meena, R. L., Sharma, P. C., & Yadav, R. K. (2026). Acinetobacter Radioresistens Ke–5 Oxidises Elemental Sulphur in Sodic Soil and Affects Crop Performance. Microbial Ecology. https://doi.org/10.1007/s00248-026-02920-1

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02920-1

Keywords: Acinetobacter radioresistens, sodic soil, elemental sulphur, sulphur oxidation, soil reclamation, bioinoculant, rice-wheat cropping, sodium adsorption ratio, Sox genes, plant growth promotion, lysimeter, Microbial Ecology