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ThesisItem Open Access A study of sulphur metabolizing bacteria from tea garden soil for improving sulphur uptake in crop plants.(2023) Baruah, Manjistha; Barooah, MadhumitaSulphur, an important element for plant growth, is required for the synthesis of several essential vitamins, amino acids, initiation of enzymes, formation of glucosides, chlorophyll, and glucosinolates. Bacteria with sulphur metabolizing ability are at the center of sulphur cycling taking part in the oxidation, reduction, assimilation and dissimilation of sulphur in the entire ecosystem. In acidic soil, the amount of sulphur is less which affects the plant growth. Sulphur metabolizing bacteria with low pH tolerance can be used as bioinoculum to facilitate sulphur availability to the crop plants. Towards this end, sulphur metabolizing bacteria was isolated from acidic soils and characterized for sulphur metabolizing activity. The most efficient sulphur metabolizing, acid tolerant bacteria along with plant growth promoting activities isolated was identified as Priestia aryabhattai MBM3 as deduced from morphological, biochemical and molecular studies. The genes involved in sulphur metabolic pathway in the bacterial isolate grown in acid stress were upregulated during the lag phase indicating to the low sulphur availability during acid stress and hence higher expression of the gens. Further studies of the isolate for plant growth promotion in Brassica campestris L. variety JT-90-1 (Jeuti) was evaluated through pot experiments. The pot soils with pH 5 were supplemented with 100%RDF (T1), 50% RDF+bio-primed seeds (T2), bio-primed seeds (T3), along with an absolute control. Agronomic and physiological traits in relation to plant height, number of leaves, flavonoid content and total carbohydrate fared better in plants treated with bacteria (T2 and T3) than in control and T1 plants. At a molecular level, the plant sulphur transporters (SULTR1 and SULTR4) and pathway genes such as APS reductase and sulfite reductase had lower expression in roots indicating to favorable uptake of sulphur by the plant and its subsequent transfer to the other parts. This was evidenced by higher expression of the transporter genes in leaves signifying its uptake followed by its subsequent assimilation by the pathway genes viz. ATP sulphurylase, APS reductase, and sulfite reductase. However, in the control and T1 plants, a significant high expression of APS reductase was observed indicating over production of sulfite. Increased sulfite production is reported to affect chlorophyll content and stunted growth in plants as evidenced by agronomic and physiological traits of the control and T1 plants. The above results suggest that isolate MBM3 was able to elicit a sulphur uptake response in Brassica campestris grown in acidic soil of pH 5 as compared to control revealing a delicate symbiosis between plant and bacterial signaling pathways. Further studies to unravel the plant signaling pathways involved in evoking an enhanced sulphur metabolism due to bacterial treatment will shed more light into role of the bioinoculum before it is taken to the field.
