ABSTRACT
Sulfur-oxidizing bacteria (SOB) are versatile microorganisms known for their ability to oxidize various reduced sulfur compounds, namely, elemental sulfur (S0), hydrogen sulfide (H2S), tetrathionate (S4O62-), and trithionate (S3O62-) to sulfate (SO42-). In this study, out of twelve SOB isolates from rice rhizosphere, five were screened based on their sulfur oxidation potential, viz., SOB1, SOB2, SOB3, SOB4, and SOB5, and were identified as Ochrobactrum soli SOB1, Achromobacter xylosoxidans SOB2, Stenotrophomonas maltophilia SOB3, Brucella tritici SOB4, and Stenotrophomonas pavanii SOB5, respectively. All the isolates displayed chemolithotrophic nutritional mode by consuming thiosulfate and accumulating trithionate and tetrathionate in the growth medium which is ultimately oxidized to sulfate. The strains were authenticated with the production of thiosulfate oxidizing enzymes such as rhodanese and sulfite oxidase. Despite their tendency to oxidize reduced sulfur compounds, B. tritici SOB4 and S. pavanii SOB5 were also found to possess phosphate and zinc solubilization potential, acetic acid, and indole acetic acid (IAA) production and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The presence of sulfanyl (R-SH) groups was noticed in the A. xylosoxidans SOB2. Elemental sulfur conversion into sulfate was noted in the S. maltophilia SOB3, and hydrogen sulfide conversion into sulfate was observed in the Ochromobacter soli SOB1. Sulfur oxidation potential coupled with beneficial properties of the isolates widen the knowledge on SOB.
Subject(s)
Hydrogen Sulfide , Oryza , Sulfur Acids , Thiosulfates , Rhizosphere , Oxidation-Reduction , Bacteria/genetics , Sulfur , Sulfur Compounds , SulfatesABSTRACT
PURPOSE: Rice is the prominent crop of world and it frames the important component of food chain. But, long duration of highly preferred rice varieties requires more water and are prone to biotic and abiotic stresses. Short duration rice varieties serve as a promising alternative in such cases. Hence, the present study was taken up to induce early flowering mutants in popular rice variety Bapatla 2231 (BPT 2231), a long duration medium slender rice variety using gamma rays and Ethyl Methane Sulfonate (EMS) treatment combinations. MATERIALS AND METHODS: Five hundred well filled and viable grains of optimum moisture content (12%) were subjected to irradiation with 8 doses comprising 100 Gy, 200 Gy, 300 Gy, 350 Gy, 400 Gy, 450 Gy, 500 Gy and 600 Gy treatments. For combination treatments, the irradiated seeds of gamma rays were further treated with 30 mM concentrations of Ethyl Methane sulfonate (EMS). The irradiated population were raised up to M3 generation for the identification of early maturing mutants. The isolated early maturing mutants in M3 generation were characterized for phenotypic, biochemical and grain qualities. RESULTS: The frequency of desirable early maturing mutants was observed more in combination treatments than the individual treatments of gamma rays. A total of 34 early maturing mutants (M) with variation for grain quality and biochemical traits were obtained. The mutants M-1, M-3, M-5, M-32, and M-34 were high yielding with fine grain type. The mutants M-4, M-17, M-18, M-19, M-20, and M-26 were high yielding with bold grain type. The mutants M-22, M-23, M-24, M-27, and M-28 were high in nutrient content. The early mutants matured 40-50 days earlier than control. CONCLUSION: In this variety, the combination treatments showed higher mutation frequency, mutagenic effectiveness and efficiency than the gamma rays in induction of both chlorophyll and viable mutants. This study revealed that the combination treatments were more effective in inducing early mutants than the gamma ray treatments alone. The early maturing mutants can be released as variety after evaluation under different yield trials and the mutants with increased nutrient content and varied grain quality can be utilized in hybridization/heterosis breeding programs for rice crop improvement.
