Delineation of Sulphur Bacteria Isolated from Rice Rhizosphere Soil

Crop yields are greatly reduced by sulfur-deficient conditions, as sulfur is an essential nutrient for plant growth. So, sulfur fertilizers are generally added to soils to alleviate this deficiency, usually in a reduced form, such as elemental sulfur. Despite this, microorganisms are required to oxidize reduced sulfur fertilizers into sulfate before they can be absorbed by plants. Recently, sulfur deficiency was reported widely in rice. Till date there are no suitable bio-inoculants for rice. Hence, the present study was aimed to develop a sulfur bio-inoculant for rice.

In this present investigation, totally 9 chemolithoautotropic sulfur oxidizing bacteria (3 from aerobic, 4 from wet land and 2 from SRI systems) were isolated from various rice ecosystems. Chemolithoautotrophic strain S1-3 isolated from SRI system and strain W3-1 isolated from wet land were found to efficient based on pH reduction and titrable acidity. Totally five facultative chemo lithoautotrophic sulfur oxidizing bacteria (two from wet land and 3 aerobic samples) were recovered from different rice ecosystems.

Facultative chemolithoautotrophic strain S1Y1-bLL and S2Y2-b significantly reduced the medium pH (4.3) and consumed the maximum alkali 1.7 and 1.8 mL and found to be efficient. All the isolated facultative chemolithoautotrophic sulfur were autotrophic and chemoheterotrophic in nature. Molecular characterization study revealed that strains S1Y2-aS, S1Y1- Bll, S2Y2-b, S2SA-Sa and S2Y2-an exhibited 99.5, 99.7, 99.5, 99.6 and 99.9% sequence similarities to Pseudomonas beteli, Advenella kasmirensis, Pseudomonas beteli, Providencia stuartii and Bacillus tequilensis, respectively. Further, developed lignite and compost based and clay pellet formulation for facultative chemolithoautotrophic sulfur oxidizing bacteria. Yet, plant inoculations studies should be carried out for isolated sulfur oxidizing bacteria from this study before recommended to the farmers.