earticle

영어

To develop sustainable, low-input but highly productive agricultural practices for better management of soil resources, to combat climate change by reducing the input of energy-intensive chemical fertilizers in Indian soils and resultantly improve soil quality, a sustainable biofertilizer technology is required to facilitate product delivery to enhance crop productivity. Fluorescent pseudomonad strain R81 is a root colonizing rhizobacterium which has a growth- promoting effect on many plants. The PGPR produced a hydroxamate-type siderophore that chelates iron and makes it available to the plant roots and 2, 4- diacetylphloroglucinol (DAPG), an antibiotic that suppresses fungal pathogens. The presence of the siderophore and DAPG in the bioinoculants formulations was found to limit the presence of natural contaminants in non-sterile carriers to acceptable limits, thereby obviating the need of normally-used costly three-time sterilization of the carriers. The purpose of the work was, therefore, to develop suitable culture strategies which can be easily applied at an industrial scale. Accordingly, both a simple batch and a more productive fed-batch culture strategy were developed for mass production of the pseudomonad. In batch procedure, splitting of nitrogen source to NH4Cl and urea had a stabilizing effect on pH which obviated the need of pH control during cultivation. During batch cultivation of the strain in a bioreactor, a maximum of 5 g/L of dry cell mass was achieved when glycerol was 15 g/L and C/N ratio was maintained at 12.5. At higher concentrations of glycerol the biomass yield was lowered due to substrate inhibition. Therefore, the cultivation of the strain was carried out in fed-batch mode with the objective to produce increased biomass, siderophore, and DAPG. LabVIEW software- based computer controlled system was established which achieved flexible and automatic monitoring and control of process parameters. Open loop feeding strategy such as exponential feeding of nutrients and closed loop feedback strategies using dissolved oxygen and pH signals were used in a bioreactor for fed-batch cultivation of the pseudomonad for maximal production of cell mass and DAPG. Compared to batch culture which produced viable cell counts of the order of 5.0 x 109 cfu/ml in a run, the fed-batch culture using pH-based signals produced about 2.7 x 1011cfu/ml, thereby significantly enhancing the productivity of the process by about 50 times. The harvested culture broth was used for preparing a bio-inoculant formulation. The effectiveness of the application of the PGPR formulation has been demonstrated for wheat (Triticum aestivum) crop.