Composting of rice-residues using lignocellulolytic plant-probiotic Stenotrophomonas maltophilia, and its evaluation for growth enhancement of Oryza sativa L.

Abstract

Rice straw residues, a prominent agricultural waste were converted into bioactive compost by application of plant-probiotic bacterium having lignocellulolytic activity. The isolate was also found to have excellent plant growth promoting attributes. Stenotrophomonas maltophilia RSD6 was isolated from the rhizospheric soil of Oryza sativa L. and was identified on the basis of its phenotypic, physiological features and 16S rRNA sequence analysis. S. maltophilia RSD6 had plant growth stimulating attributes including production of siderophore, indole acetic acid and inorganic phosphate solubilization. Eventually , the isolate also has the potential to degrade lignocellulosic agricultural-waste due to production of enzymes including lignases, xylanase and cellulases, and therefore it was used for composting of rice straw residues. There was increase in nitrogen, phosphorus, and potassium content in mature compost, where final content was recorded as 16.26, 0.072, 18.49 (g/kg) after 90 days. The lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase productions for S. maltophilia RSD6, were found to be, 1.125 units/min/mL, 0.069 units/min/mL and 0.219 CU mL −1 respectively. Endoglucanase, exog-lucanase, cellobiase and xylanase activities were also recorded to be 0.445, 0.174, and 0.709 and 0.240 IU/mL, respectively. The treatments of rice plants with RSD6 showed significant enhancement of shoot and root length and biomass as compared to control. S. maltophilia RSD6 not only improved the growth of rice plants but also has the potential to degrade lignocel-lulosic waste because of its rapid compost traits. Therefore, RSD6 was utilized for management of rice straw residues in an eco-friendly manner, resulting in compost that was having plant probiotic characteristics due to presence of RSD6, and it may be used as an alternative to agrochemicals.