Thennakoon, G.G.C.G.Jayalal, R.G.U.Kulasooriya, S.A.2025-11-102025-11-102021-11-11Proceedings of Peradeniya University International Research Sessions (iPURSE) - 2021, University of Peradeniya, P 117978-624-5709-07-6https://ir.lib.pdn.ac.lk/handle/20.500.14444/6331Rhizobia are naturally occurring soil bacteria, of them plant growth-promoting Rhizobacteria (PGPR) have an ability to fix atmospheric inert nitrogen into plant utilizable forms like ammonia and amino acids. They accomplish biological nitrogen fixation through symbiotic associations with legume plants. In the present study, Rhizobia strains isolated from soybean (Glycine max), groundnut (Arachis hypogaea), mung bean (Vigna radiata), cowpea (Vigna unguiculata), common bean (Phaseolus vulgaris), and white clover (Trifolium repens) were purified and characterized morphologically, biochemically and physiologically. According to morphological characterizations, Rhizobia were found to be gram-negative and rod-shaped/ roughly rounded bacteria. The colony appearance was gummy, white, opaque, or immersed. Biochemical characteristics were tested against five different antibiotics (Tetracycline, Cloxacillin, Ampicillin, Ciprofloxacin, and Metronidazole), five different amino acids (L-tryptophan, Urea, Glycine, Cysteine, and L-tyrosine) and six different carbohydrates (D-glucose, Galactose, Fructose, Lactose, Mannitol, and Sucrose). Tetracycline was given solitary observation for the resistance of selected strains. Sucrose and dextrose were optimally utilized by Rhizobia besides mannitol. Utilization of amino acids by many strains was restricted to Cysteine and L-tyrosine. Green gram and cowpea strains were fast growers with acid-production in BTB and BRYMA. Similar results were obtained in UV absorbance of Rhizobial culture densities at 254 nm wavelength for their growth rate. Following the physiological characteristics, many strains were restricted to the 6.5-9.5 pH range and 0.5% -1% salinity levels. There was optimized growth of all strains at 32 0C and 35 0C temperatures incubation. Groundnut, cowpea, and green gram obtained excellent potential to nodulation out of other Rhizobia inoculated legumes with authentication. The study implies the importance of selecting the most effective and efficient Rhizobial strain for a particular physical and biochemical conditions of the host plant and rhizosphere. The recorded properties potential to implement sustainable agriculture by promoting them as biofertilizers to replace chemical N fertilizer.en-USRhizobium Spp.Rhizobium characterizationAuthentication of RhizobiaNodulationNitrogen fixationArticle