157 KHON KAEN AGR. J. 42 SUPPL. 4 : (2014). 1 Program in Biology, Faculty of Science, Udon Thani Rajabhat University, Udon Thani, 41000, Thailand * Corresponding author: kingchanchoomponla@yahoomail.com Isolation and characterization of Rhizobium spp. from root of legume plants species Kingchan Malisorn 1* and Chidkamon Prasarn 1 ABSTRACT: Isolation and Characterization of Rhizobium sp. were collected from root nodules of legume plants in subfamily Mimosoideae, Caesalpiniodeae and Papilionoideae. One hundred thirteen strains were characterized by biochemical assay. Morphological properties of Eighty six isolates were fast growing indicated that isolated rhizobia and had color of colony in white and pink. There were produced gummy colonies on YMCA plates after 3 days of incubation at 37 o C. All strains were rod shaped, gram-negative and capable of producing poly hydroxyl butyrate. All strains utilized glucose, manitol, lactose as fermentation sugar. The isolates from present study may be useful to increase the symbiotic nitrogen fxation in legume plants Keywords: isolation, characterization, Rhizobium, legume plant Introduction Nutrient enrichment of soils by nitrogen fxing symbiotic bacteria present in legumes has been known for centuries. Scientifc demonstration of this symbiosis was started in 19 th century and it established the facts that bacteria present in nodules on legume roots are responsible for fxing atmospheric nitrogen (Deshwal etal., 2011). Rhi- zobium species are known as bacteria that act as the primary symbiotic fxer of nitrogen. These bacteria infect the roots of leguminous plants, leading to the formation of lumps or nodules where the nitrogen fxation takes place. The bacterium’s enzyme system supplies a constant source of reduced nitrogen to the host plant and the plant furnishes nutrients and energy for the activities of the bacterium. This symbiosis reduces the requirements for nitrogenous fertilizers during the growth of leguminous crops (Zsbrau, 1999). Rhizobium species are symbiotically associated with several leguminous plants such as Pisum sativam, Glycine max, Alfa alfa etc. These Rhizo- bium are Gram negative, motile, and non-endo- spore forming bacteria. These bacteria are gener- ally cultured in Yeast Mannitol Agar medium (YEMA medium) (Holt et al., 1994). Rhizobium species give colorless gummy appearance when grown on YEMA medium supplemented with congo red. The gummy appearance is because of extracellular polysaccharide production. Importantly, they are able to accumulate a high amount of poly hydroxyl butyrate (PHB) intracel- lular (Kumari and Dhingra, 2013). Rhizobiaceae family contains six genera namely Rhizobium, Sinorhizobium, Mesorhizobium, Allorhizobium, Azorhizobium and Bradyrhizobium, respectively (Okazaki et al., 2004). Biofertilizer promotes plant growth and productivity has internationally been accepted as an alternative source of chemical fertilizer. Rhizobacteria effectively colonize plant root and increase plant growth by production of