Annals of Microbiology, 59 (1) 141-144 (2009) Extracellular polysaccharide production by Rhizobium ciceri from Turkey Çiğdem KÜÇÜK 1 *, Merih KIVANÇ 2 1 Harran University, Faculty of Arts and Science, Department of Biology, Şanliurfa; 2 Anadolu University, Faculty of Science, Department of Biology, 26470 Eskisehir, Turkey Received 10 October 2008 / Accepted 9 February 2009 Abstract - The ability of the Rhizobium ciceri, to produce extracellular polysaccharides (EPS) was investigated. Tested carbon and nitrogen sources influced EPS synthesis when R. ciceri Rc5 was grown in a chemically defined medium. Mannitol was the most efficient carbon source among the six sources tested (sucrose, glucose, arabinose, fructose, xylose and rhamnose) and sodium nitrate was the most efficient nitrogen source among the two tested (ammonium sulphate and glycine). High amounts of EPS (1182.0 and 1015 μg ml -1 , respectively) were produced by the Rc5 strain in mannitol and sodium nitrate respectively, which was accompanied by a great increase in the production compared to the control. Key words: Rhizobium ciceri; strain; exopolysaccharide; carbon and nitrogen source. Bacteria of the genus Rhizobium form a symbiotic nitrogen fixing association with plants in the family leguminosae (Becker and Pühler, 1998). This is a selective interaction, since of plant genera which they can infect and in which they can establish a nitrogen fixing symbiosis (Putnoky et al., 1990; Hirsh, 1999). Rhizobia characteristically synthesize copious amounts of extracellular polysaccharides (Kondorosi, 1998; Datta and Basu, 1999). The notion that Rhizobium exopolysaccharides (EPS) participate in the inital stages of recognition leading to host legume nodulation through interaction with lectins in root hairs (Leigh and Coplin, 1992; Hirsh, 1999; Ghosh et al., 2005) is currenlty a subject of active investigation in many researches. For the cells, EPS are thought to play a role in protection against desiccation, toxic compounds, bacteriophages, osmotic stress and to permit adhe- sion to solid surfaces and biofilm formation (Cunningham and Munns, 1984; Hirsh, 1999). Rhizobial EPS are though to play a role in determinating the host plant specificity of nodulation (Zevenhuizen, 1986; Battisti et al., 1992). EPS characteristics and amounts can be influenced by several factors such as composition of the carbon and nitrogen sources as well as incubation conditions (Duta et al., 2004, 2006). In this work we have studied extracellular polysaccharide production by the Rhizobium ciceri Turkish strains and the effect of some sour- ces on production of this substance. Carbon and nitrogen source assays were carried out in 400 ml of chemically defined medium (0.05% yeast extract, 1% man- nitol and 0.01% CaCI 2 2H 2 O, pH 7) (Dudman, 1964). Bacteria were grown (10 8 CFU ml -1 ) in chemically defined medium con- taining 10 mM of either sucrose, glucose, arabinose, mannitol, fructose, xylose, rhamnose and containing 0.1% of either gly- cine, ammonium sulphate, sodium nitrate. Carbon and nitrogen sources was separately sterilized and added to the medium later. The effect of different carbon sources was also studied into the chemically defined medium omitting mannitol. The effect of different nitrogen sources was also studied into the chemically defined medium omitting yeast extract. Production of EPS was make according to Cunningham and Munns (1984) and Becker and Pühler (1998). A Haeker VT02 model viscometer was used to determine viscosity of strains in different source in growth medium. The pH of the samples was determined using a pH meter. Modifications of agitation (50, 100, 150 and 200 rpm) and pH (5, 6, 7, 8 and 9 pH) were also made (Fig. 1) to study the influence of culture conditions on polysaccharide production. Analysis of variance was obtained following the methods of Düzgüneş et al. (1987). Preliminary experiments were performed in order to deter- mine in the incubation time for optimum recovery of EPSs in Rhizobium ciceri strains. Samples were removed at intervals and quantitative extraction of EPS was carried out. According to these results (data not shown), maximum EPS recovery was obtained in 8 day old cultures, so this incubation period was selected for EPS production in further experiments. The forma- tion of polysaccharide was observed in 18 Turkish Rhizobium ciceri strains (Table 1). The results show that the viscosity of the polysaccharide varied from one strain the next. In Rhizobium Rc5 both the yield and the viscosity were the highest. For this reason, Rhizobium Rc5 was selected as the most favorable stra- in to carry out all subsequent experiments of this investigation (Table 1). * Corresponding Author. Phone: +90 414 3440020-1373; E-mail: cdmkucuk@yahoo.com