Properties of polysaccharide produced by Azotobacter vinelandii cultured on 4-hydroxybenzoic acid M.C. Vargas-Garcia, M.J. Lopez, M.A. Elorrieta, F. Suarez and J. Moreno Departamento de Biologia Aplicada, Escuela Politecnica Superior, Universidad de Almeria, Almeria, Spain 2002/181: received 8 May 2002, revised 21 October 2002 and accepted 29 October 2002 ABSTRACT M.C. VARGAS-GARCIA, M.J. LOPEZ, M.A. ELORRIETA, F. SUAREZ AND J. MORENO. 2003. Aims: Characterization of the exopolysaccharide produced by Azotobacter vinelandii grown on 4-hydroxybenzoic acid (EPS I), and the comparison between this exopolysaccharide and commercial alginate, constituted the main objective of this work. Methods and Results: Total carbohydrates, uronic acids, acetyl and pyruvyl groups and proteins were determined by colorimetric methods and composition was confirmed by Nuclear Magnetic Resonance studies. Rheological properties were analysed under different physical and chemical conditions. Results showed differences between EPS I and commercial alginate, in relation to both composition and viscosity. Higher amount of guluronnosyl residues were found in EPS I, whereas commercial alginate contained the same proportion of mannuronosyl and guluronnosyl residues. In accordance with this result, EPS I gave rise to solutions of higher viscosity than commercial alginate, although solutions of this polysaccharide showed greater stability when conditions were altered. Conclusions: The exopolysaccharide produced by A. vinelandii grown on 4-hydroxybenzoic acid showed a different composition in comparison with commercial alginate, which leads to higher viscosity values for the aqueous solutions of EPS I. Significance and Impact of Study: This work describes for the first time the characteristics of an exopolysaccharide produced by A. vinelandii from 4-hydroxybenzoic acid, a substrate rarely used as sole carbon source. Keywords: Azotobacter vinelandii, 4-hydroxybenzoic acid, exopolysaccharide, chemical characterization, rheological properties. INTRODUCTION Azotobacter vinelandii is a bacterium with a broad metabolic diversity. This feature enables it to degrade numerous highly recalcitrant substrates (Chan 1986; Wu et al. 1987; Moreno et al. 1990) or to synthesize different compounds (Jones and Greaves 1943; Gonzalez-Lopez et al. 1983, 1986, Revillas et al. 2000), some of which are of commercial interest. Exopolysaccharides (EPS) belong to this group because of their capacity for altering the rheological properties of aqueous solutions (Jarman et al. 1978). Alginate is the most important polysaccharide produced by A. vinelandii (Gorin and Spencer 1966), although other EPS, with sugars as main components, have been obtained from this microorganism (Gorin and Spencer 1966; Vermani et al. 1996). Alginate from A. vinelandii consists of two acids, ß-D-mannuronic and a-L-guluronic acid, and acetyl groups, which can only appear on mannuronosyl residues (Davidson et al. 1977; Skja ˚k-BræK et al. 1986). Length of acid blocks and degree of acetylation, and therefore physicochemical and rheological properties (Smidsrød and Draget 1996), Correspondence to: M.C. Vargas-Garcia, Unidad de Microbiologia, Departamento de Biologia Aplicada, Escuela Politecnica Superior, Universidad de Almeria, 04120 Almeria, Spain. ª 2003 The Society for Applied Microbiology Journal of Applied Microbiology 2003, 94, 388–395