ORIGINAL PAPER Azotobacter vinelandii lacking the Na + -NQR activity: a potential source for producing alginates with improved properties and at high yield Itzel Gayta ´n • Carlos Pen ˜a • Cinthia Nu ´n ˜ez • Marı ´a S. Co ´rdova • Guadalupe Espı ´n • Enrique Galindo Received: 27 February 2012 / Accepted: 17 May 2012 / Published online: 7 June 2012 Ó Springer Science+Business Media B.V. 2012 Abstract The mutant ATCN4 strain of Azotobacter vin- elandii, which lacks the Na ? -NQR activity and results in an alginate overproduction (highly mucoid phenotype), was cultured in shake flasks in minimal and rich medium, and the chemical composition and rheological properties of the alginate were determined. Mutant ATCN4 exhibited a high efficiency for sucrose conversion to alginate and PHB accumulation, reaching yields that were 3.6- and 1.6-fold higher than those obtained from the wildtype cultures in minimal medium (Burk’s sucrose, BS). The alginate pro- duced by ATCN4 in the minimal medium had a high degree of acetylation (C4 %) and a low G/M ratio (=2) with respect to the polymer synthesised in the rich medium (BS with yeast extract) (degree of acetylation = 0 % and G/M ratio of 4.5). The alginate produced in the minimal medium exhibited a pronounced pseudoplastic behaviour and a higher G* module in comparison to that observed in the alginate obtained in the cultures using a rich medium. The ATCN4 mutant culture in the minimal medium pro- moted the synthesis of a polymer of improved rheological quality in terms of its mechanical properties. These char- acteristics make this mutant a valuable source for produc- ing alginates with improved or special properties. Keywords Alginate  A. vinelandii  Na ? -NQR activity  Viscosity  Degree of acetylation Introduction Alginate is a polysaccharide composed of variable amounts of b-D-mannuronic acid and its C5-epimer, the a-L-gulu- ronic acid linked by 1-4 glycosidic bonds. The monomers are distributed in blocks of continuous mannuronate (M) residues, guluronate (G) residues or alternating resi- dues (MG) (Draget and Taylor 2011). These polymers have been used in a wide range of applications, acting as sta- bilising, thickening or gel- or film-forming agents, in var- ious industrial fields (Galindo et al. 2007; Pen ˜a et al. 2011a). Additionally, there are still new applications being discovered, such as their use as a source of soluble fibre or in medical products (Galindo et al. 2007). New applications of the alginates are determined by the chemical composition and the molecular mass of the polymers. For example, it has been shown that alginates with a high proportion of mannuronate residues are able to induce cytokine production and may stimulate Toll-like receptors during the immunological response (Draget and Taylor 2011). In addition, alginate oligoguluronates are able to modify the mucin polymer network structures in the mucus of some organs, which opens new possibilities for the treatment of some respiratory diseases by increasing the mucosal uptake of some drugs or improving their bio- availability, and by decreasing the viscosity of the sputum (Draget and Taylor 2011). It is known that the effectiveness of an alginate as a support for the immobilisation of cells and drugs depends on the molecular mass of the polymer and on the relative content of the two monomers (Her- na ´ndez et al. 2010). I. Gayta ´n  C. Pen ˜a  M. S. Co ´rdova  E. Galindo (&) Departamento de Ingenierı ´a Celular y Biocata ´lisis, Instituto de Biotecnologı ´a, Universidad Nacional Auto ´noma de Me ´xico, Apdo. Post. 510-3, 62250 Cuernavaca, Morelos, Me ´xico e-mail: galindo@ibt.unam.mx C. Nu ´n ˜ez  G. Espı ´n Departamento de Microbiologı ´a Molecular, Instituto de Biotecnologı ´a, Universidad Nacional Auto ´noma de Me ´xico, Apdo. Post. 510-3, 62250 Cuernavaca, Morelos, Me ´xico 123 World J Microbiol Biotechnol (2012) 28:2731–2740 DOI 10.1007/s11274-012-1084-4