PHYSICOCHEMICAL CHARACTERIZATION OF AN ACETAN VARIANT SECRETED BY ACETOBACTER-XYLINUM STRAIN CR1 4/

Chemical mutagenesis has been used to produce mutants of Acetobacter x ylinum NRRL B42 that are cellulose-negative and that produce variants of the acetan structure deficient in the side-chain sugar residues. Th e product of A. xylinum strain CR1/4 has been shown to possess a tetra saccharide repeat unit with the side chain terminating in glucuronic a cid. X-ray diffraction studies of oriented fibres suggest that the pol ysaccharide CR1/4 forms a fivefold helix with a pitch of 4.8 nm. Light -scattering studies on CR1/4 solutions suggest a molecular weight of 1 .2 x 10(6) with radii of gyration values of 86 nm (aqueous solution) a nd 67 nm (0.1 M NaCl solution). The magnitude of the measured radii of gyration and the shape of the Holtzer plots suggest that CR1/4 can be described as a stiff coil. Preliminary differential scanning calorime try data show melting behaviour consistent with order-disorder transit ions of a charged helical structure. Rheological studies have revealed new synergistic interactions of CR1/4 with locust bean gum. Comparati ve studies of acetan and CR1/4 show that decreasing the length of the side chain enhances the solution viscosity.