A mutant strain of Beijerinckia indica L3 screened by a traditional chemical mutagenesis was grown in lactose-based mineral salts medium (MSM) for the production of heteropolysaccharide-7 (PS-7). The beta-galactosidase was expressed constitutively in the mutant and its activity was higher than that in parent strain. The highest amount of PS-7 produced by the mutant was 2.88 g/L with a viscosity of 4530 cP in lactose-based MSM medium. The PS-7 production was enhanced by the addition of 4 a glucose into lactose-based MSM mediurn, reaching 5.52 g/L with a viscosity of 39531 cP. PS-7 of 6.18 g/L with a viscosity of 45772 cP was produced from the mutant grown in whey medium. The PS-7 production from the mutant reached 7.04 g/L when 4 g/L glucose was added to the whey medium. Compositional analysis of PS-7 produced by the mutant grown in whey mediurn or lactose-based mineral salts medium showed that the ratios of glucose/rhamnose were maintained in the range similar to that of parent strain, indicating the same compositional structures of PS-7. (c) 2005 Elsevier Ltd. All rights reserved.