This invention involves the production of heteropolysaccharides such as xanthan gum by the continuous fermentation of suitable nutrient media with new degenerative resistant variants of Xanthomanas campestris. Fermentation is conducted in a nitrogen, sulfur or phosphorous limited nutrient medium containing glucose or a minimal medium plus yeast extract and glutamic acid, in a first fermenter to enhance cultural growth. After the limiting growth element (nitrogen, sulfur or phosphorous) has been essentially consumed, the medium is then transferred to a second fermenter and fermentation continued while adding a suitable carbohydrate which the bacteria convert into the heteropolysaccharide product. The process may be modified by carrying out cultural growth and production of the polysaccharide in the same fermenter. The bacteria employed were cultured from a glucose-mineral salts medium fortified with yeast extract or a glucose-defined minimal medium in which ammonium chloride served as the sole assimilable nitrogen source.