Screening and selection of exopolysaccharide-producing strains of Lactobacillus delbrueckii subsp. bulgaricus

AIMS: The selection of exopolysaccharide (EPS)-producing strains of Lactobacillus delbrueckii subsp. bulgaricus. METHODS AND RESULTS: Improved EPS-overproducing strains of L. delbrueckii subsp. bulgaricus were derived by chemical mutagenesis and selection. Initial screening of the chemically induced mutant pool relied primarily on the selection of strains with raised levels of lactic acid and reduced biomass formation. Supporting selection criteria used were ropiness and colonial mucoidy. Final screening of candidate strains undertaken in a semi-defined medium in batch culture, resulted in the selection of a mutant with a 35% improvement in specific EPS yield relative to the parent strain. CONCLUSIONS: Initial selection of mutants of L. delbrueckii subsp. bulgaricus on the basis of enhanced formation of lactate and reduced biomass formation, coupled with a ropy or mucoid phenotype, proved to be a satisfactory means of isolating strains with the potential for a higher level of specific EPS production than the parent strain. SIGNIFICANCE AND IMPACT OF THE STUDY: The assay protocol allowed for the selection of an EPS-overproducing strain of L. delbrueckii subsp. bulgaricus. Such strains are useful for the purposes of metabolic studies related to EPS-production.