DEVELOPMENT OF A GROWTH-MEDIUM SUITABLE FOR EXOPOLYSACCHARIDE PRODUCTION BY LACTOBACILLUS-DELBRUECKII SSP. BULGARICUS RR

Complex media are commonly used in studies examining exopolysaccharide production by Lactobacillus delbrueckii ssp. bulgaricus. However, qua ntification of exopolysaccharide in complex medium can be complicated by interference due to carbohydrate polymers contained in media compon ents. This study was undertaken to identify components of MRS, a commo n medium for cultivation of L. delbrueckii ssp. bulgaricus, that inter fere with exopolysaccharide quantification, to develop a medium for pr oduction of exopolysaccharide that provides for growth of L. delbrueck ii ssp. bulgaricus strain RR similar to MRS, and to demonstrate exopol ysaccharide production by L. delbrueckii ssp. bulgaricus RR grown in t he newly developed medium. Phenol-sulfuric acid determinations were co nducted on uninoculated MRS broth with and without yeast extract, beef extract and proteose peptone #3. These three ingredients accounted fo r 94% of the total background exopolysaccharide-equivalent in MRS brot h. Based on these results, a semi-defined medium (SDM) providing minim al interference was developed using yeast nitrogen base (R) and Bacto casitone (R). Growth of L. delbrueckii ssp. bulgaricus RR at 42 degree s C in semi-defined medium and MRS was evaluated, and generation times did not differ significantly (0.94 h in MRS and 0.85 h in SDM). Exopo lysaccharide production by L. delbrueckii ssp. bulgaricus RR during gr owth in semi-defined medium was evaluated at 30 and 40 degrees C. The rate of exopolysaccharide production was lower at 30 degrees C (8.04 ( mg/l-h) than at 40 degrees C (11.95 (mg/l-h), but the maximal concentr ation of exopolysaccharide produced was similar at both temperatures. (C) 1998 Elsevier Science B.V.