Contribution of reutericyclin production to the stable persistence of Lactobacillus reuteri in an industrial sourdough fermentation.

Reutericyclin is a small molecular weight antibiotic produced by the sourdough isolate Lactobacillus reuteri LTH2584. This strain was isolated from an industrial sourdough, SER, in 1988. To determine whether reutericyclin formation contributes to the stable persistence of L. reuteri in sourdough, evaluations were made on whether reutericyclin-producing strains were among L. reuteri isolates from the SER sourdough obtained in 1994 and 1998. These strains were characterised on species and strain level by physiological tests and randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) patterns. Reutericyclin production in dough was evaluated by two methods, a bioassay and HPLC. Throughout 10 years of continuous propagation, reutericyclin-producing L. reuteri strains were present in SER sourdough. All isolates exhibited similar physiological properties and molecular typing revealed closely related patterns. Two isolates obtained in 1994 and 1998 were identical. Reutericyclin produced in situ by L. reuteri was active in dough against reutericyclin-sensitive L. sanfranciscensis. The reutericyclin concentration in dough fermented with L. reuteri was 5 mg kg(-1). The results indicate that reutericyclin production contributed to the stable persistence of L. reuteri in sourdough. Because reutericyclin is produced in active concentrations during sourdough fermentations, it is a suitable candidate for use as natural preservative.