Genetics of mesophilic citrate fermenting lactic acid bacteria.

A prerequisite for the stabilization of important features, such as aroma production, in starter strains used in dairy fermentations, is an extensive knowledge of the genetic basis of these properties. In this thesis the genetic basis of citrate metabolism in Lactococcus lactis subsp. lactis var. diacetylactis and Leuconostoc spp. are studied and genetic aspects of citrate-fermenting Leuconostoc strains are analyzed.- Chapter II describes the development of a cloning system for Leuconostoc which was necessary due to the lack of natural transformation systems.- Chapter III describes the use of polymerase chain reaction to classify Leuconostoc strains.- Since lactose is the most important carbohydrate used by lactic acid bacteria, knowledge of the genetic basis of the genes involved in lactose metabolism can offer important data concerning gene regulation and expression. Chapters IV and V describe the cloning and expression of the lactose genes of Leuconostoc ssp.- Cloning and functional expression in Escherichia coli of the the citrate permease gene of Lactococcus lactis subsp. lactis var. diacetylactis are described in Chapter VI.- A comparison of the lactococcal citrate permease with the Leuconostoc lactis citrate permease gene is described in Chapter VII.- A summary together with concluding remarks are given in Chapter VIII