ABSTRACT
Plasmid biology is fast becoming an important area of research in bacterial strains used for milk, meat, and plant fermentation processes, as well as for probiotics. Plasmids are defined as autonomous replicating extrachromosomal genetic elements within the bacterial cell. When the cell divides, each daughter cell receives a copy of the chromosomal DNA along with a copy or copies of the plasmids in the parent cell. The presence of a 10 Mdal plasmid in strain KH but not in the majority of the examined variants provided physical evidence implicating involvement of plasmids in Restriction-Modification systems among lactic streptococci. This plasmid linkage provides a genetic mechanism to explain the rapid development of phage-sensitive starter cultures. Clearly, the study of plasmid biology in dairy and food starter cultures has become a prerequisite for future strain improvement programs.
