ABSTRACT
The early genetic research on lactic acid bacteria (LAB) was dominated by studies on plasmid-associated phenomena, especially in lactococci. Historically, LAB have been clustered into three groups on the basis of sugars metabolism: the obligately homofermentative, the facultative heterofermentative, and the obligately heterofermentative. Oenococcus oeni is a very peculiar LAB, able to survive and proliferate in a hydro-alcoholic solution such as wine. LAB have been isolated from a wide range of environmental niches such as plants, soil, dairy environment, meat, intestinal and urogenital tracts of warm-blooded animals, insects, and so on. Rapid advancement and progress in the comprehension of the genetic basis of industrially relevant traits of LAB make it quite impossible to provide a comprehensive update of this ever changing field. The majority of LAB-associated plasmids belong to the standard type of covalently closed circular, autonomously replicating deoxyribonucleic acid molecules replicating by two basic mechanisms: the rolling circle type of replication or the so-called theta replication.
