Complete sequence of plasmid pLH1 from Lactobacillus helveticus ATCC15009:Analysis reveals the presence of regions homologous to other native plasmids from the host strain

The complete sequence for plasmid pLH1 from Lactobacillus helveticus ATCC15 009 has been determined. Analysis of the 19,360-bp primary sequence reveale d a putative replication origin and initiation protein, information that co uld provide the basis for the construction of cloning vectors for L. helvet icus. Evidence that pLH1 is theta-replicating could be deduced from the pla smid size, from the homology to the replication protein of the Bacillus nat to theta-replicating plasmid pLS32, and from the identification of a putati ve resolvase gene (orf-195). Although 14 open reading frames capable of enc oding polypeptides longer than 100 amino acids were identified, none, on th e basis of homology with known sequences, appeared to encode a well-charact erized trait relevant to milk fermentation. Plasmid pLH1 revealed regions o f identity with the smaller cryptic plasmids (pLH2 and pLH3) from the same strain and with other tracts of DNA, including insertion sequence elements, from a variety of other lactic acid bacteria. The presence of such regions provides a basis for developing an explanation of the phenotypic variabili ty observed in these bacteria. The plasmid also appears to possess a number of genetic elements present in other lactic acid bacterial plasmids, conse rvation of which would be consistent with an important functional or evolut ionary role. It could be argued that the plasmid complement of L. helveticu s ATCC15009 consists of parasitic entities concerned only with their own re plication and survival, (C) 1999 Academic Press.