Edinburgh Napier University

  The complete sequence for plasmid pLH1 from Lactobacillus helveticus ATCC15009 has been
determined. Analysis of the 19,360-bp primary sequence revealed a putative replication origin and
initiation protein, information that could provide the basis for the construction of cloning vectors for
L. helveticus. Evidence that pLH1 is theta-replicating could be deduced from the plasmid size, from
the homology to the replication protein of the Bacillus natto theta-replicating plasmid pLS32, and
from the identification of a putative resolvase gene (orf-195). Although 14 open reading frames
capable of encoding polypeptides longer than 100 amino acids were identified, none, on the basis of
homology with known sequences, appeared to encode a well-characterized trait relevant to milk
fermentation. Plasmid pLH1 revealed regions of 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 variability observed in these bacteria. The plasmid also
appears to possess a number of genetic elements present in other lactic acid bacterial plasmids,
conservation of which would be consistent with an important functional or evolutionary role. It could
be argued that the plasmid complement of L. helveticus ATCC15009 consists of parasitic entities
concerned only with their own replication and survival.