title: Influence of lactococcal plasmid on the specific growth rate of host cells.
abstract: OBJECTIVE
  To investigate a lactococcal plasmid responsible for a reduction in growth rate of its host cell.
  
  
  RESULTS
  Lactococcus lactis subsp. lactis biovar. diacetylactis DRC1 carries a high number of plasmids. The DRC1 wild-type strain was found to grow more slowly than a plasmid-free derivative of DRC1. The plasmids extracted from DRC1 together with an indicator plasmid were cotransformed into the plasmid-free strain DRC1021. A 7.4-kb cryptic plasmid, designated pDR1-1, was found to significantly affect the maximum specific growth rate ( micro max) of the host cell. Polymerase chain reaction (PCR) analysis was carried out in order to detect the presence of pDR1-1 in the other L. lactis strains. The micro max of the single pDR1-1-positive strain was determined to be the same as that of DRC1.
  
  
  CONCLUSIONS
  These results suggest that pDR1-1 (or a pDR1-1-like plasmid) is a critical factor in the reduction of the micro max of DRC1, and that its effect on the micro max is significantly greater than that of any other coexisting plasmid.
authors.affiliation: Department of Animal Products Research, National Institute of Livestock and Grassland Science, Norindanchi, Tsukuba, Japan. mihokoba@affrc.go.jp
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: M
authors.initials: M
authors.lastname: Nomura
authors.forename: Y
authors.initials: Y
authors.lastname: Fujita
authors.forename: T
authors.initials: T
authors.lastname: Okamoto
authors.forename: S
authors.initials: S
authors.lastname: Ohmomo
mesh_terms: D005285:Fermentation / Q000235:genetics; D013294:Lactococcus lactis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D010957:Plasmids / Q000032:analysis / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors