Extrachromosomal Elements in Group N Streptococci

Abstract

The deoxyribonucleic acid (DNA) of Streptococcus lactis C2, S. cremoris B1, and S. diacetilactis 18-16 was labeled by growing cells in Trypticase soy broth containing 3H-labeled thymine. The cells were gently lysed with lysozyme, ethylenediaminetetraacetic acid, and sodium lauryl sulfate. The chromosomal DNA was separated from plasmid DNA by precipitation with 1.0 M sodium chloride. The existence of covalently closed circular DNA in the three organisms was shown by cesium chloride-ethidium bromide equilibrium density gradient centrifugation of the cleared lysate material. In an attempt to correlate the loss of lactose metabolism with the loss of plasmid DNA, lactose-negative mutants of these organisms were examined for the presence of extrachromosomal particles. Covalently closed circular DNA was detected in the lactose-negative mutants of S. lactis C2 and S. diacetilactis 18-16. In S. cremoris B1, however, no covalently closed circular DNA was observed by using cesium chloride-ethidium bromide gradients. Electron micrographs of the satellite band material from S. lactis C2 and its lactose-negative mutant confirmed the presence of plasmid DNA. Three distinct plasmids having approximate molecular weights of 1.3 x 106, 2.1 x 106, and 5.1 x 10' were observed in both organisms.

TheLactococcus lactisplasmidome: much learnt, yet still lots to discover

“…The ability to rapidly ferment lactose, a typical feature of LAB, is a plasmid-encoded and well-defined characteristic amongst dairy-associated lactococci (Cords et al, 1974). The genes encoding lactose acquisition and utilisation are located in a single operon, lacABCDFEGX, which is regulated by the repressor LacRii encoded by the divergently oriented lacRii gene.…”

A general method for cell lysis and preparation of deoxyribonucleic acid from streptococci

“…Another effect of 1 M NaC1 is precipitation of linear DNA, particularly at low temperatures, e.g. at 0°C [12,13]. This approach for elimination of chromosomal DNA was successful also in S.pyogenes P1800 (Fig.…”

“…Alternatively, NaC1 (final concentration 1-5 M) can be included in the lysis mixture. The salt also helps to purify plasmid DNA since chromosomal (linear) DNA is precipitated [12,13] (see above).…”

Involvement of plasmids in lactose metabolism in Lactobacillus casei suggested by genetic experiments

“…An indispensable property of lactic acid bacteria used in the dairy industry is their ability to ferment lactose. The instability of lactose metabolism in lactic streptococci is well known [1][2][3]. Recently, evidence was presented that the lactose-fermenting ability in Streptococcus lactis is plasmid linked [4,5 ].…”