Plasmid DNA from lactic streptococci was subjected to electrophoresis on agarose gels. The plasmid profiles so obtained were strain specific and sufficiently stable to suggest their use in strain differentiation. A group of Streptococcus lactis strains, 712. 763 (ML3), 505 (C2) and 2031 (C2), found to have similar plasmid profiles, were shown to be closely related. Gene transfer by transduction and conjugation occurred between members of this group at frequencies comparable to those in homologous systems and temperate phages cross plated readily between their prophage cured derivatives. Minor variations were, however, found between these four strains; slight differences in plasmid profiles, lysogenic status, prophage curability and temperate phage morphology were detected and it is suggested that these have evolved as a result of maintenance in different environments.

A gene for the lysin of Lactococcus lactis bacteriphage phi vML3 was cloned using an Escherichia coli/bacteriophage lambda host-vector system. The gene was detected by its expression of antimicrobial activity against L. lactis cells in a bioassay. The cloned fragment was analysed by sub-cloning on to E. coli plasmid vectors and by restriction endonuclease and deletion mapping. Its entire DNA sequence was determined and an open reading frame for the lysin structural gene was identified. The sequenced lysin gene would express a protein of 187 amino acids with a molecular weight of 21,090, which is in good agreement with that of a protein detected after in vitro transcription and translation of DNA encoding the gene. Expression of the lysin gene in E. coli and B. subtilis from an adjacent bacteriophage promoter was readily detected but in L. lactis expression of lysin was found to be lethal. The bacteriophage phi vML3 lysin had sequence homology with protein 15 of B. subtilis bacteriophage PZA. This protein is involved in DNA packaging during bacteriophage maturation rather than in host cell lysis. The cloning and analysis of the phi vML3 lysin gene is of importance in further understanding lactic streptococcal bacteriophages, for the development of positive selection vectors and for biotechnological applications of relevance to the dairy industry.

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Foods produced by genetic engineering technology are now appearing on the market and many more are likely to emerge in the future. The safety aspects, regulation, and labelling of these foods are still contentious issues in most countries and recent surveys highlight consumer concerns about the safety and labelling of genetically modified food. In most countries it is necessary to have approval for the use of genetically manipulated organisms (GMOs) in the production of food. In order to police regulations, a technology to detect such foods is desirable. In addition, a requirement to label approved genetically modified food would necessitate a monitoring system. One solution is to ‘tag’ approved GMOs with some form of biological or genetic marker, permitting the surveillance of foods for the presence of approved products of genetic engineering. While non‐approved GMOs would not be detected by such a surveillance, they might be detected by a screen for DNA sequences common to all or most GMOs. This review focuses on the potential of using common DNA sequences as detection probes for GMOs. The identification of vector sequences, plant transcription terminators, and marker genes by PCR and hybridization techniques is discussed.