From DNA sequence to application: possibilities and complications

The development of sophisticated genetic tools during the past 15 years hav e facilitated a tremendous increase of fundamental and application-oriented knowledge of lactic acid bacteria (LAB) and their bacteriophages. This kno wledge relates both to the assignments of open reading frames (ORF's) and t he function of non-coding DNA sequences. Comparison of the complete nucleot ide sequences of several LAB bacteriophages has revealed that their chromos omes have a fixed, modular structure, each module having a set of genes inv olved in a specific phase of the bacteriophage life cycle. LAB bacteriophag e genes and DNA sequences have been used for the construction of temperatur e-inducible gene expression systems, gene-integration systems, and bacterio phage defence systems. The function of several LAB open reading frames and transcriptional units h ave been identified and characterized in detail. Many of these could find p ractical applications, such as induced lysis of LAB to enhance cheese ripen ing and re-routing of carbon fluxes for the production of a specific amino acid enantiomer. More knowledge has also become available concerning the fu nction and structure of non-coding DNA positioned at or in the vicinity of promoters. In several cases the mRNA produced from this DNA contains a tran scriptional terminator-antiterminator pair, in which the antiterminator can be stabilized either by uncharged tRNA or by interaction with a regulatory protein, thus preventing formation of the terminator so that mRNA elongati on can proceed. Evidence has accumulated showing that also in LAB carbon ca tabolite repression in LAB is mediated by specific DNA elements in the vici nity of promoters governing the transcription of catabolic operons. Although some biological barriers have yet to be solved, the vast body of s cientific information presently available allows the construction of tailor -made genetically modified LAB. Today, it appears that societal constraints rather than biological hurdles impede the use of genetically modified LAB.