Bacteriophages of Lactic Acid Bacteria

Abstract

Bacteriophages of mesophilic and thermophilic lactic streptococci and Lactobacilli have been the subject of numerous investigations. The most extensive studies have been carried out on phages of mesophilic lactic streptococci. Phages have been differentiated on the basis of morphology, serology, and DNA characterization. Morphologically distinct phages belong to different DNA homology groups, related phages being found in such widely separated locations as Ireland, Germany, and New Zealand. Surveys of thermophilic lactic streptococcal phages to date have indicated that the majority of phages belong to one morphological type. Lactobacillus phages belong to several morphological groups, including phages with contractile and noncontractile tails.The role of lysogenic strains of lactic acid bacteria as a source of lytic phages is unclear. In general, lytic and temperate phages of lactic streptococci are not closely related by DNA homology. However, some DNA homology groups contain both temperate and lytic phages, suggesting that these phages may have a common ancestor. Heteroduplex DNA studies indicated that in some instances, lytic phages evolve from one another, but it is possible that DNA from temperate phages contributes to the evolution of phage. DNA studies on Lactobacillus phages have shown a closer relationship between temperate and lytic phages.A number of recent studies have provided restriction endonuclease maps of phage genomes. Several genes, such as structural genes, and sites for attachment and packaging initiation in temperate phage DNA, have been located. Extensive genetic studies of lactic phages are required to elucidate relationships between phage and host, particularly as they relate to phage resistance in lactic acid bacteria.