Global changes in gene expression in Escherichia coli K12 induced by bacteriophage Mu Gem protein.

L'e´tude des proprie´te´s de croissance de souches lysoge´nes Mu par comparaison avec celles de souches non lysoge´nes, nous a permis d'observer que le temps de division en milieu minimal est multiplie´par 4 et plus quand la bacte`rie transporte le prophage portant le ge`negem mute´(Mugem3). Ce phagee`tant déja`connu pour son ro^le dans la modulation de l'expression des ge`nes de l'ho^te, nous avons analyse´les prote´ines extraites des souches lysoge`nes et non lysoge`nes, dosage rapide de l'expression globale des ge`nes. Le profil des prote´ines extraites montre l'existence de variations quantitatives importantes entre celui des souches non lysoge`nes, celui des souches lysoge`nes pour le phage Mu de type sauvage et celui des souches lysoge`nes pour le phage Mugem3. Ces effets ne sont plus aussie`vidents quand les souches croissent en milieu enrichi. Ces changements importants de l'e´tat physiologique des souches lysoge`nesvs. non lysoge`nes, seion les conditions de croissance,e´largissent le concept de lysoge`nie. Durant de nombreuses anne´es le prophage ae´te´conside´re´uniquement comme un facteur potentiellement le´tal ; ici, il apparai^tégalement comme une´le´ment ge´ne´tique capable de modifier profonde´ment la biologie de l'ho^te.

We have studied the growth properties of some Mu lysogens with respect to the non-lysogenic strain and have observed that the division time in minimal medium was increased over 4-fold when the bacteria carried the prophage mutated in thegem gene (Mugem3). Since this phage gene has previously been shown to be involved in modulation of expression of host genes, we have analysed the proteins extracted from lysogens and non-lysogens as a rapid assay of global gene expression. The pattern of proteins extracted showed marked quantitative variations between non-lysogens, lysogens for wild-type Mu and lysogens for phage Mugem3. These effects were no longer as evident when the strains were grown in rich medium. This dramatic change in the physiological state of the lysogenic strain versus the non-lysogenic in particular growth conditions extends the concept of lysogeny. For many years, the prophage has been considered only as a potentially lethal factor, while here it also appears as a genetic element capable of profoundly modifying host biology.