Inside the Institut Pasteur — Part I Prophage and the Fertility Factor F

Abstract

The Institut Pasteur in Paris, located at the very same premises since it was founded by its namesake in 1888, was originally meant to produce immunizing sera and consequently developed a long and sound tradition in medical bacteriology and virology. Through the latter, the institute was a venue for phage research of the pre-Delbrück era. It was Felix d’Hérelle, a French-Canadian researcher at the Institut Pasteur, who described what he called in 1917 bacteriophages which he isolated from the stools of patients convalescing from shigellosis disentery. Accordingly, d’Hérelle is considered to be one of the discoverers of phages. Although the British Frederick Twort had, already in 1915, observed a bacteria-killing, self-reproducing agent in culture plates with staphyloccoci, this was not known to d’Hérelle. Expert opinions diverge on to whom the merit of priority should go. While Twort’s work ended abruptly with his death as a soldier during the First World War, d’Hérelle left a row of followers who proceeded to describe a series of different phenomena related to phages, but never succeeded in really interpreting their observations. Years later, the husband-and-wife team of Eugène and Elisabeth Wollman, also working at the Institut Pasteur, noticed a remarkable phenomenon: under certain circumstances, some phages would infect bacteria without causing their disintegration. Such phages faded from immediate detection, but each cell from the resulting clone stayed under the constant threat, albeit with low probability, of lysing after some generations, liberating progeny phages in the process. This was the phenomenon called lysogeny. Aside from the virulent phages which caused, unconditionally, the infected bacteria to lyse, there existed, apparently, another category of phages called temperate, which were able to enter the host, and then establish and maintain with it a state of nonlethal equilibrium for many generations. These viral entities — nowadays called provirus or prophages — divided synchronously with the host for many cell cycles, retaining nevertheless the capability of initiating a full-blown lytic cycle. Lysogenic bacteria, i.e. those harboring a prophage, live under the Damoclean sword of the all-time imminent, although rarely spontaneously occurring, death by lysis.