Interaction of prophages and colicin Ib at the single cell and population-wide level

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Colicins are bacteriocins produced by and toxic for E. coli and close relatives. Colicins are regarded as classical example of division or labor in clonal bacterial populations. They serve as public good for the population of producers but are synthesized by only a fraction of the population, which die upon colicin release. We studied the regulation of colicin Ib (ColIb), produced by a human pathogenic Salmonella enterica sv. Typhimurium strain (S. Tm) at the single cell level using gfp-reporters. We confirmed that ColIb is under certain conditions made by a fraction of the population which, at least in part lyse and release ColIb. By then, the release mechanism for ColIb was unknown. Specific lysins, as they are known for other colicins, are absent in the case of ColIb. Our work in the first funding period of this Priority Programme established a new link between temperate, lambdoid phages and ColIb. We show that the presence of different lambdoid prophages or their lysis genes correlates with increased ColIb release into the S. Tm culture supernatant. This suggests that ColIb, which lacks its own specific lysin, can parasitize lysis genes of temperate phages to be released in the environment. In the second funding period, we now aim to further investigate the significance of temperate phages for colicin biology at the single cell level as well as for bacterial fitness and evolution of colicin production as cooperative trait. Generating the appropriate S. Tm mutant- and reporter-strains we pursue the following objectives. First, we will investigate if other colicins besides ColIb are also released in the course of phage-mediated host lysis. Second, we assume that the prophage(s) will be preferentially activated within the same subset of ColIb (cib)-expressing S. Tm. Thereby, this part of the cib-expressing bacteria lyses in order to release ColIb. We will test this idea by analysing ColIb (cib)-expression and activation of temperate lambdoid phages at the single cell level using fluorescent protein reporters, microfluidics and real-time microscopy. Lastly we will focus on modeling the tripartite interaction of host bacteria, colicins and temperate phages and test if whether this is an evolutionary stable strategy. To this end, we will use by a combination of in vitro experiments and mathematical modeling.