Enlargement of Escherichia coli after bacteriophage infection. I. Description of the phenomenon

Look Who's Talking: T-Even Phage Lysis Inhibition, the Granddaddy of Virus-Virus Intercellular Communication Research

That communication can occur between virus-infected cells has been appreciated for nearly as long as has virus molecular biology. The original virus communication process specifically was that seen with T-even bacteriophages-phages T2, T4, and T6-resulting in what was labeled as a lysis inhibition. Another proposed virus communication phenomenon, also seen with T-even phages, can be described as a phage-adsorption-induced synchronized lysis-inhibition collapse. Both are mediated by virions that were released from earlier-lysing, phage-infected bacteria. Each may represent ecological responses, in terms of phage lysis timing, to high local densities of phage-infected bacteria, but for lysis inhibition also to locally reduced densities of phage-uninfected bacteria. With lysis inhibition, the outcome is a temporary avoidance of lysis, i.e., a lysis delay, resulting in increased numbers of virions (greater burst size). Synchronized lysis-inhibition collapse, by contrast, is an accelerated lysis which is imposed upon phage-infected bacteria by virions that have been lytically released from other phage-infected bacteria. Here I consider some history of lysis inhibition, its laboratory manifestation, its molecular basis, how it may benefit expressing phages, and its potential ecological role. I discuss as well other, more recently recognized examples of virus-virus intercellular communication.

Experimental examination of bacteriophage latent-period evolution as a response to bacterial availability

For obligately lytic bacteriophage (phage) a trade-off exists between fecundity (burst size) and latent period (a component of generation time). This trade-off occurs because release of phage progeny from infected bacteria coincides with destruction of the machinery necessary to produce more phage progeny. Here we employ phage mutants to explore issues of phage latent-period evolution as a function of the density of phage-susceptible bacteria. Theory suggests that higher bacterial densities should select for shorter phage latent periods. Consistently, we have found that higher host densities (>/== approximately 10(7) bacteria/ml) can enrich stocks of phage RB69 for variants that display shorter latent periods than the wild type. One such variant, dubbed sta5, displays a latent period that is approximately 70 to 80% of that of the wild type-which is nearly as short as the RB69 eclipse period-and which has a corresponding burst size that is approximately 30% of that of the wild type. We show that at higher host densities (>/== approximately 10(7) bacteria/ml) the sta5 phage can outcompete the RB69 wild type, though only under conditions of direct (same-culture) competition. We interpret this advantage as corresponding to slightly faster sta5 population growth, resulting in multifold increases in mutant frequency during same-culture growth. The sta5 advantage is lost, however, given indirect (different-culture) competition between the wild type and mutant or given same-culture competition but at lower densities of phage-susceptible bacteria (</= approximately 10(6) bacteria/ml). From these observations we suggest that phage displaying very short latent periods may be viewed as specialists for propagation when bacteria within cultures are highly prevalent and transmission between cultures is easily accomplished.

Enlargement of Escherichia coli after bacteriophage infection. II. Proposed mechanism

Division of Escherichia coli was stopped and mean cellular volume was increased after infection with T-even phage. This host cell enlargement was temperature-dependent, cyanide-sensitive, and stable in the presence of hypertonic medium. Enlargement ceased at about the same time that energy metabolism ceased. Initially, enlargement was accompanied by a decrease in mean cell density. Tritiated 2, 6-diaminopimelic acid was accumulated and incorporated into cold acid-insoluble material at the preinfection rate. These findings suggest that the effect on host cell size is only in part an osmotic phenomenon and that it also reflects continued growth of the surface of the infected cell in the absence of cell division.