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 (>ϳ10 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 ϳ70 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 ϳ30% of that of the wild type. We show that at higher host densities (>ϳ10 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 (<ϳ10 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.Phage serve as important viral predators of bacteria (17,38,39), and the rate that bacteria are phage adsorbed is proportional to phage density (2, 24). Here we consider two factors affecting lytic-phage population growth to higher densities: fecundity and generation time. The fecundity of an individual phage is its per-bacterium burst size. Generation time is less straightforward, consisting of a diffusion-limited extracellular search for bacterial hosts followed by a latent period. The latent period encompasses the active phage infection of an individual bacterium. The extracellular search is the period of inert phage dissemination. A higher host densities-e.g., 10 7 versus 10 5 bacteria/ml-phage populations can grow more rapidly simply because phage can find bacteria faster (7).As originally demonstrated in the classic work of Doermann (15), the truncation of an active phage infection, e.g., as occurs following artificial lysis, reduces the duration of intracellular phage progeny maturation. This truncation results in a decline in a phage's burst size. Various authors nonetheless have theorized that individual phages can achieve faster population growth through latent-period reduction despite the associated reduction in burst size (1,8,11,27,37). This advantage occurs only at higher ...
Bacillus amyloliquefaciens strain H is lysogenic for a large temperate phage we call H2. H2 has a polyhedral head 85 nm in diameter and a tail of about 17 x 434 nm. H2 lysogenizes Bacillus subtilis between the tyrA and metB genes, and gives specialized transduction of metB and, at lower frequencies, of ilvD and ilvA. The phage carries a thymidylate synthase gene and converts thymine auxotrophs of B. subtilis to prototrophy. The H2 genome is a linear DNA molecule about 129 kb in length. DNA extracted from phage particles grown in B. subtilis is not cut by the restriction endonucleases HaeIII, Fnu4HI, Bsp1286I, and BamHI; the latter enzyme is produced by B. amyloliquefaciens strain H. The prophage in lysogenic B. subtilis cells can be cut by these enzymes. We have isolated H2 mutants that carry the transposon Tn917, or a mutation resulting in clear-plaque morphology, or both.
~~We examined the production of temperate bacteriophages by several strains of Bacillus amyloliquefaciens. Each of the seven strains we induced with mitomycin C produced at least one temperate phage capable of infecting strains of Bacillus subtilis; some of the phages could also infect other B. amyloliquefaciens strains. It is probable that some of the bacteria also produce bacteriocins.
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