Abedon Stephen T, Hyman Paul, Thomas Cameron
Department of Microbiology, Ohio State University, Mansfield, Ohio, USA.
Appl Environ Microbiol. 2003 Dec;69(12):7499-506. doi: 10.1128/AEM.69.12.7499-7506.2003.
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.
对于专性裂解噬菌体而言，在繁殖力（爆发量）和潜伏期（世代时间的一个组成部分）之间存在着一种权衡。这种权衡的出现是因为从受感染细菌中释放噬菌体后代与产生更多噬菌体后代所需机制的破坏同时发生。在此，我们利用噬菌体突变体来探讨噬菌体潜伏期进化与噬菌体敏感细菌密度之间的关系。理论表明，更高的细菌密度应选择更短的噬菌体潜伏期。我们一致发现，更高的宿主密度（>/==约10^7个细菌/毫升）能够富集噬菌体RB69的菌株，这些变体的潜伏期比野生型短。其中一个这样的变体，称为sta5，其潜伏期约为野生型的70%至80%——几乎与RB69的隐蔽期一样短——并且其相应的爆发量约为野生型的30%。我们表明，在更高的宿主密度（>/==约10^7个细菌/毫升）下，sta5噬菌体能够胜过RB69野生型，不过仅在直接（同培养物）竞争的条件下。我们将这种优势解释为对应于sta5种群增长略快，导致在同培养物生长期间突变频率增加数倍。然而，当野生型和突变体之间存在间接（不同培养物）竞争时，或者当存在同培养物竞争但噬菌体敏感细菌密度较低（</=约10^6个细菌/毫升）时，sta5的优势就会丧失。基于这些观察结果，我们认为，当培养物中的细菌高度普遍且培养物之间的传播容易实现时，表现出非常短潜伏期的噬菌体可被视为繁殖的专家。
