Kasman Laura M., Porter La Donna
Medical University of South Carolina
Dignity Health - St. Joseph's MC
Bacteriophages, also known as phages, are viruses that infect and replicate only in bacterial cells. They are ubiquitous in the environment and recognized as the earth's most abundant biological agent. They are extremely diverse in size, morphology, and genomic organization. However, all consist of a nucleic acid genome encased in a shell of phage-encoded capsid proteins, which protect the genetic material and mediate its delivery into the next host cell. Electron microscopy has allowed the detailed visualization of hundreds of phage types, some of which appear to have "heads," "legs," and "tails." Despite this appearance, phages are non-motile and depend upon Brownian motion to reach their targets. Like all viruses, bacteriophages are very species-specific about their hosts and usually only infect a single bacterial species or even specific strains within a species. Once a bacteriophage attaches to a susceptible host, it pursues 1 of 2 replication strategies: lytic or lysogenic. During a lytic replication cycle, a phage attaches to a susceptible host bacterium, introduces its genome into the host cell cytoplasm, and utilizes the host's ribosomes to manufacture its proteins. The host cell resources are rapidly converted to viral genomes and capsid proteins, which assemble into multiple copies of the original phage. As the host cell dies, it is either actively or passively lysed, releasing the new bacteriophage to infect another host cell. In the lysogenic replication cycle, the phage also attaches to a susceptible host bacterium and introduces its genome into the host cell cytoplasm. However, the phage genome is instead integrated into the bacterial cell chromosome or maintained as an episomal element where, in both cases, it is replicated and passed on to daughter bacterial cells without killing them. Integrated phage genomes are termed prophages; the bacteria containing them are termed lysogens. Prophages can convert to a lytic replication cycle and kill their host, most often in response to changing environmental conditions.
噬菌体，也被称为 phages，是一类仅在细菌细胞中感染和复制的病毒。它们在环境中无处不在，被认为是地球上最为丰富的生物因子。它们在大小、形态和基因组组织方面极其多样。然而，所有噬菌体均由包裹在噬菌体编码的衣壳蛋白外壳中的核酸基因组组成，这些蛋白保护遗传物质并介导其传递到下一个宿主细胞中。电子显微镜已使数百种噬菌体类型得以详细可视化，其中一些看起来有“头部”“腿部”和“尾部”。尽管有这种外观，但噬菌体是无运动能力的，依靠布朗运动来抵达它们的目标。与所有病毒一样，噬菌体对其宿主具有很强的物种特异性，通常仅感染单一细菌物种甚至一个物种内的特定菌株。一旦噬菌体附着到易感宿主上，它会采取两种复制策略之一：裂解性或溶原性。在裂解性复制周期中，噬菌体附着到易感宿主细菌上，将其基因组引入宿主细胞质中，并利用宿主的核糖体制造其蛋白质。宿主细胞资源迅速转化为病毒基因组和衣壳蛋白，这些组装成原始噬菌体的多个副本。随着宿主细胞死亡，它要么被主动要么被被动裂解，释放出新的噬菌体去感染另一个宿主细胞。在溶原性复制周期中，噬菌体同样附着到易感宿主细菌上并将其基因组引入宿主细胞质中。然而，噬菌体基因组反而整合到细菌染色体中或作为附加体元件维持，在这两种情况下，它都会被复制并传递给子代细菌细胞而不杀死它们。整合的噬菌体基因组被称为原噬菌体；含有它们的细菌被称为溶原菌。原噬菌体可以转变为裂解性复制周期并杀死其宿主，最常见的是对不断变化的环境条件做出反应。
