Abedon Stephen T
Department of Microbiology; The Ohio State University; Mansfield, OH USA.
Bacteriophage. 2011 May;1(3):179-181. doi: 10.4161/bact.1.3.16709. Epub 2011 May 1.
CRISPR systems, as bacterial defenses against phages, logically must display in their functioning a sequence of at least three major steps. These, in order of occurrence, are "facilitation," adaptation and interference, where the facilitation step is the main issue considered in this commentary. Interference is the blocking of phage infections as mediated in part by CRISPR spacer sequences. Adaptation, at least as narrowly defined, is the acquisition of these spacer sequences by CRISPR loci. Facilitation, in turn and as defined here, corresponds to phage-naïve bacteria avoiding death follow first-time exposure to specific phages, where bacterial survival of course is necessary for subsequent spacer acquisition. Working from a variety of perspectives, I argue that a requirement for facilitation suggests that CRISPR systems may play secondary rather than primary roles as bacterial defenses, particularly against more virulent phages. So considered, the role of facilitation in CRISPR functioning could be viewed as analogous to the building, in vertebrate animals, of adaptive immunity upon an immunological foundation comprised of mechanisms that are both more generally acting and innate.
CRISPR系统作为细菌抵御噬菌体的防御机制，从逻辑上讲，其功能必然展现出至少三个主要步骤。按发生顺序，这些步骤依次为“促进”、适应和干扰，其中促进步骤是本评论所考虑的主要问题。干扰是指部分由CRISPR间隔序列介导的对噬菌体感染的阻断。适应，至少就狭义而言，是指CRISPR基因座获取这些间隔序列。反过来，这里所定义的促进对应于初次接触特定噬菌体后未接触过噬菌体的细菌避免死亡，当然细菌存活对于随后获取间隔序列是必要的。从多个角度出发，我认为促进的必要性表明CRISPR系统作为细菌防御机制可能发挥的是次要而非主要作用，尤其是针对毒性更强的噬菌体。如此看来，促进在CRISPR功能中的作用可被视为类似于在脊椎动物中，基于更普遍起作用且与生俱来的机制所构成的免疫基础构建适应性免疫。
