Bacteria have to deal with viruses in their environment, and we can think about a viral infection like a ticking time bomb -- a bacterium has only a few minutes to defuse the bomb before it gets destroyed. So, many bacteria have in their cells an adaptive immune system called CRISPR, that allows them to detect viral DNA and destroy it.
细菌必须在它们的环境里对付病毒。 我们可以这么想， 病毒感染像是个定时炸弹， 细菌在被消灭前， 只有几分钟时间可以拆除炸弹。 很多细菌在它们的细胞里有一种 适应力免疫系统叫做 "CRISPR" ， 它可以使细菌侦测到 病毒DNA并消灭它。