【分享】Nature: 生命的首个免疫系统

Bacteria Provide Example of One of Nature's First Immune Systems, Research Shows

Nature: 自然界首个免疫系统

译者：Docofsoul


ScienceDaily (Dec. 30, 2010) — Studying how bacteria incorporate foreign DNA from invading viruses into their own regulatory processes, Thomas Wood, professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, is uncovering the secrets of one of nature's most primitive immune systems.

《每日科学》2010年12月30报道 —— 美国德州A&M大学Artie McFerrin化学工程系教授Thomas Wood目前正在研究细菌吸收入侵病毒的异源DNA使之并入其自我调节过程的具体方法，以期揭示自然界最原始的免疫系统之一的内在秘密。


Single gram-negative Escherichia coli bacterium. Studying how bacteria incorporate foreign DNA from invading viruses into their own regulatory processes, Thomas Wood, professor in the Artie McFerrin Department of Chemical Engineering at Texas A&M University, is uncovering the secrets of one of nature's most primitive immune systems. (Credit: Janice Haney Carr)





单个革兰氏阴性大肠杆菌。美国德州A&M大学Artie McFerrin化学工程系教授Thomas Wood目前正在研究细菌吸收入侵病毒的异源DNA使之并入其自我调节过程的具体方法，以期揭示自然界最原始的免疫系统之一的内在秘密。（图片来源： Janice Haney Carr）

His findings, which appear in Nature Communications, a multidisciplinary publication dedicated to research in all areas of the biological, physical and chemical sciences, shed light on how bacteria have throughout the course of millions of years developed resistance to antibiotics by co-opting the DNA of their natural enemies -- viruses.

这一研究发现发表于《Nature Communications》（《自然·通讯》，该刊物发表有关生物、物理、化学等所有领域的研究进展）。论文阐明了细菌通过拉拢其自然界敌人——病毒的DNA，在数百万年中发育出了抗击抗菌素能力的具体过程。

The battle between bacteria and bacteria-eating viruses, Wood explains, has been going on for millions of years, with viruses attempting to replicate themselves by -- in one approach -- invading bacteria cells and integrating themselves into the chromosomes of the bacteria. When this happens a bacterium makes a copy of its chromosome, which includes the virus particle. The virus then can choose at a later time to replicate itself, killing the bacterium -- similar to a ticking time bomb, Wood says.

Wood解释说，细菌与吞噬细菌的病毒之间的战争已经上演了数百万年，因为病毒总在通过（其中一个方法）入侵细菌细胞并与细菌的染色体结合来试图复制其本身。当这种情形发生时，细菌会制作一份包括病毒粒子在内的自身染色体拷贝。在稍后的某个时间，病毒能够决定复制本身，杀死细菌——与定时炸弹引爆情形颇为相似。

However, things can go radically wrong for the virus because of random but abundant mutations that occur within the chromosome of the bacterium. Having already integrated itself into the bacterium's chromosome, the virus is subject to mutation as well, and some of these mutations, Wood explains, render the virus unable to replicate and kill the bacterium.

但是，病毒也会失手，因为细菌染色体内部会出现虽然随机但大量的突变。病毒将自身与细胞的染色体结合后也受到突变的影响。Wood指出，其中一些突变使得病毒无法复制自身并杀死细菌。

With this new diverse blend of genetic material, Wood says, a bacterium not only overcomes the virus' lethal intentions but also flourishes at a greater rate than similar bacteria that have not incorporated viral DNA.

这样，有了这种新的、不同的遗传物质混杂其间，细菌不仅扑灭了病毒的腾腾杀气，而且比起无法与病毒的DNA结合的细菌来，还可以以更高的效率或速率繁殖。

"Over millions of years, this virus becomes a normal part of the bacterium," Wood says. "It brings in new tricks, new genes, new proteins, new enzymes, new things that it can do. The bacterium learns how to do things from this.

Woods进一步解释：“几百万年无声无息地过去了，该病毒顺理成章地登堂入室，成了该细菌的正常组成部分。病毒带来了新的技巧、新的基因、新的蛋白与新的酶，也就是说，带来了病毒能够办到的所有新鲜事物。于是细菌百尺竿头更进一步，学会了在这个基础上进一步发展的方式。”

"What we have found is that with this new viral DNA that has been trapped over millions of years in the chromosome, the cell has created a new immune system," Wood notes. "It has developed new proteins that have enabled it to resists antibiotics and other harmful things that attempt to oxidize cells, such as hydrogen peroxide. These cells that have the new viral set of tricks don't die or don't die as rapidly."

“我们已经发现，自从细菌的染色体内有了这种新的病毒DNA，细胞因而产生一种新的免疫系统，开发出了新的蛋白，能够抵抗抗生素与其它有害的、试图氧化细胞的事物（比如说过氧化氢）。这些具有一整套新病毒技巧的细胞不会死亡或者说不会很快死亡。”

Understanding the significance of viral DNA to bacteria required Wood's research team to delete all of the viral DNA on the chromosome of a bacterium, in this case bacteria from a strain of E. coli. Wood's team, led by postdoctoral researcher Xiaoxue Wang, used what in a sense could be described as "enzymatic scissors" to "cut out" the nine viral patches, which amounted to precisely removing 166,000 nucleotides. Once the viral patches were successfully removed, the team examined how the bacterium cell changed. What they found was a dramatically increased sensitivity to antibiotics by the bacterium.

为了理解病毒DNA对细菌的重要性， Wood的研究小组需要删除细菌染色体内的所有病毒DNA。在本研究中，研究者应用了来自大肠杆菌菌株的细菌。该研究小组由博士后研究员Xiaoxue Wang,率队。实验中用了在某种意义上被形容为“酶剪”的工具来“剪除”九个病毒片段（准确地说这个过程是移除了166,000个核苷酸）。在病毒片段被成功移除后，研究小组检查了细菌细胞的具体变化情况。他们发现：细菌对抗菌素的敏感性激增。

While Wood studied this effect in E. coli bacteria, he says similar processes have taken place on a massive, widespread scale, noting that viral DNA can be found in nearly all bacteria, with some strains possessing as much as 20 percent viral DNA within their chromosome.

当研究大肠杆菌所发生的这种效应时，Wood指出，类似的过程以大规模、广泛传播的方式发生着。他说，几乎所有的细菌内部都找得到病毒DNA的身影，其中一些菌株，其染色体内的病毒DNA占据了20%的比重。

"To put this into perspective, for some bacteria, one-fifth of their chromosome came from their enemy, and until our study, people had largely neglected to study that 20 percent of the chromosome," Wood says. "This viral DNA had been believed to be silent and unimportant, not having much impact on the cell.

Wood说：“总的来看，有些细菌的染色体的五分之一来自其敌人，在我们的研究之前，人们大都忽视对染色体的这20%的研究，认为这种病毒DNA不但已被静默而且也不重要，对细胞的影响无关痛痒。”

"Our study is the first to show that we need to look at all bacteria and look at their old viral particles to see how they are affecting the bacteria's current ability to withstand things like antibiotics. If we can figure out how the cells are more resistant to antibiotics because of this additional DNA, we can perhaps make new, effective antibiotics."

“我们的研究首次显示了：需要关注所有的细菌，关注其古老的病毒粒子，以观察这些病毒粒子影响细菌抵抗诸如抗菌素之类事物能力的具体过程。如果我们彻底了解细胞有了该额外DNA后更有效抵抗抗菌素的具体过程的话，我们就有可能制造新的有效的抗生素。”

看来免疫系统最大的破坏者是微生物