追捕病原菌的生物工程菌

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追捕病原菌的生物工程菌
大肠杆菌寻找并摧毁入侵病菌而不伤害有益细菌。
在抗感染的斗争中，药品需要一个英雄。生物工程菌横空出世，它能追踪并捕获最终通过一两次强大攻击破坏病原体。
来自新加坡南洋理工大学的生物合成学家 Matthew Chang已经改造了带有“探寻和追杀”系统的针对绿脓杆菌的生物工程大肠杆菌。绿脓杆菌是一种侵入性细菌，能引起肺炎和其他疾病。在感染小鼠的初步测试中，注入改造生物工程大肠杆菌，在其身后留下一串死绿脓杆菌。
Chang和他的团队最早开发了一种大肠杆菌，它能分泌一种抗菌蛋白--pyocin，每当它检测到猎物释放的化学信号，然后它就释放这种致命物质。

研究者在大肠杆菌内转入基因，产生一种杀伤蛋白，叫做microcin S (MccS). 它比pyocin蛋白小，因此大肠杆菌能分泌这种蛋白，而不是运送蛋白到自杀爆发点。这就意味着，较少的改造工程菌就能抗感染。

研发团队在工程菌内转入基因产生核酸酶，称为DNase I。这是一个高效的酶，能通过降解帮助绿脓杆菌被膜聚集在一起的核苷酸，而穿过绿脓杆菌的被膜。
研发团队编码了大肠杆菌，因此它能“狡猾”地保持干燥，直到接近目标。它能发现绿脓杆菌控制群体感应进程的信使分子。通过群体感应，入侵者能够评估它的群体密度。每一个大肠杆菌产生一个蛋白，该蛋白能够缠绕群体感应分子，形成复合物，它能激活武器攻击系统。
复合物控制大肠杆菌的运动，所以大肠杆菌移动到高群体感应分子浓度的地方，该过程叫做趋化。由于来到猎物旁边，大肠杆菌产生了更多的杀伤产物。
“这才是整个工作的精华，”来自马里兰大学公园学院的生物合成专家 William Bentley说，“这是真正的创新。这些其中的策略已经在其他生物工程细菌上单独使用，但是把它们结合在一起是全新的。”成果在本周的ACS Synthetic Biology上发表。

有工程菌，无感染
Chang将工程菌喂给感染绿脓杆菌的小鼠，几小时后收集粪便样本。他发现给予工程菌的小鼠和给予普通大肠杆菌的相比，前者粪便中病原体较少，看起来没有受疾病影响。“这是相当理想的效果，”Chang说。
但是这样的工程菌能够使用在人类身上吗？“我认为可以，”Chang回答说。举例来说，最常规的抗生素治疗，在肠道中不分青红皂白地杀死细菌，包括病原微生物和有益的细菌。与此相反，Chang的改造大肠杆菌能提供外科手术式的打击。
Chang还建议病菌可能给人类带来高的致病风险。大肠杆菌在小肠内潜伏，只有它的敌人出现，它才能被激活。“当然，也存在监管障碍：这些是转基因生物，”Chang说。“但是最终，如果我们能证明这些大肠杆菌是安全和有效的话，我真的可以想象它可以用于人类。”
Bentley和他的团队使用了相似的方法改造工程菌，使之能发现癌细胞然后到达位置是释放致死化合物。他现在和Chang一起完成一个US Defense Threat Reduction Agency资助的项目，改造新的大肠杆菌能够消除绿脓杆菌以外的病原体。

其他研究者也使用相似的系统。例如，在剑桥的麻省理工的Ron Weiss和他的团队最近制作了大肠杆菌能发现绿脓杆菌的相同的信使分子，响应时释放抗菌化合物。
Chang也正在视图改善他的工程菌定位系统，提供其穿透成熟生物膜能力。他正在给他的菌株抓住目标微生物的能力，使它们逃脱不了。从现在起，病原体不得不问它们一个问题：我感到幸运吗?绿脓杆菌你呢？

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Engineered bacterium hunts down pathogens

E. coli microbe seeks out and destroys invaders without harming helpful bacteria.

In the war against infection, medicine needs a hero. Meet the bioengineered bacterium that can hunt down pathogens and destroy them with a powerful one–two punch.

Synthetic biologist Matthew Chang at Nanyang Technological University in Singapore has armed Escherichia coli bacteria with a ‘seek and kill’ system that targets cells of Pseudomonas aeruginosa, an invasive bacterium that causes pneumonia and other illnesses1. In preliminary tests with infected mice, the modified bacterium left a trail of dead P. aeruginosa in its wake.

Chang and his team had previously developed an E. coli that could brew up an antibacterial peptide called pyocin, and then explode to release its deadly cargo whenever it detected a chemical signal emitted by its prey2. Now the bioengineered vigilante is back — and it is tougher than ever.
The researchers inserted genes into E. coli to make a killing peptide called microcin S (MccS). This is smaller than pyocin, so the E. coli can secrete it, rather than delivering the payload in a single suicidal burst. That means that fewer of the modified bacteria are required to treat an infection.

The team then loaded the engineered bacterium with genes to make a nuclease called DNase I. This efficiently slices through the protective biofilm that envelops P. aeruginosa colonies by breaking down the nucleic acids that help to hold the biofilm together.

The researchers programmed their E. coli so that it cunningly keeps its powder dry until it is close to its mark. It can detect a P. aeruginosa messenger molecule used for a process called quorum sensing, by which the invader assesses its own population density. Each E. coli generates a protein that latches on to a quorum-sensing molecule, forming a complex that activates its weapons systems.

That complex also controls E. coli’s movement, so that the bacterium swims towards higher concentrations of a quorum-sensing molecule — a process called chemotaxis. As it homes in on its quarry, the E. coli ramps up its ammunition production.

“That’s the real gem of this work,” says William Bentley, a synthetic biologist at the University of Maryland in College Park. “I think it’s really innovative.” Some of these tactics have been used individually in other bioengineered bacteria, but “putting it all together is totally new”, says Bentley. The assassin is unveiled this week in ACS Synthetic Biology1.

E. coli 1, infection 0

Chang fed his microscopic mercenaries to mice infected with P. aeruginosa, then collected faecal samples a few hours later. He found that the animals had fewer pathogens than those given ordinary E. coli. and appeared to suffer no ill effects from the treatment. “It’s quite promising,” says Chang.

But can such engineered bacteria ever be used in humans? “I believe so,” says Chang. Most conventional antibiotic treatments kill bacteria indiscriminately, taking out both pathogenic microbes and beneficial bacteria in the gut, for example. By contrast, Chang’s E. coli offers the possibility of a surgical strike.

Chang also suggests that the bacterium could be given to people at high risk of pathogenic infection. The E. coli would lie dormant in the gut, and activate only once its enemy makes an appearance. “Of course there are regulatory hurdles: these are genetically modified organisms,” says Chang. “But eventually, if we can demonstrate that it is safe and effective, I really envision that this could be used in humans.”

Bentley and his collaborators have used a similar approach to make bacteria that seek out cancer cells, and deliver a burst of chemicals when they arrive2. He is now working with Chang on a project funded by the US Defense Threat Reduction Agency to produce a version of E. coli that can neutralize pathogens other than P. aeruginosa. “We wanted to get his ability to target bacteria,” says Bentley.

Other researchers have been working on similar systems. For example, Ron Weiss and colleagues at the Massachusetts Institute of Technology in Cambridge, recently made an E. coli that could detect the same messenger molecule from P. aeruginosa, and deliver an antimicrobial compound in response3.

Chang is also trying to improve his bacterium’s targeting system and boost its ability to cut through mature biofilms. He is giving his E. coli the ability to grab onto enemy microbes so that they cannot escape. From now on, pathogens may have to ask themselves one question: Do I feel lucky? Well, do you, P. aeruginosa?