科学美国人Scientific American EP381 |益生菌可以帮助拯救过热的珊瑚

Sarah Vitak: This is Scientific American’s 60-Second Science. I’m Sarah Vitak. 


Charles Darwin’s famous trip on the HMS Beagle is primarily known for bringing us the concept of evolution. But  Darwin also investigated coral reefs and their formation. One thing about reefs in particular really confused him—that conundrum became known as Darwin’s reef paradox. The paradox is this:


Voolstra: How can you find this lush, teeming of life in the otherwise, nutrient depleted ocean.


Vitak: That’s Dr. Christian Voolstra, a professor at the University of Konstanz in Germany. 


Voolstra: And the trick is symbiosis. Corals are basically sessile organisms or animals, so they basically pick a place and they sit and then they cannot move. So the way they make a living is that they team up with micro algae inside the tissues. And this is essentially tiny plants that do photosynthesis. And this photosynthesis generates sugars. And these sugars will be essentially delivered to the coral animals. 


Vitak: These little critters across the globe are in great peril a lot of danger. According to a report from the Global Coral Reef Monitoring Network published in October 2021, we lost 14% of the world’s coral reefs in the last decade. This was mostly due to large scale bleaching events. Coral bleaching is triggered by changes in the coral's environment—including increased temperature, sunlight, or pollutants. But what exactly does it mean for coral to be bleached?


Voolstra: The color of corals comes from the photosynthetic pigments of the algae. So the minute these algae are out, the coral looks white. So what happens in bleaching is that these symbiotic algae or tiny plant cells are getting expelled out of the coral tissue.


If the environmental conditions actually become better again, they can actually take up their algae again and they are fine. So this is a transitory state. But In actuality, if the environmental conditions persist, the coral literally starves to death.


Vitak: Dr. Voolstra and his team were really interested in research that took a new approach to helping coral cope with increased ocean temperatures: treating them with probiotics. [Christian R. Voolstra et al., Extending the natural adaptive capacity of coral holobionts]


Voolstra: The general consumer knows that you can buy yogurt with probiotic cultures, right? There are some bacteria that are good for your gut.


Vitak: Just like humans, coral have a microbiome; a community of microorganisms that live on or inside them. Previous work had shown that bolstering the coral’s bacterial microbiome by giving them doses of probiotics helped them survive challenging conditions. The process is similar to how we work with microbiomes and probiotics in people.


Voolstra: You extract microbes from these very resilient individuals, and then you literally transplant them or offer them to less resilient individuals of the same coral species. So it's not that you're putting something there that wasn't there, but it's really like this human fecal transplants. You have a healthy donor, and you offer these bacteria to an affected recipient.


Vitak: This had already been shown as a proof of concept in previous research. But Dr. Voolstra and his team wanted to drill down and understand it a bit better. 


To do the experiment, they worked in what they call “mesochosms”—sort of a sweet spot between a sterile isolated lab setting and a totally wild reef setting. Basically, they had aquariums with multiple types of corals and some other critters. This allowed them to control conditions but also get a slightly more real-world result. 


One very convenient thing about working with coral is that they are colonial organisms.


Voolstra: Which means that they consist of repetition of the same building blocks. From one colony, you can generate many, many fragments or pieces that all have the exact same genotype with this exact same environmental history. And then you can put them into different conditions. 


Vitak: Once they had their fragments they treated some of them with a mixture of bacteria that they had carefully isolated, selected, and grown from resilient coral—and, of course, they wanted to have a control for their experiment as well,  so they gave some a placebo saline solution.


Finally, they slowly cranked up the heat to simulate ocean warming. 


Voolstra: And this was a very long experiment that essentially lasted over 75 days. 


Vitak: What they found was fascinating. All the coral showed signs of bleaching as the temperature increased, but the coral treated with probiotics recovered faster. And they were 40% more likely to survive.


Voolstra: Okay, like as a coral biologist, or as a biologist, in general, I think you're usually very happy if you have a 5% effect or something observable that you can count with reasonable numbers. This is massive. I mean, if you almost double the survivorship, this is huge.


Vitak: The team also looked at how  adding this probiotic cocktail changed the coral’s microbiome and—how it changed the coral itself. Adding the probiotic changed the composition of the coral’s microbiome. 


Voolstra: It also instigated a change in the expression of certain genes in the coral host. And those genes, were really kind of the go-to genes that you would bet on if this is for increased recovery. 


Vitak: So basically—things like repair genes, immunity genes, and stress response genes. 


Voolstra:  So this is kind of the cliffhanger of this study, you actually change stuff in the host. And in the correlate host, and we don't know how long these changes will stay on. Of course, if those changes can be kept long term, you would not need to keep this probiotic treatment going on and on, right? 


Vitak: Which would be amazing in terms of translating this to the real world. 


Voolstra: I mean, there’s 300,000 square kilometers of coral reef. There's billions of coral. So if you want to bring a little magic potion underwater and inoculate each coral, this becomes unmanageable. No organism makes a living in isolation. And I think we're just getting better at understanding this.


Vitak: Thanks for listening. For Scientific American’s 60 Second Science, I’m Sarah Vitak. 

【参考译文】

Sarah Vitak：这里是《科学美国人》的60秒科学节目。我是莎拉-维塔克。


查尔斯-达尔文在贝格尔号上的著名旅行主要是因为给我们带来了进化的概念而闻名。但是达尔文也调查了珊瑚礁及其形成。特别是关于珊瑚礁的一件事让他非常困惑--这个难题被称为达尔文的珊瑚礁悖论。这个悖论是这样的。


伍尔斯特拉：你怎么能在营养匮乏的海洋中找到如此茂盛的生命。


维塔克：这就是德国康斯坦茨大学的教授克里斯蒂安-武尔斯特拉博士。


伍尔斯特拉。诀窍是共生。珊瑚基本上是无柄生物或动物，所以它们基本上选择一个地方，然后坐着，然后它们不能移动。因此，它们谋生的方式是，它们与组织内的微型藻类合作。而这基本上是进行光合作用的微小植物。而这种光合作用会产生糖。而这些糖分基本上会被输送到珊瑚动物身上。


维塔克：全球各地的这些小动物正处于巨大的危险之中，有很多危险。根据全球珊瑚礁监测网络2021年10月发表的一份报告，在过去十年中，我们失去了世界上14%的珊瑚礁。这主要是由于大规模的白化事件。珊瑚白化是由珊瑚环境的变化引发的--包括温度升高、阳光或污染物。但是，珊瑚白化究竟意味着什么？


伍尔斯特拉。珊瑚的颜色来自于藻类的光合作用色素。所以这些藻类一出来，珊瑚就看起来是白色的。所以在白化中发生的情况是，这些共生藻类或微小的植物细胞被驱逐出珊瑚组织。


如果环境条件实际上再次变得更好，它们实际上可以再次吸收它们的藻类，它们就会好起来。所以这是一个过渡性的状态。但实际上，如果环境条件持续下去，珊瑚实际上是饿死的。


Vitak：Voolstra博士和他的团队对采取新方法帮助珊瑚应对海洋温度上升的研究非常感兴趣：用益生菌治疗它们。[Christian R. Voolstra等人，扩展珊瑚整体生物的自然适应能力] 。


Voolstra。普通消费者知道你可以买到含有益生菌培养物的酸奶，对吗？有一些细菌对你的肠道有好处。


维塔克：就像人类一样，珊瑚有一个微生物组；一个生活在它们身上或体内的微生物群落。以前的工作表明，通过给珊瑚提供一定剂量的益生菌来增强它们的细菌微生物群，有助于它们在充满挑战的条件下生存。这个过程类似于我们在人身上使用微生物组和益生菌的过程。


Voolstra: 你从这些非常有弹性的个体中提取微生物，然后你把它们移植或提供给同一珊瑚物种中弹性较差的个体。因此，这并不是说你在那里放了什么东西，但它真的就像这种人类的粪便移植。你有一个健康的捐赠者，你把这些细菌提供给一个受影响的接受者。


维塔克：这在以前的研究中已经被证明是一个概念。但是Voolstra博士和他的团队想深入研究并更好地理解它。


为了做这个实验，他们在所谓的 "中间体 "中工作--一种介于无菌隔离的实验室环境和完全野生的珊瑚礁环境之间的甜蜜点。基本上，他们的水族箱里有多种类型的珊瑚和其他一些小动物。这使他们能够控制条件，但也得到一个稍微真实的结果。


与珊瑚打交道的一个非常方便的事情是，它们是殖民有机体。


Voolstra。这意味着它们由相同的构件的重复组成。从一个殖民地，你可以产生许多，许多片段或碎片，它们都具有完全相同的基因型和完全相同的环境历史。然后你可以把它们放到不同的条件下。


维塔克：一旦他们得到了他们的碎片，他们就用他们精心分离、选择和从有弹性的珊瑚中培养出来的细菌混合物来处理其中的一些碎片，当然，他们也想为他们的实验做一个对照，所以他们给了一些安慰剂盐水。


最后，他们慢慢调高了温度，以模拟海洋变暖。


Voolstra。这是一个非常漫长的实验，基本上持续了75天。


维塔克：他们的发现很吸引人。随着温度的升高，所有的珊瑚都出现了白化的迹象，但是用益生菌处理的珊瑚恢复得更快。而且它们存活的可能性增加了40%。


伍尔斯特拉。好吧，作为一个珊瑚生物学家，或者作为一个生物学家，一般来说，我认为如果你有5%的效果或者你可以用合理的数字计算的可观察的东西，你通常会非常高兴。这是巨大的。我的意思是，如果你的存活率几乎翻倍，这就是巨大的。


维塔克：研究小组还研究了如何添加这种益生菌cocktai

Vitak：研究小组还研究了加入这种益生菌鸡尾酒如何改变珊瑚的微生物组，以及如何改变珊瑚本身。添加益生菌改变了珊瑚微生物组的组成。


Voolstra：它还促使珊瑚宿主中某些基因的表达发生变化。而这些基因，确实是一种你会赌上的首选基因，如果这是为了增加恢复。


维塔克：所以基本上，像修复基因、免疫基因和压力反应基因。


伍尔斯特拉。 所以这是这项研究的一个悬念，你实际上改变了宿主的东西。而在相关的宿主中，我们不知道这些变化会保持多久。当然，如果这些变化可以长期保持，你就不需要不断地保持这种益生菌治疗，对吗？


维塔克：就将此转化为现实世界而言，这将是非常了不起的。


Voolstra：我是说，有30万平方公里的珊瑚礁。有数十亿的珊瑚。因此，如果你想在水下带一个小魔药，给每个珊瑚接种，这就变得无法管理了。没有任何生物能在孤立的情况下谋生。我认为我们对这个问题的理解越来越深刻了。


维塔克：谢谢你的聆听。在《科学美国人》的60秒科学节目中，我是Sarah Vitak。