Can Microplastic Pollution Change Important Aquatic Bacterial Communities?

摘要（ABSTRECT）

“科学家已经发现，微塑料正在污染世界各地的环境，这包括我们的海洋以及沿海地带。其中一些塑料会进入一个尤为重要的环境——海岸沉积物中或水下的泥土层。这种沉积物是多种多样的细菌的生活家园，这些细菌在生态系统的营养物循环中发挥着重要的作用。这些细菌对营造健康的环境至关重要，但也很容易受到环境污染的影响。不幸的是，人们对这些细菌是如何对微塑料污染做出反应的仍知之甚少。我们研究了不同微塑料对生活在海底沉积物中的细菌的影响，也研究了之后其对营养物循环的影响。我们首次发现，不同的微塑料可以显著地改变这些细菌群落和碳循环，我们应该对其做进一步的研究，以了解其对我们自然环境带来的持久影响。

Scientists have discovered that microplastics are polluting many environments worldwide, including our oceans and coastlines. Some of these plastics will make their way into a particularly important environment—coastal sediments, or the layer of mud below the water. This sediment is home to diverse bacterial life, which plays a key role in nutrient cycles of the ecosystem. These bacteria are critical for healthy environments, but are also easily affected by environmental pollution. Unfortunately, little is known about how the bacteria respond to microplastic pollution. We studied the effects of different microplastics on bacteria living in marine sediments, as well as the subsequent impacts on nutrient cycling. We found, for the first time, that different microplastics can significantly alter these bacterial communities and the nitrogen cycle, which should be studied further to understand lasting impacts on our natural environments.”

微塑料污染

MICROPLASTIC POLLUTION

你可能已经听说过微塑料，但你可能并不清楚它们是什么，也不知道为什么大家似乎都在谈论它们。微塑料十分简单——它们是一些小型塑料，一般是5mm宽（大约是橡皮的大小）甚至更小。塑料可以被制造成微塑料般的大小，如添加到护肤品或牙膏中的小塑料珠。然而，在大多数情况下，微塑料来自于较大塑料块的分解。在海洋环境中尤为如此，大量的塑料垃圾随着时间的推移不断积累，它们暴露在大风、海浪和阳光下，最终形成微塑料。

You may have heard of microplastics, but you may not know what they are or why everyone seems to be talking about them. Microplastics are simple—they are small bits of plastic, generally 5 mm wide (about the size of a pencil eraser) or smaller. Plastics can be manufactured to be microplastic size, such as small beads that are added to skin care products or toothpaste. Most often, however, microplastics come from the breakdown of larger pieces of plastic. This is especially true in the ocean environment, where a lot of plastic trash accumulates over time and is exposed to wind, waves, and sunlight, eventually creating microplastics [1]!

尽管这听起来十分简单，但环境中的微塑料是十分复杂的。这是因为存在着不同类型的塑料。任何塑料的构件和构成的“脊梁”都被称为聚合物。常见的塑料最常以其聚合物命名，如聚乙烯和聚氯乙烯。此外，还会经常添加其他化学物品以帮助塑料产品达到所用目的。这些所谓的添加剂各种各样，也可包括颜色燃料。因此，没有两块塑料是完全相同的。

While this sounds simple, microplastics in the environment are extremely complex. This is because there are many different kinds of plastics. The building blocks or “backbone” of any plastic are called polymers. Common plastics are most often named after their polymer, for example, polyethylene or polyvinyl chloride. In addition, other chemicals are often added to help a plastic product serve its purpose. These so-called additives vary, but can include color dyes, for example. As such, no two microplastics are identical to each other [2].

近些年来，科学家发现微塑料污染已十分普遍，而且是由于人口增长以及塑料用量的增加而不断增加的。在海洋、湖泊、河流和土壤中，在遥远的山顶上，在冰川的冰层里，都能找到微塑料，有些微塑料还悬浮在大气中！在水生环境里，微生物在沉积物中积聚——沉淀在水底的泥土层中。许多不同的动物生活在沉积物中，它们可能会与微塑料污染相互作用。科学家一直在竭力了解形形色色的微塑料可能对生物的影响。

In recent years, scientists have discovered that microplastic pollution is widespread, and is growing due to population rise and increasing plastic usage. Microplastics have been found in oceans, lakes, rivers, and soils, on remote mountain tops, inside glacier ice, and suspended in the air [1]! In aquatic environments, microplastics accumulate in sediment—the layers of mud and dirt that settle to the bottom, below the water. Many different animals live in the sediment and may interact with the microplastic pollution. Scientists have been working to understand the effects that diverse microplastics might have on living things [1].

沉积物细菌群落

THE SEDIMENT BACTERIAL COMMUNITY

如果你对溪流、湖泊以及河流里对沉积物进行探察，你会发现许多活生生的生物，举几个例子而言，就如蠕虫、蛤蜊和螃蟹。但如果你用显微镜对沉积物进行探察，你会发现还有丰富的微生物群落（即肉眼看不到的生物）。细菌是一种微生物，在沉积物中尤为丰富。成千上万的细菌共存，形成了一个细菌群落，科学家们通过物种的种类以及每个物种存在的数量来描述沉积物的细菌群落。这些细菌群落对整个生态系统起着非常重要的作用。

If you explore sediments in streams, lakes, and rivers, you will discover many living organisms—worms, clams, and crabs, to name a few. But if you explore sediment with a microscope, you will see that there is also a rich community of microbes (i.e., organisms that cannot be seen with the naked eye)! Bacteria are a type of microbe that are very abundant in sediments. Thousands of species of bacteria co-exist, forming a bacterial community. Scientists describe bacterial sediment communities by the kinds of species and how many of each species are present. These bacterial communities perform very important jobs for the entire ecosystem.

沉积物细菌群落的另一个作用就是转化营养物质。植物和动物（包括人类）需要营养素来构建必要的生物大分子，这些大分子包括蛋白质和DNA。在你肠道里的细菌的帮助下，你可以从食物中摄取营养物质。当你在吃东西时，消化道里的细菌会帮助身体消化食物，从而释放出你身体所需的营养素。沉积物细菌对水中的生物也起着同样的作用。当有机质（如死去的生物和粪便）沉入沉积物时，大多数营养物质仍然会被困在里面，无法供其他生物体利用。沉积物里的细菌就会分解这些有机质，从而为它们自身以及其他生物释放出营养素（图1）。与此同时，它们还会确保任何一种营养素都不会过多，因为过多可能会对它们造成伤害。因此，细菌群落会影响那些可以生活在该环境的高等生物的类型与健康。

One of the roles of sediment bacterial communities is transforming nutrients. Nutrients are needed by plants and animals (including humans) to build essential biomolecules, including proteins and DNA. You get nutrients from food, with the help of bacteria inside your gut. When you eat food, bacteria in your digestive tract help process the food to release the nutrients that your body needs. Sediment bacteria do the same thing for organisms in the water. When organic material, such as dead organisms or feces, sink to the sediments, most nutrients are still trapped inside and not available for other living organisms to use. The bacteria in sediments break down organic material, releasing nutrients for themselves and for other organisms (Figure 1). At the same time, they also make sure there is not too much of any one nutrient, which may cause harm. Thus, the bacterial community affects the types and health of higher organisms that can live in that environment.

图1-沉积物中的细菌和你肠道中的细菌起着相类似的作用---帮助处理营养物质！左图说明了这在水生环境中的作用，有机物（通常是死去的生物体和排遗废物，但最近也有塑料）被沉积物中的细菌处理。

右图将其比作你的肠道，肠道里的细菌帮助处理你每天摄入的有机物（即食物）！（用BioRender.com创建）。

Figure 1 - The bacteria in sediments and those in your gut serve similar roles—helping to process nutrients! The left side of the figure illustrates how this works in the aquatic environment, where organic matter (generally dead organisms and wastes, but more recently, plastic) is processed by bacteria in the sediments.

The right side compares this to your gut, where bacteria help process the organic matter (i.e., food) that you eat every day! (Created with BioRender.com).

沉积物中的氮循环

THE SEDIMENT NITROGEN CYCLE

沉积物细菌帮助调控的一个重要营养素是氮。氮循环十分复杂，因此我们只需关注它的一些重要特征。在沉积物和水中，许多不同的物质都含有氮元素，这包括铵盐（NH4+）和硝酸盐（NO3−）。不同的细菌可以将这些化合物从一种形式转化到另一种形式。沉积物中的两个非常重要的转化是硝化作用和反硝化作用。这两个过程可以结合在一起，即通过硝化作用可将铵盐转化为硝酸盐，通过反硝化作用可将硝酸盐转化为氮气（N2）（图2）。

An important nutrient that sediment bacteria help regulate is nitrogen. The nitrogen cycle is complex, so we will only focus on a few of its features. In sediments and water, many different chemicals contain nitrogen, including ammonium (NH4+) and nitrate (NO3−). Different bacteria can transform these compounds from one form to another. Two very important transformations in sediments are nitrification and denitrification. Both processes can work in combination to convert ammonium to nitrate via nitrification, and nitrate to dinitrogen gas (N2) via denitrification (Figure 2A).

图2-（A）水生沉积物中氮循环的关键组成部分

（B）我们在实验中看到的硝化作用（蓝色）和反硝化作用（红色）的变化，显示了在容器中将每种类型的塑料添加到沉积物的微生态系统上面。聚乳酸和聚氨酯泡沫微塑料都增强了硝化作用和反硝化作用；聚氯乙烯减轻了这两个过程；与没有添加微塑料的对照组相比，聚乙烯没有明显改变任何过程（用BioRender.com创建）。

Figure 2 - (A) Key components of the nitrogen cycle in aquatic sediments.

(B) The changes to nitrification (blue) and denitrification (red) that we saw in our experiment are shown above the microcosms containing each type of plastic added to sediments. Both polylactic acid and polyurethane foam microplastics increased nitrification and denitrification; polyvinyl chloride decreased both processes; polyethylene did not significantly change either process compared to the control with no added microplastics (Created with BioRender.com).

拥有适量的合适细菌可以确保生态系统中存在着适量的铵盐和硝酸盐。如果这个平衡发生错乱，生态系统就会发生改变或受到伤害。特别的，应该要有足够的细菌来完成硝化作用和反硝化作用，从而除去多余的铵盐（这些多余的铵盐对环境有害），但又不能完全去除铵盐（适量的铵盐是供其他生物体生命活动的重要营养物质）。所有对氮循环的不同步骤起着重要作用的细菌物种都有着不一样的遗传密码。科学家可以解读这些密码来了解存在的细菌物种有哪些，以及它们在营养物循环中起着怎样的作用。我们决定利用这个手段提出两个问题。

Having the right bacteria in the right amounts ensures that the correct level of ammonium and nitrate are present in an ecosystem. If the balance is wrong, the ecosystem can be changed or harmed. Specifically, there should be sufficient bacteria that complete nitrification and denitrification to remove excess ammonium (which can harm the environment), but not too much to completely remove ammonium (which, in the right amount, is an important nutrient for other organisms). All bacterial species that are important for different steps of nitrogen cycling have a different genetic code. Scientists can read this code to see which bacterial species are present and what roles in the nutrient cycle they perform. We decided to use this tool to ask two important questions.

我们的实验

OUR EXPERIMENT

我们提出的两个问题是：沉积物中不同的微塑料是否会改变细菌群落的组成成分？如果是这样的话，这是否会影响氮元素转化的进程？为了回答这些问题，我们设立了一个实验！我们从当地的一个沼泽中收集了一些沉积物，并把这些沉积物分散装在多个容器中，然后加水，从而创造出一个生态系统的小型复制品，我们把这称为“微观生态环境”，我们往不同容器里的沉积物中添加了四种不同类型的微塑料，分别是聚乙烯、聚氯乙烯、聚氨酯泡沫和聚乳酸。这些微塑料是通过在一个专门的研磨机中研磨较大的塑料块制成的。因此它们含有不同的聚合物和添加剂，对细菌群落产生的影响也各不相同。我们也弄了一个没有添加任何微塑料的容器，以代表正常情况。我们把这称为对照。我们对这些容器进行了超过16天的观察。

Our two questions were: Do different microplastics in sediments change the bacterial community composition? And if so, does this also affect nitrogen-transforming activities? To answer these, we set up an experiment! We collected sediment from a local marsh, distributed it into containers, and added water to create smaller replicas of the natural ecosystem, called microcosms. We added four different types of microplastics to the sediments in the different containers: polyethylene, polyvinyl chloride, polyurethane foam, and polylactic acid. These microplastics were made by grinding larger pieces of plastic in a specialized grinder. These microplastics are used for different purposes, so they contain different polymers and additives that could affect the bacterial community differently. We also made one container with no added microplastics, to represent a normal situation. This is called a control. The containers were monitored over 16 days.

通过解读每个微观生态环境中存在的细菌的遗传密码，我们分析了实验前、实验中和实验后的沉积物中的细菌群落。首先，我们利用这些信息来描述细菌群落的特征——存在的物种有哪些？它们的丰裕度如何？紧接着，我们专门寻找了负责硝化作用和反硝化作用的遗传密码。我们对比了不同微生态环境中所看到的结果，以了解微塑料是否改变了细菌群落的氮循环。

We analyzed the bacterial communities in the sediments before, during, and after the experiment by reading the genetic codes of the bacteria present in each microcosm. First, we used this information to characterize the bacterial community—what species are present and how abundant are they? Then, we specifically looked for the parts of the genetic code responsible for nitrification and denitrification. We compared our findings between the different microcosms, to see if the microplastics changed the bacterial community or nitrogen cycling.

我们发现添加了微塑料的容器中的细菌群落确实与对照组存在差异，且聚合物的类型导致了它们的千变万化！我们也发现微塑料会影响氮循环，即它们改变了能够进行硝化和反硝化作用的细菌的物种丰度。我们发现，经过聚氯乙烯处理的沉积物在实验结束时细菌群落的变化最大，在含有聚氯乙烯微塑料的沉积物中，细菌的硝化作用和反硝化作用明显受到抑制。然而在含有聚乳酸和聚氨酯泡沫微塑料的微生态环境中，硝化作用和反硝化作用得到了提升。含有聚乙烯的微生态环境与我们的对照组结果相近，这揭示了这种塑料没有像其他塑料那样对沉积物细菌群落影响那么大（图2B）。这个实验告诉我们环境中的微生物污染可能会影响关键的细菌群落和氮循环。

We discovered that the communities containing added microplastics were indeed different from the control, and the polymer types resulted in different changes! We also found that the microplastics affected nitrogen cycling activities; i.e., they altered the abundance of species capable of performing nitrification and denitrification. We found that polyvinyl chloride-treated sediments had the biggest change in the bacterial community at the end of the experiment. In sediments with polyvinyl chloride microplastics, nitrification and denitrification were significantly reduced. In the microcosms with polylactic acid and polyurethane foam microplastics, however, nitrification and denitrification were elevated. The microcosms with polyethylene microplastics were similar to our control, suggesting this plastic did not affect the sediment bacterial community as much as the other plastics (Figure 2B). This experiment told us that microplastic pollution in the environment may affect key bacterial communities and the nitrogen cycle.

为何如此重要？

WHY DOES THIS MATTER?

科学家们早已知道，在细菌的驱动下，沉积物在营养物循环中发挥着重要作用。营养物循环对生活在沉积物里的生物至关重要，且对覆盖在上层水和其他地方的生物也是如此。科学家们最近了解到，大量的微塑料正在污染全球的水生沉积物，而我们的研究正是第一个关于微塑料可以影响沉积物细菌群落，从而影响其氮循环活动的报告。沉积物中氮循环的平衡使营养物质保持在合适的水平，以保证现存动物的健康，这些动物包括蠕虫、鱼类、浮游植物和水生草类！有了这些知识，我们可以跟进研究上的一些重要问题。哪些类型的塑料所造成的有害影响最大？这些危害是由聚合物还是由添加剂造成的？这些沉积物中必须含有多少塑料才能影响细菌群落？当我们有了这些知识，科学家可以与决策者合作，帮助保护沿海地区免受微塑料污染的有害影响。

Scientists have long known that sediments play an important role in nutrient cycles, driven by the bacteria. Nutrient cycles are critical to organisms living in the sediments, but also those in the overlying water and beyond. Scientists have recently learned that large amounts of microplastics are polluting aquatic sediments globally, and our research is the first report that microplastics can affect the sediment bacterial community, and therefore affect their nitrogen-cycling activities. The balance of the nitrogen cycle in sediments keeps the nutrients at the right levels for the health of the animals present, including worms, fish, phytoplankton, and aquatic grasses! With this knowledge, we can follow up with important research questions: Which types of plastic cause the most harmful effects? Is that harm caused by the polymer or the additives? And how much plastic must be in those sediments to affect the bacterial community? When we have this knowledge, scientists can work with policy makers to help protect coastal zones from the harmful effects of microplastic pollution.

大多数的微塑料是由较大的塑料块在环境中分解后形成的。因此，如果我们想阻止微塑料污染，我们必须杜绝塑料污染！尽管塑料污染并不仅仅发生在我们乱扔垃圾的时候。有时人类产生了大量的塑料垃圾，在到达垃圾填埋场之前，它们就已经逃到了环境中。这可能是由于垃圾桶溢出，垃圾袋从卡车上飘出，或垃圾被风暴卷走，到达当地的河流、湖泊或海洋。如果我们减少塑料垃圾，就会有更少的垃圾泄露在环境中。你可能会想到一些可以减少你每天产生塑料垃圾的方法，或者可以寻找到泄漏到环境中的塑料碎片的地方。这两点都是减少微塑料污染的关键步骤!

Most microplastics are formed when bigger pieces of plastic break down in the environment. So, if we want to stop microplastic pollution, we must stop plastic pollution! Plastic pollution does not only happen when we litter, though. Humans produce a lot of plastic trash and, sometimes, it escapes into the environment before it reaches the landfill. This can happen because of an overflowing trash can, a trash bag being lost off a truck, or trash that is swept away in a storm and reaches a local river, lake, or ocean. If we reduce our plastic waste, there will be less that can leak into the environment. You may think of some ways that you can reduce the plastic trash you generate every day, or places where plastic debris leaking into the environment could be captured. Both are critical steps toward reducing microplastic pollution!

Glossary 术语表

Microplastic: ↑ A plastic particle that is <5 mm in the longest direction, often formed by the breakdown of larger pieces of plastic in the environment.

微塑料：小于5毫米的塑料颗粒，通常由环境中较大的塑料碎片分解形成

Polymer: ↑ Large chemicals that form the building blocks of plastics, often called the plastic “backbone.”

聚合物：构成塑料构件的大分子化学物质，通常称为塑料的"骨架"。

Sediment: ↑ The layers of mud and sand that settle below the water.

沉积物：沉淀在水底的泥土层和沙层

Bacterial Community: ↑ A group of different species of bacteria that live in the same environment.

微生物群落：一组生活在同一环境中的不同种类的细菌。

Nitrogen: ↑ An essential element that is used to build many of the compounds that living things need to survive.

氮：一种不可或缺的元素，用于构建生物体生存所需的许多化合物。

Nitrification: ↑ A process that converts one form of nitrogen, ammonium (NH4+), to another form, nitrate (NO3−), which is made possible by microbes.

硝化作用：将一种形式的氮，即铵盐（NH4+）转化为另一种形式的硝酸盐（NO3-）的过程，这是通过微生物完成的。

Denitrification: ↑ A process that converts one form of nitrogen, nitrate (NO3−), to another form, nitrogen gas (N2), which is made possible by microbes.

反硝化作用： 将一种形式的氮，即硝酸盐（NO3-），转化为氮气（N2）的过程，这是通过微生物完成的。

Microcosm: ↑ A small replica of a natural environment, used by scientists to answer research questions about how different things may change that environment.

微生态环境：一个自然生态环境的小型复制品，科学家用它来解答关于不同事物如何改变该环境的研究性问题。

附上作者信息

翻译者小婧唠叨几句：

太久没更新啦，最近发生太多事情，也比较忙吧...之后还有不到一个月的时间期末考试，期末考试后就步入高三了，至于翻译吧，我还是会尽我所能更新的！

个人认为这篇文章真的很不错，在给我们介绍了微生物污染的同时还通过设计实验让我们明白了不同塑料对沉积物细菌群落的影响。其实设计实验真的很重要，现在考试也是经常考的，是考察一个人实验能力的体现，而多看这方面的文章可以不断培养这方面的能力，这是一个不断积累的过程。

也没那么多时间细细审稿了，文章有笔误之处或翻译的有瑕疵之处还望海涵！