How do eukaryotic phytoplankton produce the most abundant organo-sulphur compound in the world's oceans?

有一种分子，叫做二甲基磺基丙酸酯（DMSP），它是由无数微小的单细胞海洋浮游生物，许多海藻和一些生活在海边的陆地植物大量制造的-每年十亿吨。在其中一些中，大部分硫和大部分碳以这种分子的形式存在，但DMSP的影响甚至比这更广泛。尽管DMSP含量丰富，但对于DMSP的功能还没有明确的共识--也许它可以缓冲海水的盐度，也许它可以作为防御捕食者攻击的防御化合物，也许它可以抵御紫外线。- 也许它是一个分子杰克的所有行业。DMSP不仅是有趣的本身，但它也有一个化学遗产，因为它是母体化合物的其他分子也非常重要。当制造DMSP的植物样生物体将其释放到环境中时，无论是通过泄漏，还是当它们被病毒或微观动物裂解时，它都被大量的海洋细菌和一些真菌用作DMSP催化过程中的美味食物来源。这代表了全球硫循环的很大一部分，但这还不是全部。DMSP的分解产物之一是一种称为二甲基硫的气体，其本身具有重要的环境影响。每年在海洋及其边缘产生的3亿吨二甲硫醚中，约有10%逃逸到大气中，在那里被氧化成硫酸盐和硫酸。这些分子作为“云凝结核”，导致云的形成，就像灰尘的斑点可以开始晶体生长在水晶花园。这种情况发生的规模如此之大，以至于它是海洋上空大部分云层的原因，并可能影响到达地球的太阳热和光的数量-一种“全球变暗”的形式。二甲硫醚也是许多海洋动物-鸟类、海豹和小型甲壳类动物-的信号，因为它是浮游生物食物供应的化学标志。对于我们这些智人来说，DMS是海边气味的一部分，特别是当有很多海藻的时候。虽然已经有一些很好的初步研究，描述了DMSP合成的一般途径，但在任何产生DMSP的生物体中都没有发现纯化的酶或相应的基因。这种知识的缺乏使得人们很难清楚地了解DMSP的真正功能。这项研究的重点是一组浮游植物，统称为硅藻，它们产生大量的DMSP。这些微小的类似植物的生物在世界海洋中大量存在--总的来说，它们占地球植物重量的四分之一，它们产生的氧气与我们呼吸的氧气比例大致相同。我们最近在硅藻中发现了四个关键基因，我们坚信这些基因编码参与DMSP生产的酶。我们现在计划研究这些基因和它们编码的酶的确切功能，方法是制造不再制造DMSP的突变体，反过来，通过工程改造菌株来过量生产DMSP。这将使我们能够在任何生物体中第一次确定这个关键分子的功能。我们还将发现这些基因是如何表达的;它们是一直处于开启状态，还是对（例如）环境中的各种压力做出反应？不同物种之间是否存在差异？这不仅将为DMSP在硅藻中的作用提供新的见解，而且我们的研究结果还将揭示在其他重要的海洋生物中参与这一过程的机制。这些研究只会加强我们评估未来环境变化对这一关键生物合成过程的影响的能力。

There is a molecule, called dimethylsulphoniopropionate (DMSP) which is made in very large amounts - a billion tons per year, worldwide - by myriads of tiny single-celled marine plankton, many seaweeds and a few land plants that live near the seaside. In some of these, most of the sulphur and much of the carbon is in the form of this molecule, but the influence of DMSP is even more wide-ranging than that. Despite its abundance, there is no clear agreement as to what is the function of the DMSP - maybe it buffers the cells from the saltiness of the sea, maybe it acts as a defence compound against attack by predators, maybe it protects against ultraviolet light. - maybe it is a molecular jack of all trades.DMSP is not only interesting in its own right, but it also has a chemical legacy, since it is the parent compound for other molecules that are also very important. When the plant-like organisms that make DMSP release it into the environment, either by leakage, or more dramatically when they are lysed by viruses or microscopic animals, it is used as a tasty food source by the teeming marine bacteria and some fungi in a process of DMSP catabolism. This represents a massive part of the global sulphur cycle, but even that is not all. One of the DMSP breakdown products is a gas, called dimethyl sulphide (DMS), which has important environmental impacts in its own right. Of the 300 million tons of DMS made each year in the oceans and their margins, around 10% escapes into the atmosphere, where it gets oxidised to sulphate and sulphuric acid. These molecules act as "Cloud Condensation Nuclei", which cause clouds to form, just as specks of dust can start crystals growing in crystal gardens. This occurs on such a scale that it is responsible for much of the cloud cover over the seas and oceans and may affect the amount of solar heat and light that arrives on Earth - a form of "Global Dimming". The DMS also acts as a signal for many marine animals - birds, seals and tiny crustaceans - since it is a chemical signature for their plankton food supplies. Also to us, as Homo sapiens, DMS is part of the smell of the seaside, especially when there is a lot of seaweed about.Although there have been some nice preliminary studies in which the general pathways for DMSP synthesis have been described, none of the purified enzymes or corresponding genes have been identified in any DMSP-producing organism. This lack of knowledge has made it hard to work out unambiguously what are the true functions of DMSP.This study focuses on one group of phytoplankton, collectively known as diatoms, which produce large amounts of DMSP. These microscopic plant-like organisms are abundant in the world's oceans - all told, they make up a quarter of Earth's plant life by weight and they produce around the same proportion of the oxygen that we breathe. We have very recently identified four key genes in diatoms that we strongly believe encode enzymes that are involved in DMSP production. We now plan to study the exact functions of these genes and the enzymes that they encode by making mutants that no longer make DMSP and, conversely, by engineering strains that over-produce it. This will allow us, for the first time in any organism, to figure out with certainty what are the functions of this key molecule. We will also discover how the genes are expressed; are they switched on all the time, or do they respond to (for example) various stresses in the environment? Does this differ between different species? Not only will this provide new insights on the role(s) of DMSP in diatoms, but our results should shed light on the mechanisms that are involved in this process in other important marine organisms that make this key molecule. Such studies will only strengthen our ability to assess the effects of future environmental changes on this crucial biosynthetic process.