Biochemical and genetic diversity of a critical step in the sulphur cycle - molecular studies of bacterial dimethyl sulphide production

气体二甲基硫（简称DMS）对动物有奇怪的作用。像小虾一样的甲壳类动物，一些海鸟甚至是海豹都会对它感到兴奋，因为它的香味是附近食物的标志。而且，对于普通民众来说，这是一个非常喜爱的纪念品的日子由海滩，是一部分令人回味的气味的海边。但DMS远比这重要得多。它是硫从海洋转移到陆地的主要途径，因此是自然硫循环的关键部分，生物体将硫从一种形式转移到另一种形式。你可能不知道，但你体内的许多分子都含有硫，没有它我们就无法生存。二甲硫醚对我们的环境也很重要，因为当它进入空气中时，它被氧化形成其他化合物，这些化合物充当海洋上空云层形成的“种子”，就像灰尘的波动引发水晶花园中的结晶一样。这可能会影响我们的气候，通过减少到达地球表面的光量，甚至可能导致“全球变暗”。此外，它的氧化对酸雨现象有很大的贡献。二甲基硫醚在海洋中大量产生--每年约3亿吨。它是由微生物产生的，微生物使用另一种分子，有一个可笑的长名字-二甲基磺基丙酸酯（DMSP）-作为食物来源。这种DMSP是由海藻和海洋中大量的浮游生物制造的，帮助它们在海洋生活的压力下生存下来。当它们死亡时，DMSP被释放出来，然后被一些细菌和真菌吃掉，其中一些产生DMS作为副产品。其他细菌则更有教养--它们以一种非常不同的方式吞噬DMSP，这种方式不会产生这种微生物含硫的打嗝。考虑到DMS的重要性，今天我们对它产生的遗传基础知之甚少是相当令人惊讶的。然而，东安格利亚大学的科学家们最近取得了一项重要突破，确定了参与制造DMS的细菌基因。在这样做的过程中，他们发现了至少三种完全不同的细菌制造这种气体的方式。不仅如此，在自然环境中，这些基因可以在非常不同的海洋细菌之间转移。更值得注意的是，它们从一些细菌转移到完全不同的生命形式，如真菌。而且，这些酶中的一些，以及含有它们的生物体，是从未被怀疑参与这一重要过程的类型。格鲁吉亚大学的其他研究人员已经对那些对不产生DMS的途径很重要的基因做了相关的研究。利用这些信息和他们自己的发现，UEA研究小组发现了一种海洋细菌--叫做Roseovarius nubinhibens --它是一种真实的DMSP暴食者。它有两种，可能是三种不同的方式来制造DMS，如果这还不够的话，它还可以通过另一种不制造DMS的途径来分解DMSP。UEA小组现在想看看在这个物种中制造DMS的酶的特性，并看看单个细菌如何在不同的情况下决定它应该使用哪种不同的途径-可用的DMSP浓度，培养基的酸度，细胞密度等等。通过了解这些新发现的系统的这些特征，我们将更好地了解细菌如何以及为什么选择以一种方式而不是另一种方式分解DMSP，以及为什么有些细菌产生大量重要的气体，而另一些细菌只产生一点。这些知识将为地球上生命最重要的元素之一的自然循环提供新的见解。

The gas dimethyl sulphide (DMS for short) does strange things to animals. Tiny shrimp-like crustaceans, some seabirds and even harbour seals get excited by it, since its aroma is a sign of nearby food. And, for the general populace, it is a much-loved memento of days by the beach, being part of the evocative smell of the seaside. But DMS is much more important than that. It represents the major route for transfer of sulphur from the oceans to land and, as such, is a critical part of the natural sulphur cycle, in which living organisms transfer sulphur from one form to another. You may not know it, but many of the molecules in your body contain sulphur and without it we cannot survive. DMS is also important for our environment because when it gets into the air, it is oxidised to form other compounds that act as 'seeds' for cloud formation over the oceans, just as flecks of dust set off crystallisation in crystal gardens. This may affect our climate, by reducing the amounts of light that reaches Earth's surface, perhaps even causing 'global diming'. Furthermore, its oxidation contributes significantly to the phenomenon of acid rain. DMS is made in huge amounts in the oceans - around 300 million tons each year. It is generated by microbes that use another molecule, with a ridiculously long name - dimethylsulphoniopropionate, (DMSP) - as a food source. This DMSP is made by seaweeds and the masses of plankton in the oceans, helping them to survive the stresses of life at sea. When they die, the DMSP is liberated, and is then eaten by some bacteria and fungi, and some of these produce the DMS as a by-product. Other bacteria are more genteel - they devour DMSP in a very different way, which does not produce this microbial sulphurous burp. Given the importance of DMS, it is quite astonishing that today we know so little about genetic basis of its prodution. However, scientists at the University of East Anglia have recently made an important breakthrough by identifying the bacterial genes that are involved in making the DMS. In doing this, they have uncovered at least three completely different ways in which bacteria can make this gas. Not only that, but in the natural environment, these genes can be transferred among very different marine bacteria. Even more remarkably, they were transferred from some bacteria to completely different life forms, such as fungi. And, some of these enzymes, and the organisms that contain them, are of types that had never been suspected of being involved in this important process. Other researchers, at the University of Georgia, have done related work on the genes that are important for the pathway that does not make DMS. Using that information, and their own findings, the UEA group have found one marine bacterium - called Roseovarius nubinhibens - which is a real glutton for DMSP. It has two, possibly three, different ways to make DMS and, as if that were not enough, it can also break down DMSP by the other pathway that does not make DMS. The UEA group now wants to look at the properties of the enzymes that make DMS in this species and to see how a single bacterium decides which of its different pathways it should use under different circumstances - the concentration of the DMSP that is available, the acidity of the medium, the cell density and so on. By learning about these features on these newly discovered systems, we will be much better placed to understand how and why bacteria choose to break down the DMSP in one way, rather than another, and why some make lots of the important gas, but others only make a little. This knowledge will provide great new insights into the natural cycling of one of the most important elements for life on earth.