Cloning the smell of the seaside - molecular genetics of dimethyl sulphide production by bacteria

我们都去过海滨，我们都被一位知情的父母告知要“呼吸臭氧层”，因为它“对你有好处”。嗯，首先，它不是臭氧，其次，它对你不太好。事实上，这种独特的气味是另一种气体，称为二甲基硫（DMS），自1971年以来，人们就知道它非常重要，每年全世界约有3000万吨二甲基硫被释放到空气中。一旦进入大气层，它就会产生其他主要影响，成为引发海洋上空云层形成的“种子”。事实上，有人提出，这种分子的生产规模如此之大，以至于它对世界气候产生了重大影响。然而，尽管如此，我们完全不知道这个过程是如何在分子水平上发生的。这更加令人惊讶，因为我们已经知道一段时间了，许多海洋细菌（其中一些很容易在实验室中生长）如果提供关键前体分子（简称为二甲基硫基丙酸盐- DMSP），就可以释放DMS。不是每天都能读到的化合物，但在世界的海洋和海岸中有超过20亿吨。这是另一个海滨象征，布莱克浦塔的重量，大约是它的7万倍。棒了这种DMSP分子被大量的海洋植物--海藻和微小的浮游生物--用作缓冲剂，或称为盐保护剂，以抵御海水的盐度。当这些植物死亡时，一些从其中逃逸的DMSP被一些海洋细菌用作食物，当它们这样做时，它们在此过程中将其中一些转化为DMS气体。我们最近从诺福克海岸分离出一种这样的消耗DMSP的细菌，并使用各种分子技术来获得一些相关的基因。通过观察它们的序列，我们可以猜测这些基因可能在做什么，到目前为止，看起来这些机制与以前提出的假设机制非常不同。我们还发现，非常相似的基因存在于其他一些非常意想不到的细菌类型中，例如那些共生地生活在陆地植物根部的细菌。因此，细菌产生二甲硫醚的程度可能比我们想象的要广泛得多。我们现在希望对这个过程有更深入的了解，至少在“我们”的应变。我们想确定和表征所有参与的酶，我们想知道该途径是如何调节的-我们已经知道这些细菌并不愚蠢，因为它们只有在化合物存在于它们的环境中时才会打开降解DMSP的系统。一旦我们知道这种诺福克菌株发生了什么，就可以相当直接地找出其他类型的海洋细菌是否以同样的方式吃DMSP。因此，我们第一次接近于对这一途径的分子细节有一个真实的了解，这样我们就可以在下次去大雅茅斯的时候，当有人问起从金色的沙滩上飘上来的腐烂海藻的微妙气味时，逗我们的朋友们开心，让他们着迷，让他们接受教育。

We've all been to the seaside and we've all been told by a knowing parent to 'breathe in that ozone', because it's 'good for you'. Well, firstly, it's not ozone and second, it's not terribly good for you. That distinctive aroma is, in fact another gas, called dimethyl sulphide (DMS) and it has been known since 1971 that it is hugely important, with some 30 million tons of it being liberated into the air, world wide, every year. And once in the atmosphere it has other major effects, being the 'seed' that sets off cloud formation over the oceans. Indeed, it has been proposed that the production of this molecule is on such a scale that it has major effects on the world's climate. Yet, despite all this, we have absolutely no idea of how, at a molecular level, this process occurs. This is all the more surprising since we have known for some time that many marine bacteria, some of which are easy to grow in the laboratory, can liberate DMS if supplied with the key precursor molecule, called Dimethylsulphiopropionate - DMSP for short. Not a compound one reads about every day, yet there are over two billion tonnes of it in the world's oceans, seas and seashores. That's the weight, give or take, of another seaside symbol, the Blackpool Tower - 70,000 times over. Amazing. This DMSP molecule is used by the great masses of marine plant life - seaweeds and microscopic plankton - as a buffer, or osmo-protectant, against the saltiness of the sea. When these plants die, some of the DMSP that escapes from them is used as food by some marine bacteria and, when they do so, they convert some of it to the DMS gas in the process. We recently isolated one such DMSP-consuming bacterium from the Norfolk coast and used various molecular techniques to get our hands on some of the genes that are involved. By looking at their sequences, we can guess what the genes might be doing and, so far, it looks as if the mechanisms are very different from those hypothetical ones that had been proposed before. We also saw that very similar genes exist in some other, very unexpected, types of bacteria, such as those that live, symbiotically, on the roots of land plants. So the extent of DMS production by bacteria may be far wider and varied than we had thought. We now hope to get a much deeper understanding on this process, at least in 'our' strain. We want to identify and characterize all the enzymes that are involved and we want to know how the pathway is regulated - we already know that these bacteria are not stupid, since they only switch on their systems for degrading the DMSP if the compound is present in their environment. Once we know what is happening with this Norfolk strain, it should be fairly straightforward to find out if other types of marine bacteria that eat DMSP do so in the same way. So, for the first time, we are close to getting a real insight into the molecular details of this pathway, allowing us to amuse, fascinate and educate our friends the next time we go to Great Yarmouth and somebody asks about the delicate scent of rotting seaweed that drifts up from the golden sands.