Functional and molecular biodiversity of the bacterial production of the climate-changing gas dimethyl sulphide.

我们都去过海边，一位见多识广的父母告诉我们“呼吸一下臭氧”，因为它“对你有好处”。嗯，首先，它不是臭氧，其次，它对你的身体不是很好。事实上，这种独特的气味是另一种被称为二甲基硫化物(DMS)的气体，自1971年以来，人们一直知道它非常重要，全世界每年约有3000万吨二甲基硫化物释放到空气中。一旦进入大气层，它还会产生其他重大影响，成为在海洋上空形成云层的“种子”。事实上，这种分子的产生规模如此之大，以至于它对世界气候产生了重大影响，这要归功于它对海洋云层的影响。然而，尽管如此，我们直到最近才开始在分子水平上了解这一过程是如何发生的。这更令人惊讶，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生长，如果提供关键的前体分子，简称为二甲基硫代丙酸酯-DMSP，就可以释放出DMS。没有人每天都读到一种化合物，但世界上的海洋和海岸中有超过20亿吨的化合物。这是另一个海滨标志--布莱克浦大厦的重量--7万多倍。太棒了。DMSP被大量的海洋植物--海藻和微小的浮游生物--用作缓冲或渗透保护剂，以抵御海洋的盐度和其他压力。当这些植物死亡时，从它们身上逸出的一些DMSP被一些海洋细菌用作食物，当它们这样做时，它们会在这个过程中将其中的一些转化为DMS气体。我们最近从诺福克海岸分离出了一种这样的消耗DMSP的细菌，称为Marinomonas。我们使用了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，看起来这些机制似乎与之前提出的假设非常不同。我们还发现，在其他一些令人意想不到的细菌中也存在非常相似的基因，比如那些共生在陆地植物根部的细菌。因此，细菌产生DMS的程度可能比我们想象的要广泛和多样得多。同样令人震惊的是，其他已知的从DMSP中产生DMS气体的细菌并不包含我们在我们的马里诺单胞菌菌株中发现的基因。因此，一定有一些根本不同的方式，不同的细菌可以分解DMSP。我们现在计划对已知的DMSP非常丰富的各种环境进行采样，并分离出DMSP降解菌，以寻找这些“新的”DMS排放形式。这些环境的范围从巨蚌的嘴巴，到夏威夷的一些植物的根，再到公海(特别是在它们刚刚经历了巨大的微小浮游生物细胞的激增，在它们临终前释放出大量DMSP的情况下)，以及一些散发DMSP的陆地植物的根表面。我们还将在一些已知产生DMS的细菌物种中寻找基因，但这些细菌物种没有我们在Marinomonas中发现的基因。所有这些都将让我们积累一份关于气候变化过程在不同细菌中发生的不同方式的基因清单。因此，在不远的将来，我们和其他人可以利用这些信息制造分子工具，使我们能够更彻底地调查支撑海边气味的生物多样性。

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, the production of this molecule is on such a scale that it has major effects on the world's climate, thanks to its effect on the cloud cover over the oceans. Yet, despite all this, we have only very recently begun to understand, at a molecular level, how 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 on the lab, 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. The DMSP 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, and against other stresses. 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 that DMS gas in the process. We recently isolated one such DMSP-consuming bacterium, called Marinomonas, from the Norfolk coast. We used various molecular techniques to get our hands on some of the genes that are involved. By looking at their sequences, we could 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. It was also very striking that other bacteria that are known to make the DMS gas from DMSP do not contain the gene that we discovered in 'our' strain of Marinomonas. So, there must be some fundamentally different ways in which different bacteria can break down DMSP. We now plan to sample all sorts of environments that are known to be very rich in DMSP and to isolate DMSP-degrading bacteria in a search for these 'novel' forms of DMS emission. These environments will range from the mouths of giant clams, to the roots of some plants in Hawaii, to the open seas (especially when they have just had a massive 'bloom' of tiny plankton cells that liberate huge amounts of DMSP in their death throes) and also the root surfaces of some of the land plants that exude DMSP. We will also look for the genes in some of the bacterial species that are already known to be DMS producers, but which do not have the genes that we had identified in Marinomonas. All this will let us amass a genetic inventory of the different ways in which this climate-changing process occurs in different bacteria. So, in the not-too-distant future, we, and others, can use this information to make molecular tools that will allow us to investigate, even more thoroughly, the biodiversity that underpins the smell of the seaside.