Bacteria make DMSP - how significant is this process?

全球每年生产10亿吨含硫分子二甲基磺基丙酸酯(DMSP)。人们普遍认为DMSP只由海洋真核生物产生，包括浮游植物、海藻、少数植物和一些珊瑚，但我们的初步工作表明，海洋细菌也能产生DMSP，其水平与一些浮游植物的水平相似。我们第一次证明了海洋细菌可能使用DMSP作为渗透保护剂来缓冲细胞免受海水盐度的影响。我们提出的研究将重新定义DMSP生产及其分解代谢的领域。DMSP是环境友好的气体二甲基硫化物(DMS)的主要前体。微生物裂解DMSP每年产生约3亿吨DMS。这种DMS的大部分被细菌利用，但大约10%从海洋释放到空气中，给海边带来了特有的气味。一旦进入大气层，DMS氧化产生的化学产物有助于海洋上空云层的形成，从而影响到达地球表面的阳光，从而影响气候。反过来，这些产品以雨水的形式返回地球，代表着全球硫循环的关键组成部分。DMS对包括海鸟、甲壳动物和海洋哺乳动物在内的许多生物也是一种强有力的趋化剂，这些生物将DMS与食物联系在一起。尽管以前的研究描述了DMSP的合成途径，但在任何产生DMSP的生物中都没有发现任何酶或相应的基因。我们的初步数据：1.表明一些海洋细菌通过与浮游植物相同的途径合成DMSP。确定了细菌DMSP合成的关键基因“MmtB”--第一个在任何生物体中参与DMSP合成的基因。表明我们的模型海洋细菌Labrenzia很可能将DMSP作为渗透保护剂。表明含有MmtB的细菌产生DMSP，一些细菌还含有DMSP裂解酶基因，其产物从DMSP中释放出DMS。我们的项目：MmtB基因编码一种酶，催化DMSP合成中四个预测步骤中的一个，但我们不知道其他三个基因的同一性。为了充分了解细菌中DMSP的合成过程，我们需要确定缺失的合成基因，以便研究它们的调节和酶学。我们将使用互补的分子遗传学方法来识别未知的DMSP合成基因，并在此过程中表征其表达受到拉布伦齐盐度影响的全部基因。为了了解环境中的细菌如何以及为什么产生DMSP和DMS，我们将研究从海洋样本中分离的关键模式细菌。这些细菌将在与其自然栖息地相似的条件下在微型宇宙中生长，它们的环境生长条件将有所不同，同时在过程和基因表达水平上监测DMS和DMSP的合成。这将表明环境因素，如温度，氧化应激等，是否影响DMSP的产生，以及伴随而来的气候活性气体DMS的产生。我们将对选定的海洋环境进行采样，并与真核细胞的DMS/DMSP途径进行比较，研究细菌DMSP合成的活性。我们将确定在我们的模式细菌中调节DMS/DMSP生产的环境因素是否对重要海洋环境中存在的自然微生物群落具有相同的影响。我们还将使用一套强大的微生物生态学技术，结合分子遗传工具，识别在这些环境中通过MmtB酶产生DMSP的微生物和关键基因。这项工作将帮助我们在未来模拟环境变化如何影响这些气候过程的平衡。

Globally, a billion tons of the sulfur-containing molecule dimethylsulfoniopropionate (DMSP) is made each year. The common belief was that DMSP is only made by marine eukaryotes, including phytoplankton, seaweeds, a few plants and some corals, but our preliminary work shows that marine bacteria also make DMSP, and at levels similar to those reported for some phytoplankton. For the first time, we have shown that marine bacteria likely use DMSP as an osmoprotectant to buffer cells against the salinity of seawater. The research that we propose will redefine the field of DMSP production and its catabolism.DMSP is the main precursor of the environmentally important gas dimethylsulfide (DMS). Microbial DMSP lysis generates ~300 million tons of DMS per annum. Much of this DMS is used by bacteria, but ~10 % is released from the seas into the air, giving the seaside its characteristic smell. Once in the atmosphere, chemical products arising from DMS oxidation aid cloud formation over the oceans, to an extent that affects sunlight reaching the Earth's surface, with effects on climate. In turn, these products are delivered back to Earth as rain, representing a key component of the global sulfur cycle. DMS is also a potent chemoattractant for many organisms including seabirds, crustaceans and marine mammals, which associate DMS with food.Although previous studies have described the pathways for DMSP synthesis, remarkably NONE of the enzymes or corresponding genes have been identified in ANY DMSP-producing organism.Our preliminary data:1. show that some marine bacteria make DMSP via the same pathway used by phytoplankton.2. identified the key gene in bacterial DMSP production "mmtB" - the first gene shown to be involved in DMSP synthesis in any organism.3. show that our model marine bacterium Labrenzia likely makes DMSP as an osmoprotectant.4. show that bacteria containing mmtB produce DMSP, and some also contain DMSP lyase genes whose products liberate DMS from DMSP.5. show that the mmtB gene is abundant in marine environments.Our project:The mmtB gene encodes an enzyme that catalyses one of the four predicted steps in DMSP synthesis, but we do not know the identity the other three genes. To fully understand the process of DMSP synthesis in bacteria, we need to identify the missing synthesis genes so that we can study their regulation and enzymology. We will use complementary molecular genetic approaches to identify the unknown DMSP synthesis genes and, in the process, characterise the full complement of genes whose expression is affected by salinity in Labrenzia.To understand how and why bacteria in the environment produce DMSP and DMS, we will study key model bacteria isolated from marine samples. These bacteria will be grown in microcosms under conditions similar to those of their natural habitat, and their environmental growth conditions will be varied whilst monitoring DMS and DMSP synthesis, at both the process and gene expression level. This will indicate whether environmental factors such as temperature, oxidative stress, etc., affect the production of DMSP and concomitantly the production of the climate-active gas DMS.The importance of bacterial DMSP production in marine environments will be examined. We will sample selected marine environments and investigate the activity of bacterial DMSP synthesis compared to eukaryotic DMS/DMSP pathways. We will determine if the environmental factors that regulate DMS/DMSP production in our model bacteria have the same effect on natural microbial communities that are present in important marine environments. We will also use a powerful suite of microbial ecology techniques, combined with molecular genetic tools, to identify the microbes and key genes involved in producing DMSP via the MmtB enzyme in these environments. This work will help us in the future to model how changes in the environment impact on the balance of these climate processes.