A multidisciplinary study of DMSP production and lysis - from enzymes to organisms to process modelling.

海洋浮游植物、海藻、珊瑚、沿海植物以及海洋细菌每年产生10亿吨的相容性溶质二甲基磺基丙酸盐（DMSP）。DMSP在释放到环境中时对海洋生态系统具有关键作用，是海洋微生物群落的生物保护剂和关键营养物。DMSP也是气候冷却气体二甲硫醚（DMS）的主要前体。许多生物裂解二甲基硫醚，每年产生约3亿吨二甲基硫醚，其中约10%被释放到空气中。二甲硫醚在大气中氧化，产生气溶胶，可能导致云量增加，对气候产生潜在影响，或者通过降雨返回陆地，这是全球硫循环的关键一步。DMSP和DMS也是许多生物的化学引诱物，使它们与食物联系在一起。尽管DMSP很重要，但对它如何产生以及为什么产生的知识相当肤浅。我们知道，DMSP和DMS的生产在不同生产者群体之间和内部存在很大差异，但这种差异的原因尚不清楚，主要是因为编码DMSP合成酶的基因尚未被鉴定，而DMSP裂解酶仅在生产DMSP的生物体中被鉴定。我们的初步工作已经鉴定了细菌、硅藻、甲藻、珊瑚和附着植物-海洋DMSP生产者的主要群体。DMSP/DMS生产的差异可能源于它们不同的Dsy酶。我们的目的是确定“为什么某些生物产生的DMSP比其他生物多，以及不同生物对全球DMSP和DMS生产的贡献”。不同生物中DMSP生产的差异可能源于其Dsy酶的不同效率或表达。为了验证这一点，我们将使用生物化学技术来鉴定主要类别的DMSP生产者的不同Dsy酶，我们将研究不同的DMSP生产者如何在不同的条件下表达他们的DMSP和DMS合成酶，因为表达水平可能决定DMSP的产量。这可能有助于了解气候变化的影响，例如，如果Dsy和DMSP裂解酶的表达因温度升高而增加。对于重要的DMSP/DMS生产藻类Emiliania huxleyi和Symbiodinium，我们将精确定位细胞内的Dsy酶，因为这将有助于了解DMSP在这些生物中的作用。通过将细胞位置和Dsy酶学数据与DMSP（和合成中间体）和DMS浓度、关键DMSP生产者的生产速率和增强积累的条件相关联，我们将更充分地理解为什么DMSP和DMS生产存在高度变异性。由于未来环境条件的变化可能会影响到DMSP/DMS的生产，并可能影响到气候，反之亦然，因此必须了解和预测这些影响。由于缺乏结合分子、生物地球化学、工艺和建模数据的综合研究，目前对二甲基甲硫醚/二甲基甲硫醚产量的估计可能不准确。在这里，我们将在英吉利海峡的沿海站点L4进行为期一年的详细研究（选择其位置和上下文数据范围）。我们将研究DMSP/DMS合成中关键基因的多样性和表达，DMSP合成速率，特定组浮游植物DMSP生产，DMSP（和合成中间体）和DMS的大量常备库存以及季节性演替中的微生物多样性。我们的研究将告诉我们哪些生物体产生DMSP/DMS，生产率和浓度，使用的基因以及在什么条件下。利用这些数据，我们将输入临界状态和速率参数到一个新的模型DMSP/DMS动态，使不同类群的DMSP/DMS的全球生产的贡献更准确地预测，沿着任何可能的影响气候变化。

A billion tonnes of the compatible solute dimethylsulfoniopropionate (DMSP) is made each year by marine phytoplankton, seaweeds, corals, coastal plants and, as shown by us, marine bacteria. DMSP has key roles in marine ecosystems when released into the environment, serving as an osmoprotectant and key nutrient for marine microbial communities. DMSP is also the main precursor of the climate-cooling gas dimethylsulfide (DMS). Many organisms cleave DMSP, producing ~300 million tonnes of DMS annually, ~10 % of which is released into the air. DMS oxidises in the atmosphere, producing aerosols that can lead to increased cloud cover and potential effects on climate, or be returned to land in rain, a key step in the global sulfur cycle. DMSP and DMS are also chemoattractants for many organisms which associate them with food.Despite the importance of DMSP, knowledge of how and why it is produced is quite superficial. We know that DMSP and DMS production is highly variable between and within the different groups of producers, but the reasons for this variability are not understood, mainly because genes encoding DMSP synthesis enzymes have yet to be identified and DMSP lyases have only just been identified in a DMSP-producing organism.Our preliminary work has identified dsy genes which encode key DMSP synthesis enzymes in bacteria, diatoms, dinoflagellates, corals and haptophytes - the major groups of marine DMSP-producers. Variability in DMSP/DMS production may stem from their different Dsy enzymes.Our aim is to establish "why some organisms make more DMSP than others and the contribution of different organisms to global DMSP and DMS production".It is possible that variability in DMSP production in different organisms stems from the differing efficiencies or expression of their Dsy enzymes. To test this, we will use biochemical techniques to characterise the different Dsy enzymes of the major classes of DMSP-producers.We will study how diverse, model DMSP-producers express their DMSP and DMS synthesis enzymes in response to varying conditions, since the expression level may govern the amount of DMSP produced. This may shed light on the effects of climate change, e.g., if Dsy and DMSP lyase expression is increased by higher temperatures. For the important DMSP/DMS-producing algae Emiliania huxleyi and Symbiodinium, we will precisely locate the Dsy enzymes within the cell as this will help in understanding the role(s) of DMSP in these organisms. By relating cellular location and Dsy enzymology data to DMSP (and synthesis intermediates) and DMS concentrations, production rates in key DMSP producers and the conditions that enhance accumulation, we will more fully understand why high variability in DMSP and DMS production exists. As future changes in environmental conditions will likely affect DMSP/DMS production, and potentially climate, and vice versa, it is important to understand and predict these effects. Current estimates of DMSP/DMS production are likely inaccurate due to a lack of integrated studies combining molecular, biogeochemical, process and modelling data. Here, we will carry out a detailed, year-long study at the coastal site L4 in the English Channel (chosen for its location and range of contextual data). We will study the diversity and expression of key genes in DMSP/DMS synthesis, DMSP synthesis rates, group-specific phytoplankton DMSP production, bulk standing stocks of DMSP (and synthesis intermediates) and DMS and microbial diversity over a seasonal succession. Our studies will tell us which organisms produce DMSP/DMS, production rates and concentrations, the genes used and under what conditions. Using these data, we will input critical state and rate parameters into a new model for DMSP/DMS dynamics, allowing the contribution of different taxa to global production of DMSP/DMS to be more accurately predicted, along with any possible effects of climate change.