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，以及如我们所示的海洋细菌，每年产生十亿吨的相容性溶质二甲基磺酰丙酸（DMSP）。DMSP释放到环境中，在海洋生态系统中起着关键作用，是海洋微生物群落的渗透保护剂和关键营养物质。DMSP也是气候冷却气体二甲基硫化物（DMS）的主要前体。许多生物分解DMSP，每年产生约3亿吨DMS，其中约10%被释放到空气中。DMS在大气中氧化，产生的气溶胶会导致云量增加和对气候的潜在影响，或者以降雨的形式返回陆地，这是全球硫循环的关键步骤。DMSP和DMS也是许多与食物有关的生物的化学引诱剂。尽管DMSP很重要，但关于它是如何产生以及为什么产生的知识却相当肤浅。我们知道DMSP和DMS的生产在不同的生产者群体之间和内部是高度可变的，但这种可变性的原因尚不清楚，主要是因为编码DMSP合成酶的基因尚未被确定，DMSP裂解酶仅在DMSP生产生物中被确定。我们的初步工作已经确定了编码DMSP关键合成酶的dsy基因，这些基因存在于细菌、硅藻、鞭毛藻、珊瑚和haptophytes -海洋DMSP产生的主要群体中。DMSP/DMS生产的差异可能源于它们不同的Dsy酶。我们的目标是确定“为什么有些生物比其他生物产生更多的DMSP，以及不同生物对全球DMSP和DMS生产的贡献”。不同生物DMSP产生的差异可能源于其Dsy酶的不同效率或表达。为了验证这一点，我们将使用生化技术来表征dmsp生产者的主要类别的不同Dsy酶。我们将研究模型DMSP生产者如何在不同条件下表达他们的DMSP和DMS合成酶，因为表达水平可能决定DMSP的产量。这可能会揭示气候变化的影响，例如，Dsy和DMSP裂解酶的表达是否会因温度升高而增加。对于产生DMSP/ dms的重要藻类赫胥利Emiliania huxleyi和共生藻，我们将精确定位细胞内的Dsy酶，这将有助于理解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生产者的生产速率以及促进积累的条件联系起来，我们将更充分地了解DMSP和DMS生产存在高可变性的原因。由于未来环境条件的变化可能会影响DMSP/DMS的生产，并可能影响气候，反之亦然，因此了解和预测这些影响非常重要。由于缺乏结合分子、生物地球化学、过程和建模数据的综合研究，目前对DMSP/DMS产量的估计可能不准确。在这里，我们将在英吉利海峡的海岸站点L4（选择它的位置和上下文数据范围）进行为期一年的详细研究。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，群体特异性浮游植物DMSP产量，DMSP（和合成中间体）的大量常备储量以及DMS和微生物多样性在季节演替中的变化。我们的研究将告诉我们哪些生物产生DMSP/DMS，生产速率和浓度，使用的基因以及在什么条件下。利用这些数据，我们将把临界状态和速率参数输入到DMSP/DMS动态的新模型中，从而可以更准确地预测不同分类群对DMSP/DMS全球产量的贡献，以及气候变化的任何可能影响。

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.