Microbial assimilation of phosphorus in the subtropical Atlantic Ocean: a molecular approach

磷(P)是地球上所有生物的基本元素，无论大小或栖息地如何。微生物是需要磷来合成DNA的积木、构建细胞膜和产生能量转移分子的微生物。在海洋中，磷以三种形式存在：磷酸盐(PO4)、溶解有机磷(DOP)和颗粒态磷(PP)。PO4是海洋微生物最容易用来生长的物质。在沿海或亚极地地区，PO4浓度足够高，足以支持微生物生长。然而，在被称为亚热带环流的海洋区域，表面PO4浓度极低，限制了微生物的生长。相反，DOP的浓度比PO4高100倍。各种各样的微生物生活在这些PO4有限但DOP丰富的区域，但它们如何应对P-压力？微生物是否会争夺相同的小PO4池，或者它们能否进入复杂的DOP池？它们是如何共存的？这里提出的研究将开始回答这些问题。2011年在大西洋的一次研究巡航期间，我们沿着PO4和DOP浓度和有效性的梯度收集了样本。我们建议检查微生物中包含的编码蛋白质的基因的存在和表达，这些蛋白质允许微生物获得P，即P。“p-获得基因”。分子研究表明，一些基因可以产生在极低浓度下结合PO4的蛋白质，或者可以分解结合到有机磷上的P的酶。例如，PhoA基因编码产生碱性磷酸酶，这种酶将磷分解到被称为磷酸单酯的有机分子上，后者占DOP池的20%到75%。因此，拥有PhoA的微生物可以进入DOP池的很大一部分。我们建议确定五个P-获得基因的相对分布。然而，微生物有可能拥有一个基因，但这个基因被关闭了。因此，我们不仅要确定这些基因的存在，还要确定它们是否被激活或被“表达”。我们将针对3个生活在海洋中的生态重要物种：原氯球菌和聚球藻，这是微小的蓝藻，对海洋中的碳循环非常重要，以及毛藻，形成蓝藻的菌落，肉眼可见，在海洋氮循环中发挥重要作用。综上所述，我们建议使用分子技术来确定5个磷获取基因在3个生态重要物种中的存在和表达，沿着磷有效性的梯度。为什么这很重要？副热带涡旋占世界海洋面积的70%。来自大西洋和太平洋的观察表明，由于水柱稳定性和微生物群落结构的变化，这些广阔的区域正在显示出因应气候变化而变暖的迹象。重要的是，据预测，气候变化将加强副热带环流中的磷限制，因此，我们必须了解生态上重要微生物的磷获取基因，以便在不断变化的海洋环境中确定赢家和输家。

Phosphorus (P) is an essential element for all living matter on earth, irrespective of size or habitat. Microbes are microscopic organisms that require P to synthesize building blocks for DNA, build cell envelopes and create energy transfer molecules. In the ocean, P exists in three forms; phosphate (PO4), dissolved organic P (DOP) and particulate P (PP). PO4 is the most readily used by marine microbes for growth. In coastal or subpolar regions, PO4 concentrations are sufficiently high to support microbial growth. However, in regions of the ocean called subtropical gyres, surface PO4 concentrations are extremely low and limit microbial growth. Conversely, DOP concentrations are up to 100 times higher than PO4. A diverse array of microbes live in these PO4-limited but DOP-plentiful regions but how do they cope with P-stress? Do microbes compete for the same small pool of PO4 or can they access the complex DOP pool? How do they co-exist? The research proposed here will begin to answer these questions. During a research cruise in the Atlantic Ocean in 2011, we collected samples along a gradient of PO4 and DOP concentration and availability. We propose to examine the presence and expression of genes contained within microbes that encode for the production of proteins that allow microbes to acquire P, i.e. 'P-acquisition genes'. Molecular studies have shown that some genes can produce proteins that bind PO4 at very low concentrations or enzymes that can cleave P bound to organic phosphorus. For example, the PhoA gene encodes for the production of alkaline phosphatase, an enzyme that cleaves P bound to organic molecules called phosphomonoesters that make up 20 to 75% of the DOP pool. Microbes that possess PhoA can therefore access a large part of the DOP pool. We propose to determine the relative distribution of five P-acquisition genes. However, it is possible for a microbe to possess a gene, but for that gene to be switched off. Therefore, we will not only determine the presence of the genes, but also if they are switched on or are being 'expressed'. We will target 3 ecologically important species living in the ocean: Prochlorococcus and Synechococcus, which are microscopic cyanobacterium that are important for cycling of carbon in the ocean, and Trichodesmium, a colony forming cyanobacteria that are visible to the naked eye and play an important role in the marine nitrogen cycle. In summary, we propose to use molecular techniques to determine the presence and expression of 5 P-acquiring genes in 3 ecologically important species along a gradient in P-availability. Why is this important? Subtropical gyres represent 70% of the world's ocean. Observations from the Atlantic and Pacific Oceans show that these vast regions are showing signs of warming in response to climate change through changes in water column stability and microbial community structure. Importantly, it is predicated that climate change will enhance P-limitation in subtropical gyres and thus it is vital that we understand the P-acquisition genes of ecologically important microbes in order to identify the winners and losers in a changing ocean environment.