Exploring the Linkages Between Trichodesmium spp. Physiology, Diversity and Iron Geochemistry in the Ocean

ABSTRACTProposal没有。当前位置长期以来被认为是海洋中占主导地位的重氮营养型蓝藻（Trichodesmium spp.）的固氮速率可能受到铁和/或磷的限制。虽然模式已经确定了海洋内重氮营养体，特别是trichodesium，预计将受到铁、光、磷或不受这些因素限制的区域，但这些区域的边界是不确定的。模型的实证验证需要实地调查，如果没有对铁或磷限制的快速诊断，很难进行实地调查。南加州大学的两名研究人员发现了几种铁和磷限制的诊断基因，这些基因有助于快速评估天然木霉种群在空间和时间上的铁和磷状态。这些基因也可以提供对铁摄取机制的见解。例如，铁胁迫诱导的基因之一是feoB，预计它是有效吸收铁（II）所必需的。虽然在兼性厌氧细菌中很常见，但它在开放海洋蓝藻中的存在仅限于Trichodesmium和另一种重氮营养菌鳄鱼。pi假设，由于重氮营养体对氮的固定比其他蓝藻有更高的铁需求，它们可能利用feoB，可能与外源性或内源性还原酶机制一起，在海水中溶解的铁池中获取额外的铁库。pi将研究西太平洋暖池中铁和磷诊断探针的表达，以确定该地区的Trichodesmium是否受铁或磷限制。在2007年从新西兰到夏威夷的一次已经获得资助的航行中，他们预计会在南北和东西向的横断面上遇到明显的铁梯度，这些横断面跨越了铁含量限制的范围。将进行铁和铁形态的测量，包括应用新方法将铁形态的当前检测极限扩展到亚纳摩尔水平。通过跟踪夏威夷海洋时间序列站（HOT）在夏末出现的特征性Trichodesmium丰度最大值，还将研究铁形态参数与铁应力诊断之间关系的时间方面。该建议的更广泛影响的一个组成部分是验证当前的全球海洋模型预测。该项目还将在一个重要但尚未得到充分研究的海洋环境中建立一个大型铁浓度测量数据集。此外，该项目将资助两名研究生的研究，并包括来自小型四年制大学的本科生在游轮上的参与。

ABSTRACTProposal No.: OCE-0623499Rates of nitrogen fixation by the colonial cyanobacteria, Trichodesmium spp., long considered the dominant diazotroph in the ocean, can be limited by iron and/or phosphorus. Although models have defined regions within the oceans where diazotrophs, especially Trichodesmium, are predicted to be limited by Fe, light, P or none of these factors, the boundaries of these regions are uncertain. Empirical validation of the models requires field surveys that are difficult to conduct without a rapid diagnostic for Fe or P limitation. Two PIs from the University of Southern California have identified several diagnostic genes for Fe and P limitation that are useful for quickly assessing the Fe and P status with natural Trichodesmium populations in space and time. These genes can also provide insights into the mechanism of Fe uptake. For instance, one of the Fe stress-induced genes is feoB which is predicted to be required for efficient uptake of Fe(II). Although common in facultatively anaerobic bacteria, its presence in open-ocean cyanobacteria is limited to Trichodesmium and another diazotroph, Crocosphaera. The PIs hypothesize that because diazotrophs have a higher Fe requirement due to N2 fixation than other cyanobacteria, they may utilize feoB, perhaps in conjunction with an exogenous or endogenous reductase mechanism, to access additional reservoirs of Fe within the dissolved Fe pool in seawater.The PIs will study the expression of Fe and P diagnostic probes within the western Pacific warm pool to determine if Trichodesmium is Fe or P limited in this region. On an already funded cruise from New Zealand to Hawaii in 2007, they anticipate encountering significant Fe gradients along N-S and E-W transects that span the range over which Trichodesmium becomes Fe-limited. Measurements of Fe and Fe-speciation will be made, including application of novel methods to extend current detection limits for Fe speciation to sub-nanomolar levels. Temporal aspects of the relationship between Fe speciation parameters and the Fe stress diagnostics will also be studied by following the characteristic Trichodesmium abundance maximum at the Hawaii Ocean Time Series Station (HOT) that occurs in the late summer.One component of the Broader Impacts of this proposal is the validation of current global ocean model predictions. This project will also develop a large dataset of Fe concentration measurements in an important, yet understudied regime of the ocean. Furthermore, this project will fund the research for two graduate students and include the participation of undergraduates from small, 4-year colleges on cruises.