EAGER: The Bacterial Magnetosome may be a Potential Energy-Harvesting Pseudo-organelle for Magnetotrophy

趋磁性细菌(MTB)进化出一套独特的遗传编码蛋白质，用于在称为磁小体的细胞内合成磁性晶体。传统的看法是，磁小体的功能就像一种内部罗盘，使这些细胞能够在MTB游过水体时，利用地球的磁场导航到它们理想的位置。虽然这是对趋磁性的一个很好的解释，但合成磁小体的高昂成本与MTB在自然界中罕见的排列之间的差异表明了另一种功能。这项提议将调查潜在的变革性假设，即磁小体不用于导航/定向，而是一种以前未知的新陈代谢形式的一部分。如果这一假设得到证实，那么这将为已建立的产生能量的途径(如自养和异养)增加一种完全不同的新陈代谢形式(磁营养)。这种新的新陈代谢形式实际上会广泛存在，因为几乎在任何有液态水的环境中都能发现结核杆菌，而这些细菌是在数十亿年前进化出来的。从这项研究中获得的知识将引起广泛学科范围的教育工作者的极大兴趣，并通过帮助解决生命科学和物理科学之间联系所不可或缺的基本问题来促进科学的进步。这些研究活动将促进对未被充分代表的少数族裔学生以及嵌入调查实验室的高中教师进行STEM培训。将进行实验，以测试磁小体是否在为结核分枝杆菌产生代谢能量方面发挥作用。定制的生长室将用于在一定的外部磁场强度范围内培养结核分枝杆菌。细菌样本将包括结核分枝杆菌的野生型菌株和缺乏合成其内部磁铁的遗传库的突变株。磁性测量将被用来确定磁小体的存在(或不存在)，并表征野生型细胞中内部磁铁矿的磁场强度。将通过吸光度测量、细胞计数、游泳速度和携带能量的分子的分析来监测细菌的生长和活动。组学和加入野生型和突变菌株的同位素标记化合物将使识别受磁场影响的基因网络和产品(蛋白质和代谢物)成为可能。整合来自这些不同但互补的实验的数据将允许仔细测试新的假设，即磁小体的进化是为了最大限度地吸收能量和/或在MTB经常占据的有机碳枯竭环境中生存。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Magnetotactic bacteria (MTB) have evolved a unique suite of genetically-encoded proteins that are used to synthesize magnetic crystals within an intracellular compartment called the magnetosome. The conventional wisdom is that the magnetosome functions as a sort of internal compass enabling these cells to navigate to their ideal niche using the Earth's magnetic field as MTB swim through bodies of water. While this is an elegant explanation for magnetotaxis, the disparity between the high cost of synthesizing the magnetosome and infrequent alignment of MTB in nature suggests another function. This proposal will investigate the potentially transformative hypothesis that the magnetosome is not used for navigation/orientation but rather it is part of a previously unknown form of metabolism. If this hypothesis is validated then this would add a radically different form of metabolism (magneto-trophy) to established pathways to generate energy like autotrophy and heterotrophy. This new form of metabolism would actually be widespread because MTB are found in just about any environment with liquid water and these bacteria evolved billions of years ago. Knowledge gained from this research will be of great interest to educators across broad disciplinary bounds and promote the progress of science by helping to address fundamental questions integral to the connection between life science and physical science. These research activities will promote STEM training for underrepresented minority students as well as high school teachers embedded in the investigators' labs. Experiments will be performed to test whether the magnetosome plays a role in generating metabolic energy for MTB. Custom-made growth chambers will be used to culture MTB under a range of external magnetic-field strengths. Bacteria specimens will include wild-type strains of MTB and mutants that lack the genetic repertoire to synthesize their internal magnets. Magnetic measurements will be used to determine the presence (or absence) of the magnetosome and characterize the field-strength of internal magnetite in wild-type cells. Bacteria growth and activity will be monitored through absorbance measurements, cell counts, swimming speed, and assays for energy-carrying molecules. Omics and incorporation of isotopically-labeled compounds for wild-type versus mutant strains will permit identification of gene networks and products (proteins and metabolites) impacted by magnetic fields. Integration of data from these distinct yet complementary experiments will allow to carefully test the novel hypothesis that the magnetosome evolved to maximize energy uptake and/or endure in organic-carbon depleted environments that MTB often occupy in nature.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.