Unicellular methanotrophs are a widespread, polyphyletic group of organisms that oxidize methane to assimilate carbon and obtain energy. Methanotrophs are of interest to astrobiologists given their prevalence in terrestrial environmental niches, like geothermal hot springs and hydrothermal vents, that are homologs for proposed extraterrestrial targets. Recent research demonstrates that light rare earth elements are required for the catalytic activity of the common xoxF isoform of methanol dehydrogenase, an enzyme in the aerobic methanotrophy pathway whose main isoform, mxa-MeDH, in contrast uses a calcium ion for catalysis. Although rare earth elements exist in picomolar concentrations in the ocean, the gene for xoxF is maintained in marine methanotrophs, pointing to a possible terrestrial origin for aerobic methanotrophy. Here we present a multi-season time series of rare earth element concentrations from autumn 2018 in the oligotrophic Sargasso Sea, and an initial analysis of molecular markers for aerobic methanotrophy in summer 2019. We observe a repeated depletion of light rare earth elements relative to heavy rare earth elements in the upper water column, between approximately 200 m and 500 m. This feature was collocated with observations of microbial growth on media with methanol as a sole carbon source, and detection of the xoxF5 gene. We aim to determine if aerobic methanotrophs generate a reproducible and identifiable signal through the selective uptake of light rare earth elements over heavier REEs that could be recorded in the geologic record indicating past aerobic methanotrophy.

单细胞甲烷营养生物是一种广泛的，多系生物群，可以将甲烷氧化以吸收碳并获取能量。甲烷营养生物引起了天体生物学家的兴趣，因为它们在诸如地热温泉和热液喷口这样的陆地环境生态位中普遍存在，而这些生态位与拟议的地球外目标是同源的。最新研究表明，轻质稀土元素对于甲醇脱氢酶的常见xoxF同工型具有催化活性，甲醇脱氢酶是有氧甲烷营养代谢途径中的一种酶，而其主要同工型mxa-MeDH相反使用钙离子进行催化。尽管海洋中的皮摩尔浓度存在稀土元素，但xoxF的基因仍存在于海洋甲烷营养体中，这表明有氧甲烷营养体可能是地球起源。在这里，我们介绍了贫营养性Sargasso海中从2018年秋季开始的多季节时间序列的稀土元素浓度，并初步分析了2019年夏季有氧甲烷代谢的分子标记。我们观察到轻稀土元素相对重元素的反复消耗上部水柱中大约200 m至500 m之间的稀土元素。此功能与观察微生物在以甲醇为唯一碳源的培养基上生长以及对微生物的检测相一致。在大约200 m和500 m之间。此功能与以甲醇为唯一碳源的培养基上微生物生长的观察值并检测到 在大约200 m和500 m之间。此功能与观察微生物在以甲醇为唯一碳源的培养基上生长以及对微生物的检测相一致。xoxF5基因。我们旨在确定好氧甲烷氧化菌是否通过选择性摄取较重稀土元素的轻稀土元素而产生可再现且可识别的信号，而稀土元素可能记录在地质记录中，表明过去的好氧甲烷氧化作用。