Chemical signatures of magnetite produced by iron-metabolizing bacteria

磁铁矿晶体经常在古代海洋沉积岩中发现，如带状铁地层（BIF）或碳酸盐台地，有些年龄高达38亿年。磁铁矿可以通过非生物或生物途径产生。铁代谢细菌的活动被认为是在大部分地质记录中沉淀磁铁矿晶体的原因。然而，物理表征本身并没有提供一个明确的天然磁铁矿样品的生物起源的确定。因此，必须区分生物磁铁矿或生物磁铁矿与非生物磁铁矿的矿物学和化学性质。在这方面，我们建议表征由（1）Fe（III）-还原和（2）Fe（II）-氧化细菌产生的生物磁铁矿的微量元素组成。Fe（III）还原希瓦氏菌oneidensis菌株MR-1和Fe（II）氧化食酸菌属菌株BoFeN 1将在具有明确化学组成的培养基中培养。在生物磁铁矿合成过程中的微量元素的分配，即微量元素掺入到生物磁铁矿的特定模式，然后将被量化，并与非生物磁铁矿和先前研究的趋磁细菌产生的磁铁矿晶体进行比较。我们的目标是揭示不同的磁铁矿沉淀条件之间的不同分区模式，并因此，确定细菌代谢活动的潜在生物特征。我们进一步建议实验研究的命运，这种潜在的生物签名在成岩作用模拟磁铁矿泥化。最后，我们将把我们的实验结果与从前寒武纪BIF和碳酸盐岩中收集的天然磁铁矿样品的化学成分进行比较，最终目的是确定地球古代历史中是否存在产磁铁矿细菌。

Magnetite crystals are frequently found in ancient marine sedimentary rocks, such as banded iron formations (BIF) or carbonate platforms, some as old as 3.8 billion years. Magnetite can be produced through abiotic or biological pathways. The activity of iron-metabolizing bacteria has been proposed to be responsible for precipitation of magnetite crystals throughout much of the geological record. However, physical characterizations alone have not provided an unambiguous determination for the biological origin of natural magnetite samples. Therefore, it is imperative to discern the mineralogical and chemical properties of biogenic magnetite, or biomagnetite, from abiotic magnetite. In this regard, we propose to characterize the trace element composition of biomagnetite produced by (1) Fe(III)-reducing and (2) Fe(II)-oxidizing bacteria. The Fe(III)-reducing Shewanella oneidensis strain MR-1 and the Fe(II)-oxidizing Acidovorax sp. strain BoFeN1 will be cultivated in media with well-defined chemical composition. The partitioning of trace elements during biomagnetite syntheses, i.e. the specific pattern of trace element incorporation into the biomagnetite, will then be quantified and compared with abiotic magnetite and the previously studied magnetite crystals produced by magnetotactic bacteria. The goal is to uncover different partitioning patterns between the different conditions of magnetite precipitation, and as such, determine a potential biosignature of bacterial metabolic activity. We further propose to experimentally examine the fate of this potential biosignature during diagenesis to mimic magnetite fossilization. Finally, we will compare our experimental results with the chemical composition of natural magnetite samples collected from Precambrian BIF and carbonates with the ultimate aim being to ascertain the presence of magnetite-producing bacteria in Earths ancient history.