Pinto Gabriel A, Lezcano María Ángeles, Sanchéz-García Laura, Martínez Rodrigo, Parro Víctor, Carrizo Daniel
Institute of Natural Sciences, Geological Survey of Belgium, Brussels, Belgium.
Laboratoire G-Time, Université Libre de Bruxelles, Brussels, Belgium.
Astrobiology. 2025 Feb;25(2):115-132. doi: 10.1089/ast.2024.0071.
Chondritic meteorites can be appropriate substrates for the colonization of terrestrial microorganisms. However, determining whether organic compounds are intrinsic to the meteorite or come from external (terrestrial) contamination is still controversial. This research explores the molecular distribution and carbon isotopic composition of three lipid families (hydrocarbons, alkanoic acids, and alcohols) as well as DNA extracted from the interior of a CO carbonaceous chondrite named El Médano 464 (EM 464), discovered in the Atacama Desert in 2019. Three soil samples from the discovery area of EM 464 were collected and used as a background control for the composition and distribution of organic compounds. Our results revealed a higher abundance of the three lipid families in EM 464 compared with the surrounding soil samples. The organic compounds in EM 464 showed a mean δC value of -27.8 ± 0.5 for hydrocarbons ( = 20), -27.6 ± 1.1 for alkanoic acids ( = 17), and -27.5 ± 2.2‰ for alcohols ( = 18). These δC-depleted values are compatible with terrestrial biosignatures and are within isotopic values produced as a result of carbon fixation due to the Calvin cycle (δC of ca. from -19 to -34‰) widely used by photosynthetic terrestrial microorganisms. The DNA analysis (based on the bacterial 16S rRNA gene) showed a dominance of Proteobacteria (now Pseudomonadota) and Actinobacteriota in both meteorite and soils but exhibited different bacterial composition at the family level. This suggests that the microbial material inside the meteorite may have partially come from the adjacent soils, but we cannot rule out other sources, such as windborne microbes from distant locations. In addition, the meteorite showed higher bacterial diversity (H' = 2.4-2.8) compared with the three soil samples (H' = 0.3-1.8). Based on the distribution and δC value of organic compounds as well as DNA analysis, we suggest that most, if not all, of the organic compounds detected in the studied CO chondrite are of terrestrial origin (, contamination). The terrestrial contamination of EM 464 by a diverse microbial community indicates that Atacama chondrites can offer distinctive ecological conditions for microorganisms to thrive in the harsh desert environment, which can result in an accumulation of microbial biomass and preservation of molecular fossils over time.
球粒陨石可能是陆地微生物定殖的合适基质。然而，确定有机化合物是陨石固有的还是来自外部（陆地）污染仍然存在争议。本研究探索了三种脂质家族（烃类、链烷酸和醇类）以及从2019年在阿塔卡马沙漠发现的一块名为埃尔梅达诺464（EM 464）的CO碳质球粒陨石内部提取的DNA的分子分布和碳同位素组成。采集了来自EM 464发现区域的三个土壤样本，并将其用作有机化合物组成和分布的背景对照。我们的结果显示，与周围土壤样本相比，EM 464中这三种脂质家族的丰度更高。EM 464中的有机化合物，烃类的平均δC值为-27.8±0.5（n = 20），链烷酸为-27.6±1.1（n = 17），醇类为-27.5±2.2‰（n = 18）。这些贫δC值与陆地生物标志相符，且在光合陆地微生物广泛使用的卡尔文循环（δC约为-19至-34‰）导致的碳固定产生的同位素值范围内。DNA分析（基于细菌16S rRNA基因）表明，变形菌门（现假单胞菌门）和放线菌门在陨石和土壤中均占主导地位，但在科水平上表现出不同的细菌组成。这表明陨石内部的微生物物质可能部分来自相邻土壤，但我们不能排除其他来源，如来自遥远地点的风传微生物。此外，与三个土壤样本（H' = 0.3 - 1.8）相比，陨石显示出更高的细菌多样性（H' = 2.4 - 2.8）。基于有机化合物的分布和δC值以及DNA分析，我们认为在所研究的CO球粒陨石中检测到的大部分（如果不是全部）有机化合物是陆地来源的（即污染）。EM 464被多样的微生物群落进行陆地污染，这表明阿塔卡马球粒陨石可以为微生物在恶劣的沙漠环境中繁衍生息提供独特的生态条件，随着时间的推移，这可能导致微生物生物量的积累和分子化石的保存。
