College of Marine Science, University of South Florida, Florida 33701, USA.
Astrobiology. 2012 Jul;12(7):685-98. doi: 10.1089/ast.2011.0812. Epub 2012 Aug 10.
Microbialites are biologically mediated carbonate deposits found in diverse environments worldwide. To explore the organisms and processes involved in microbialite formation, this study integrated genomic, lipid, and both organic and inorganic stable isotopic analyses to examine five discrete depth horizons spanning the surface 25 mm of a modern freshwater microbialite from Cuatro Ciénegas, Mexico. Distinct bacterial communities and geochemical signatures were observed in each microbialite layer. Photoautotrophic organisms accounted for approximately 65% of the sequences in the surface community and produced biomass with distinctive lipid biomarker and isotopic (δ(13)C) signatures. This photoautotrophic biomass was efficiently degraded in the deeper layers by heterotrophic organisms, primarily sulfate-reducing proteobacteria. Two spatially distinct zones of carbonate precipitation were observed within the microbialite, with the first zone corresponding to the phototroph-dominated portion of the microbialite and the second zone associated with the presence of sulfate-reducing heterotrophs. The coupling of photoautotrophic production, heterotrophic decomposition, and remineralization of organic matter led to the incorporation of a characteristic biogenic signature into the inorganic CaCO(3) matrix. Overall, spatially resolved multidisciplinary analyses of the microbialite enabled correlations to be made between the distribution of specific organisms, precipitation of carbonate, and preservation of unique lipid and isotopic geochemical signatures. These findings are critical for understanding the formation of modern microbialites and have implications for the interpretation of ancient microbialite records.
微生物岩是在全球各种环境中发现的生物介导的碳酸盐沉积物。为了探索参与微生物岩形成的生物和过程，本研究综合了基因组、脂质以及有机和无机稳定同位素分析，研究了来自墨西哥 Cuatro Ciénegas 的现代淡水微生物岩的 5 个不同深度层，这些深度层跨越了表面 25mm。在每个微生物岩层中都观察到了独特的细菌群落和地球化学特征。光自养生物约占表面群落中序列的 65%，并产生具有独特脂质生物标志物和同位素（δ(13)C）特征的生物量。这种光自养生物量在更深的层中被主要为硫酸盐还原菌的异养生物有效地降解。在微生物岩内观察到两个空间上不同的碳酸盐沉淀区，第一区与微生物岩中光自养部分相对应，第二区与硫酸盐还原异养生物的存在有关。光自养生产、异养分解和有机质的再矿化的耦合作用导致了特征生物成因特征被纳入无机 CaCO(3)基质中。总的来说，对微生物岩的空间分辨多学科分析使得可以在特定生物的分布、碳酸盐的沉淀以及独特的脂质和同位素地球化学特征的保存之间建立相关性。这些发现对于理解现代微生物岩的形成至关重要，并对古代微生物岩记录的解释具有重要意义。
