Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL, USA.
Biosciences Division, Argonne National Laboratory, Argonne, IL, USA.
Geobiology. 2018 May;16(3):319-337. doi: 10.1111/gbi.12283. Epub 2018 Apr 15.
Laguna Bacalar is a sulfate-rich freshwater lake on the Yucatan Peninsula that hosts large microbialites. High sulfate concentrations distinguish Laguna Bacalar from other freshwater microbialite sites such as Pavilion Lake and Alchichica, Mexico, as well as from other aqueous features on the Yucatan Peninsula. While cyanobacterial populations have been described here previously, this study offers a more complete characterization of the microbial populations and corresponding biogeochemical cycling using a three-pronged geobiological approach of microscopy, high-throughput DNA sequencing, and lipid biomarker analyses. We identify and compare diverse microbial communities of Alphaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria that vary with location along a bank-to-bank transect across the lake, within microbialites, and within a neighboring mangrove root agglomeration. In particular, sulfate-reducing bacteria are extremely common and diverse, constituting 7%-19% of phylogenetic diversity within the microbialites, and are hypothesized to significantly influence carbonate precipitation. In contrast, Cyanobacteria account for less than 1% of phylogenetic diversity. The distribution of lipid biomarkers reflects these changes in microbial ecology, providing meaningful biosignatures for the microbes in this system. Polysaturated short-chain fatty acids characteristic of cyanobacteria account for <3% of total abundance in Laguna Bacalar microbialites. By contrast, even short-chain and monounsaturated short-chain fatty acids attributable to both Cyanobacteria and many other organisms including types of Alphaproteobacteria and Gammaproteobacteria constitute 43%-69% and 17%-25%, respectively, of total abundance in microbialites. While cyanobacteria are the largest and most visible microbes within these microbialites and dominate the mangrove root agglomeration, it is clear that their smaller, metabolically diverse associates are responsible for significant biogeochemical cycling in this microbialite system.
拉古纳巴卡尔是尤卡坦半岛上的一个富含硫酸盐的淡水湖，拥有大型微生物岩。高硫酸盐浓度使拉古纳巴卡尔与墨西哥的皮坦湖和阿尔奇奇卡等其他淡水微生物岩地点以及尤卡坦半岛上的其他水态特征区分开来。虽然这里以前已经描述了蓝藻种群，但这项研究通过显微镜、高通量 DNA 测序和脂质生物标志物分析的三管齐下的地球生物学方法，更全面地描述了微生物种群及其相应的生物地球化学循环。我们确定并比较了沿湖两岸到两岸的横截面上、微生物岩内和附近红树林根系聚集体中不同的微生物群落，这些微生物群落包括α变形菌门、δ变形菌门和γ变形菌门。特别是硫酸盐还原菌非常普遍且多样，构成微生物岩内系统发育多样性的 7%-19%，据推测它们会显著影响碳酸盐沉淀。相比之下，蓝藻仅占系统发育多样性的不到 1%。脂质生物标志物的分布反映了微生物生态学的这些变化，为该系统中的微生物提供了有意义的生物特征。短链多不饱和脂肪酸是蓝藻的特征，占拉古纳巴卡尔微生物岩总丰度的<3%。相比之下，即使是归因于蓝藻和许多其他生物的短链和单不饱和短链脂肪酸，包括α变形菌门和γ变形菌门的许多类型，分别占微生物岩总丰度的 43%-69%和 17%-25%。虽然蓝藻是这些微生物岩中最大和最明显的微生物，并且主导红树林根系聚集体，但很明显，它们较小、代谢多样的同伴是这个微生物岩系统中重要生物地球化学循环的主要原因。
