SETI Institute, Mountain View, California 94043, USA.
Astrobiology. 2009 Nov;9(9):875-93. doi: 10.1089/ast.2008.0325.
Actively forming gypsum deposits at the Guerrero Negro sabkha and saltern system provided habitats for stratified, pigmented microbial communities that exhibited significant morphological and phylogenetic diversity. These deposits ranged from meter-thick gypsum crusts forming in saltern seawater concentration ponds to columnar microbial mats with internally crystallized gypsum granules developing in natural anchialine pools. Gypsum-depositing environments were categorized as forming precipitation surfaces, biofilm-supported surfaces, and clastic surfaces. Each surface type was described in terms of depositional environment, microbial diversity, mineralogy, and sedimentary fabrics. Precipitation surfaces developed in high-salinity subaqueous environments where rates of precipitation outpaced the accumulation of clastic, organic, and/or biofilm layers. These surfaces hosted endolithic biofilms comprised predominantly of oxygenic and anoxygenic phototrophs, sulfate-reducing bacteria, and bacteria from the phylum Bacteroidetes. Biofilm-supported deposits developed in lower-salinity subaqueous environments where light and low water-column turbulence supported dense benthic microbial communities comprised mainly of oxygenic phototrophs. In these settings, gypsum granules precipitated in the extracellular polymeric substance (EPS) matrix as individual granules exhibiting distinctive morphologies. Clastic surfaces developed in sabkha mudflats that included gypsum, carbonate, and siliclastic particles with thin gypsum/biofilm components. Clastic surfaces were influenced by subsurface brine sheets and capillary evaporation and precipitated subsedimentary gypsum discs in deeper regions. Biofilms appeared to influence both chemical and physical sedimentary processes in the various subaqueous and subaerially exposed environments studied. Biofilm interaction with chemical sedimentary processes included dissolution and granularization of precipitation surfaces, formation of gypsum crystals with equant and distorted habits, and precipitation of trace carbonate and oxide phases. Fine-scale wrinkle structures visible in clastic surfaces of sabkha environments offered evidence of the biofilm's role in physical sedimentary processes. These findings are highly relevant to astrobiology because they expand and refine the known characteristics of gypsum deposits, including their biological components.
在格雷罗内格罗萨布哈和盐田系统中积极形成石膏沉积物，为分层、有色素的微生物群落提供了栖息地，这些微生物群落表现出显著的形态和系统发育多样性。这些沉积物的范围从在盐田海水浓缩池形成的数米厚的石膏壳到在天然泻湖的柱状微生物垫内结晶的石膏颗粒。形成石膏的环境分为形成沉淀表面、生物膜支撑表面和碎屑表面。每种表面类型都根据沉积环境、微生物多样性、矿物学和沉积结构进行了描述。沉淀表面在高盐度水下环境中形成，在这些环境中，沉淀的速度超过了碎屑、有机和/或生物膜层的积累。这些表面上有内生生物膜，主要由需氧和厌氧光合生物、硫酸盐还原菌和厚壁菌门的细菌组成。生物膜支撑的沉积物在低盐度水下环境中形成，在这些环境中，光和低水层湍流支持密集的底栖微生物群落，主要由需氧光合生物组成。在这些环境中，石膏颗粒在细胞外聚合物（EPS）基质中沉淀为具有独特形态的单个颗粒。碎屑表面在盐沼泥滩上形成，包括石膏、碳酸盐和硅质碎屑颗粒，以及薄的石膏/生物膜成分。碎屑表面受地下卤水层和毛细蒸发的影响，并在较深的区域沉淀亚沉积石膏盘。生物膜似乎影响了研究中各种水下和暴露于空气中的环境中的化学和物理沉积过程。生物膜与化学沉积过程的相互作用包括沉淀表面的溶解和颗粒化、形成等轴和变形习性的石膏晶体以及痕量碳酸盐和氧化物相的沉淀。在盐沼环境碎屑表面可见的细微褶皱结构为生物膜在物理沉积过程中的作用提供了证据。这些发现与天体生物学密切相关，因为它们扩展和完善了已知的石膏沉积物特征，包括其生物成分。
