Modern carbonate tufa towers in the alkaline (~pH 9.5) Big Soda Lake (BSL), Nevada, exhibit rapid precipitation rates (exceeding 3 cm/year) and host diverse microbial communities. Geochemical indicators reveal that carbonate precipitation is, in part, promoted by the mixing of calcium-rich groundwater and carbonate-rich lake water, such that a microbial role for carbonate precipitation is unknown. Here, we characterize the BSL microbial communities and evaluate their potential effects on carbonate precipitation that may influence fast carbonate precipitation rates of the active tufa mounds of BSL. Small subunit rRNA gene surveys indicate a diverse microbial community living endolithically, in interior voids, and on tufa surfaces. Metagenomic DNA sequencing shows that genes associated with metabolisms that are capable of increasing carbonate saturation (e.g., photosynthesis, ureolysis, and bicarbonate transport) are abundant. Enzyme activity assays revealed that urease and carbonic anhydrase, two microbial enzymes that promote carbonate precipitation, are active in situ in BSL tufa biofilms, and urease also increased calcium carbonate precipitation rates in laboratory incubation analyses. We propose that, although BSL tufas form partially as a result of water mixing, tufa-inhabiting microbiota promote rapid carbonate authigenesis via ureolysis, and potentially via bicarbonate dehydration and CO₂ outgassing by carbonic anhydrase. Microbially induced calcium carbonate precipitation in BSL tufas may generate signatures preserved in the carbonate microfabric, such as stromatolitic layers, which could serve as models for developing potential biosignatures on Earth and elsewhere.

中文翻译：

---

微生物尿素分解在碳酸盐凝灰岩堆快速形成中的潜在作用

内华达州碱性 (~pH 9.5) 大苏打湖 (BSL) 中的现代碳酸盐凝灰岩塔表现出快速的降水速率（超过 3 厘米/年）并拥有多种微生物群落。地球化学指标显示，碳酸盐沉淀部分是由富含钙的地下水和富含碳酸盐的湖水混合促进的，因此微生物对碳酸盐沉淀的作用尚不清楚。在这里，我们对 BSL 微生物群落进行了表征，并评估了它们对碳酸盐沉淀的潜在影响，这可能会影响 BSL 活性凝灰岩丘的快速碳酸盐沉淀速率。小亚基 rRNA 基因调查表明，一个多样化的微生物群落生活在内部、内部空隙和凝灰岩表面。宏基因组 DNA 测序表明，与能够增加碳酸盐饱和度的新陈代谢（例如，光合作用、尿素分解和碳酸氢盐转运）相关的基因非常丰富。酶活性测定表明，脲酶和碳酸酐酶这两种促进碳酸盐沉淀的微生物酶具有活性在实验室孵化分析中，原位BSL 凝灰岩生物膜和脲酶也增加了碳酸钙沉淀率。我们提出，尽管 BSL 凝灰岩部分是由于水混合而形成的，但居住在凝灰岩中的微生物群通过尿素分解促进碳酸盐的快速自生，并可能通过碳酸酐酶的碳酸氢盐脱水和 CO ₂脱气来促进碳酸盐自生。BSL 凝灰岩中微生物诱导的碳酸钙沉淀可能会产生保存在碳酸盐微结构中的特征，例如叠层石层，这可以作为在地球和其他地方开发潜在生物特征的模型。