Microbial mat communities are associated with extensive (~700 km²) and morphologically variable carbonate structures, termed microbialites, in the hypersaline Great Salt Lake (GSL), Utah. However, whether the composition of GSL mat communities co-varies with microbialite morphology and lake environment is unknown. Moreover, the potential adaptations that allow the establishment of these extensive mat communities at high salinity (14-17% total salts) are poorly understood. To address these questions, microbial mats were sampled from seven locations in the south arm of GSL representing different lake environments and microbialite morphologies. Despite the morphological differences, microbialite-associated mats were taxonomically similar and were dominated by the cyanobacterium Euhalothece and several heterotrophic bacteria. Metagenomic sequencing of a representative mat revealed Euhalothece and subdominant Thiohalocapsa populations that encode the Calvin cycle and nitrogenase, suggesting they supply fixed carbon and nitrogen to heterotrophic bacteria. Fifteen of the next sixteen most abundant taxa are inferred to be aerobic heterotrophs and surprisingly encode reaction center, rhodopsin, and/or bacteriochlorophyll biosynthesis proteins, suggesting aerobic photoheterotrophic (APH) capabilities. Importantly, proteins involved in APH are enriched in the GSL community relative to microbialite mat communities from lower salinity environments. These findings indicate that the ability to integrate light into energy metabolism is a key adaptation allowing for robust mat development in the hypersaline GSL.

IMPORTANCE

The earliest evidence of life on Earth is from organosedimentary structures, termed microbialites, preserved in 3.481 Ga rocks. Phototrophic microbial mats form in association with ~700 km² expanse of morphologically diverse microbialites in the hypersaline Great Salt Lake, Utah. Here we show taxonomically similar microbial mat communities are associated with morphologically diverse microbialites across the lake. Metagenomic sequencing reveals an abundance and diversity of autotrophic and heterotrophic taxa capable of harvesting light energy to drive metabolism. The unexpected abundance of and diversity in, the mechanisms of harvesting light energy observed in GSL mat populations likely functions to minimize niche overlap among co-inhabiting taxa, provide a mechanism(s) to increase energy yield and osmotic balance during salt stress, and enhance fitness. Together, these physiological benefits promote the formation of robust mats that, in turn, influence the formation of morphologically diverse microbialite structures that can be imprinted in the rock record.

在犹他州的高盐大盐湖（GSL）中，微生物垫群落与广泛的（〜700 km ²）和形态可变的碳酸盐结构（称为微生物岩）有关。但是，尚不清楚GSL垫群落的组成是否随微辉石形态和湖泊环境而变化。此外，人们对可能以高盐度（总盐含量为14-17％）建立这些广泛的垫群落的潜在适应性知之甚少。为了解决这些问题，从GSL南臂的七个位置取样了微生物垫，这些垫代表了不同的湖泊环境和微辉石形态。尽管在形态上有所不同，但与微生物相结合的垫在分类学上是相似的，并且主要由蓝藻Euhalothece主导。和几种异养细菌。代表性垫子的元基因组测序揭示了Euhalothece和主要的Thiohalocapsa编码加尔文循环和固氮酶的种群表明它们向异养细菌提供了固定的碳和氮。在接下来的16个最丰富的分类单元中，有15个被推断为有氧异养菌，并出人意料地编码了反应中心，视紫红质和/或细菌叶绿素生物合成蛋白，表明有氧光异养（APH）能力。重要的是，相对于来自较低盐度环境的微辉石垫群落，涉及APH的蛋白质在GSL群落中富集。这些发现表明，将光整合到能量代谢中的能力是关键的适应性，从而使高盐GSL中的垫层得以稳健发展。

重要性

地球上生命的最早证据来自保存在3.481 Ga岩石中的有机沉积结构，称为微恶岩。约700 km ²形成光养微生物垫高盐大盐湖，犹他州的形态多样的微生物。在这里，我们显示出与生物分类相似的微生物垫群落与整个湖中形态多样的微生物。元基因组测序揭示了自养和异养类群的丰富多样，能够收集光能来驱动新陈代谢。在GSL垫子种群中观察到的收集光能的意想不到的丰富性和多样性可能起到了使同居生物群之间的生态位重叠最小化的作用，提供了在盐胁迫期间增加能量产量和渗透平衡的机制，并增强了健身。这些生理上的好处共同促进了结实的垫子的形成，继而，