Life in an Ultra-basic and Ultra-reducing Setting: The Cedars Serpentinization Communities

该项目的重点是雪松橄榄岩，这是北加州的一个地点，在那里发生了活跃的蛇纹岩作用，导致泉水如此极端，以至于目前的微生物代谢模式与那里存在的生命不兼容。因此，这项工作的智力驱动力围绕着对微生物如何在这个极端的无机世界中生存的理解，这个世界由超碱性（pH ~ 12）水组成，具有：1)低水平的有机碳，适合异养生长；2)（在这个pH值下）几乎没有溶解的二氧化碳或碳酸氢盐用于自养碳吸收；3) Eh通常低于- 550mv；4)没有明显丰富的电子受体；5)低水平的Na+。H+的缺乏和Na+的低浓度表明，在这种环境中存在的微生物具有与之前描述的可能不同的能量代谢。因此，识别和描述常驻微生物及其利用的代谢方法可能使我们对微生物（个体和/或共生群体）如何利用乍一看不可能不适合居住的环境形成理解。研究人员将研究几个不同的高pH池的微生物学，在为期两年的项目中，目标如下：1)通过16S rDNA鉴定和宏基因组测序鉴定优势微生物物种；2)利用宏基因组学和基因组组装技术表征环境和生物体基因含量；3)通过超转录组学确定这些基因中的哪些表达和/或活跃，以及4)对这些位点进行地球化学表征，以便将生物数据置于地球化学背景中。这种方法是为了测试哪些菌株在这种恶劣的生态系统中生长，以及它们是如何做到这一点（即，利用哪种代谢机制和途径）而产生假设的必要的第一步。它还涉及到一个问题，即究竟是基因含量还是物种含量（或两者都有）真正定义了一个成功的生态系统。该项目将导致鉴定在这种恶劣环境中生存和生长所需的基因类型：例如，细胞色素，atp酶，氢化酶，阳离子泵等。初步结果显示优势种数量较多，多样性很低。16S rRNA基因序列分析的结果表明，这些微生物与以前看到的任何微生物都不同，考虑到这些部位的代谢挑战，这也许并不奇怪。这项工作的结果也将为当今地球上微生物生命的适应和进化提供见解，并且考虑到这些超碱性，厌氧环境与光合作用活动之前的早期地球条件非常相似，这些结果可能对早期地球生命的适应和进化具有重要意义。因此，研究人员期望这些结果不仅对极端微生物（这些数据可能为理解一种新型碱性微生物群落提供一个里程碑）有更大的帮助，而且对早期地球生命模型也有很大的帮助。该项目将包括实地和实验室工作，将由一名博士后、一名研究生和几名本科生进行。

This project focuses on The Cedars Peridotite, a site in Northern California where active serpentinization occurs, resulting in spring waters so extreme that no current paradigms of microbial metabolism are compatible with life existing there. The intellectual driver of the work thus revolves around the understanding of how microbes manage to eke out a living in this extreme inorganic world of ultra-basic (pH ~ 12) water that has: 1) low levels of organic carbon for heterotrophic growth; 2) (at this pH) virtually no dissolved CO2 or bicarbonate for autotrophic carbon uptake; 3) an Eh that is routinely lower than -550 mV; 4) no obvious abundant electron acceptors; and, 5) low levels of Na+. The absence of H+ and the low concentration of Na+ suggest that the microbes present in this environment are equipped with an energy metabolism that is potentially unlike anything previously described. Thus, identifying and characterizing the resident microbes and the metabolic approaches they utilize may allow us to form an understanding for just how microbes (individuals and/or syntrophic groups) can exploit an environment that appears, at first glance, to be impossibly inhospitable. Investigators will study the microbiology of several different high pH pools, with the following goals in the two year project: 1) the identification of the dominant microbial species by 16S rDNA characterization and metagenomic sequencing; 2) the characterization of the environmental and organismal gene content by metagenomics and genome assembly; 3) the determination of which of these genes are expressed and/or active by metatranscriptomics, and, 4) the geochemical characterization of the sites, so that the biological data can be placed in a geochemical context. This approach is a necessary first step towards hypothesis generation in terms of testing which strains grow in this harsh ecosystem, and how they do it (i.e., which metabolic mechanisms and pathways are utilized). It also relates to the question of whether it is the gene content or the species content (or both) that truly defines a successful ecosystem. This project should lead to the identification of the types of genes required for survival and growth in this harsh environment: e.g., cytochromes, ATPases, hydrogenases, cation pumps, etc. Preliminary results have revealed a number of dominant species and very low diversity. Results of 16S rRNA gene sequence analyses suggest that these microbes are distinct from any previously seen microbes, perhaps not surprising, given the metabolic challenges in these sites. The results of this work will also provide insight into the adaptation and evolution of microbial life on present-day Earth, and given that these ultra-basic, anaerobic environments are close analogs to the early earth conditions prior to photosynthetic activity, the results may have significance regarding the adaptation and evolution of life on the early Earth. Investigators thus expect these results to significantly contribute to a greater understanding not only of extremophiles (the data may provide a milestone in terms of understanding a new type of alkaline microbial community), but to models of early earthly life. The project, which will include both field and laboratory work, will be carried out by a postdoctoral fellow, a graduate student, and several undergraduates.