DISSERTATION RESEARCH: A trait-based approach to characterize microbial community composition

最令人惊讶的科学发现之一是细菌和其他微生物在人类和环境生物学中发挥的关键作用。这些小生物体决定了所有生命所必需的营养的可获得性。然而，关于影响微生物生活在哪里的因素，或者它们如何协同工作以提供生命的基本需求，人们知之甚少。该项目将确定温度、水、出生、死亡和运动等因素对自然微生物群落的大小、位置和组成的重要性。它专注于循环氮的微生物，氮是一种对全球动植物和人类健康至关重要的营养物质。该项目将促进博士生在现代科学技术及其在自然社区中的应用方面的教育和培训。结果有可能改善农业和工业产出以及人类健康。它们将通过教育媒体和加州州立公园的演示文稿被翻译给普通公众。研究人员将通过奥兰治县发现立方体科学中心向当地社区展示他们的研究成果，该中心是一个非营利性组织，旨在通过科学教育激励公民。本项目将调查确定性与随机性力量对微生物群落组成和功能变化的贡献。将检验两个假设：1)功能基因多样性的随机变异将低于微生物分类多样性的随机变异；2)较少分类群执行的功能的随机变异(如固氮)将高于许多分类群执行的功能的随机变异(如氨同化)。确定性变异性源于理论上可预测的因素，如降水或养分可获得性。相反，随机性主要通过漂移影响多样性，而漂移又受扩散的影响。该项目将使用装满植物垃圾的袋子来复制自然微生物群落。交叉实验设计将操纵一种已知的确定性效应(环境降水与附加降水)和扩散(对移民开放与关闭)。对于初始接种，每袋三个重复样本将产生元基因组。然后，这些关于微生物群落的遗传信息将在处理内和处理间进行比较，着眼于分类组成和功能基因，重点是氮循环。这些结果将极大地促进目前对影响自然微生物群落的主要因素的理解。

One of the most surprising scientific discoveries is the critical role that bacteria and other microbes play in human and environmental biology. These small organisms determine the availability of nutrients that are essential to all life. Little is known about the factors that influence where microbes live, however, or how they work together to provide life's basic needs. This project will determine the importance of factors such as temperature, water, birth, death, and movement to the size, location, and composition of natural microbial communities. It focuses on microbes that cycle nitrogen, a nutrient that is critical for plant, animal, and human health across the globe. The project will advance the education and training of a doctoral student in modern scientific techniques and their application to natural communities. Results have the potential to improve agriculture and industrial output as well as human health. They will be translated to the general public through educational media and presentations at a California state park. The investigators will present their research to local communities through the Discovery Cube Science Center of Orange County, a non-profit organization with a goal to inspire citizens through science education. This project will investigate the contribution of deterministic versus stochastic forces to variation in microbial community composition and function. Two hypotheses will be tested: 1) Stochastic variation of functional gene diversity will be lower than that of microbial taxonomic diversity and 2) Stochastic variation of functions carried out by fewer taxa (narrow functions such as nitrogen fixation) will be higher than stochastic variation of functions carried out by many taxa (broad functions such as ammonia assimilation). Deterministic variability derives from theoretically predictable factors such as precipitation or nutrient availability. In contrast, stochasticity affects diversity mainly through drift, which is in turn influenced by dispersal. This project will use bags filled with plant litter to replicate natural microbial communities. A crossed experimental design will manipulate a known, deterministic effect (ambient versus added precipitation) and dispersal (open versus closed to immigration). Metagenomes will be generated from three replicate samples per bag and for the initial inoculum. This genetic information about the microbial community will then be compared within and across treatments, looking both at taxonomic composition and functional genes, with a focus on the nitrogen cycle. Results will significantly advance current understanding of the primary factors affecting natural microbial communities.