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所起的关键作用。这些小生物决定了所有生命所必需的营养物质的可用性。然而，人们对影响微生物生存环境的因素知之甚少，也不知道它们是如何协同工作以提供生命的基本需求的。该项目将确定温度、水、出生、死亡和移动等因素对天然微生物群落的大小、位置和组成的重要性。它专注于氮循环的微生物，氮是一种对全球植物、动物和人类健康至关重要的营养物质。该项目将促进现代科学技术及其在自然群落中的应用方面博士生的教育和培训。研究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在加州州立公园的演讲被翻译给公众。研究人员将通过奥兰治县的探索立方科学中心向当地社区展示他们的研究成果，这是一个旨在通过科学教育激励公民的非营利组织。该项目将研究确定性与随机力对微生物群落组成和功能变化的贡献。本文将验证两个假设：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)少数分类群（如固氮等狭窄功能）的功能随机变异将高于许多分类群（如氨同化等广泛功能）的功能随机变异。确定性变率源于理论上可预测的因素，如降水或养分有效性。随机性主要通过漂移影响多样性，而漂移又受扩散的影响。这个项目将使用装满植物凋落物的袋子来复制自然微生物群落。交叉实验设计将操纵已知的确定性效应（环境与增加的降水）和扩散（开放与封闭的移民）。宏基因组将从每袋和初始接种的三个重复样本中产生。这些关于微生物群落的遗传信息将在处理内部和不同处理之间进行比较，研究分类组成和功能基因，重点关注氮循环。研究结果将显著促进目前对影响天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.