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

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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.