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In partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Biology
In the
School of Biological Sciences
Juan P Barraza
Will defend his dissertation
Quantitative characterization of microbial communities
micro-biogeography during infectious disease.
Wednesday September 22nd, 2021
1 PM
https://bluejeans.com/462146884/0639
Thesis Advisor:
Marvin Whiteley, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Committee Members:
Sam Brown, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Brian Hammer, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
William Ratcliff, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Peter Yunker, Ph.D.
School of Physics
Georgia Institute of Technology
ABSTRACT:
Spatial structure, the arrangement of organisms in space, is an essential feature of life. It provides a mechanism for speciation, promotes niche development and shapes community function. The spatial structure of communities of animals and plants has been thoroughly characterized, but that of microbial communities, which impact many aspects of life including human health, is poorly understood. Interactions between microbes within a community during infection often result in increased tolerance to antibiotics and worse clinical outcomes. My thesis draws upon techniques from molecular biology, fluorescence microscopy, community ecology and computer science to build a framework to quantitatively characterize the spatial structure of microbial communities at the micron scale and aims to characterize bacterial interactions during infection and their impact on human health.
Interactions can be broadly classified as competitive or cooperative, and I use two different infection models to explore each one. To observe the impact competitive interactions, I use a model community of P. aeruginosa and S. aureus in a mouse chronic wound infection model. These two microbes co-exist in many infections, but most of their characterized interactions involve growth inhibition and killing. To observe the impact of cooperative interactions, I use S. gordonii and A. actinomycetemcomitans in a mouse abscess model. These two microbes co-exist in the oral cavity and abscesses, and exchange nutrients, including lactate, to grow more effectively. We collected images of these bacterial communities during infection and identified how interactions within microbial communities can impact the aggregation, abundance, and distribution in space of its members. Specifically, P. aeruginosa-secreted antimicrobial HQNO increases the number of planktonic cells in S. aureus and increases the micron-scale enrichment distance between these two microbes. We also show that lactate released by S. gordonii reduces the micron-scale enrichment distance between S. gordonii and A. actinomycetemcomitans. Overall, this works focused on developing tools for the exploration of micron-scale spatial structure and its impact on bacterial physiology during infection.
