In nature, bacteria exist as members of communities in which cells respond to signals from each other and the environment. Microbial communities impact global processes like cycling of elements between soil, water, and air, and primary productivity of the oceans; they impact ecosystems and all the organisms that inhabit them. Limited understanding of how microbes control complex behaviors in response to each other and their environment impedes our ability to harness them for pollution and climate control, and for increased bioenergy and food production. Understanding how bacteria integrate signals and respond appropriately is a fundamental challenge of great practical significance. Manipulation of microbial communities to improve life and solve global problems will depend on knowledge of how bacteria interact with each other and their environment. To advance knowledge of how thousands of Myxococcus xanthus bacteria interact with each other and their environment, experimental and mathematical modeling methods will be used to better understand the biochemical switch which controls spore formation. Undergraduate and graduate students, and a postdoctoral scholar will receive interdisciplinary research training as a result of this project, and there will be outreach to non-scientists through presentations to 5th grade females, participation in the MSU Science Festival, and an informal Science Café-style seminar series involving local high schools.
Myxococcus xanthus provides an attractive experimental system. When starved, cells change their gene expression and metabolism, send signals to each other, alter their movements to construct multicellular mounds (nascent fruiting bodies), and some of the rod-shaped cells differentiate into spherical, dormant spores. Other cells remain outside of fruiting bodies as peripheral rods and the majority of cells undergo lysis. Previous work funded by the National Science Foundation focused on understanding how genes are regulated in response to C-signaling during fruiting body development. C-signaling involves CsgA, a protein that becomes associated with the cell surface and mediates short-range signaling between cells. C-signaling regulates not only gene expression, but cell movements, lysis, and sporulation. Several C-signal-dependent promoters were discovered to be under combinatorial control of two transcription factors, MrpC and FruA. Recently, one such promoter was found to drive transcription of devT, whose product positively regulates mrpC. Since MrpC activates transcription of fruA, the three proteins form a network. Understanding how this network integrates multiple signals and governs multiple behaviors during M. xanthus development is a formidable challenge requiring systems analysis, including modeling and synthetic biology approaches like rewiring the naturally occurring network. The central hypothesis to be tested is that the MrpC-FruA-DevT (MFD) network integrates the starvation and C-signals, functioning as a biochemical switch (or part of the switch) that governs commitment to spore formation. To address this hypothesis, the following aims are proposed: 1) measure dynamical changes in the MFD network components and output before and during commitment of wild type and mutants, and use the data to build a mathematical model of the MFD network, 2) use the model to explore whether the network can operate as a switch that becomes irreversible and test this by measuring MFD network dynamics after addition of nutrients to developing cells, 3) use the model to explore if the MFD network can achieve an ultrasensitive response and test this by measuring MFD network response as a function of added C-signal or nutrients, and 4) construct synthetically rewired MFD networks, measure their dynamical responses, and analyze the results using mathematical models of rewired networks.
