Department of Physics

Faculty Description


Contact
  • Office Location:  
    Office: UH 7246
  • Office Phone:  858-534-7263
    Lab Phone: 858-534-5817
  • Email:  thwa@ucsd.edu
  • Administrative Contact:  Nancy Steinmetz
Research Statement
  • I am interested in a variety of complex phenomena that arise from competing interactions in systems involving a large number of microscopic degrees of freedom. These include, for example, the pinning of magnetic flux lines in disordered superconductors, the dynamics of interfaces in nonequilibrium growth phenomena, and the formation and recognition of complex patterns in chemical and biological systems. Various aspects of these phenomena are characterized by applying the methods of statistical physics and field theory, and by extending the existing knowledge of disordered and stochastic systems.
Awards & News
  • Honors and Awards
  • - Burroughs-Wellcome's Innovation Award in Functional Genomics, 2000-2003 Guggenheim Fellowship, 1999-2000.

    - Beckman Young Investigator Award, 1997-2000.

    - Office of Naval Research Young Investigator Award, 1995-1998.

    - A. P. Sloan Foundation Research Fellowship, 1994-1999.

    - Overseas Chinese Physics Association's Outstanding Young Researcher Award, 1993.

    - American Physical Society's LeRoy Apker Award, 1986
  • Physics and Quantitative Biology: identifying a simple genetic circuit for stripes
  • Many living things have stripes, but the developmental processes that create these and other patterns are complex and difficult to untangle.

    Now a team of scientists has designed a simple genetic circuit that creates a striped pattern that they can control by tweaking a single gene.

    With multiple starting points, bacteria guided by a simple genetic circuit can create intricate patterns.
    "The essential components can be buried in a complex physiological context," said Terence Hwa, a professor of physics at the University of California, San Diego, and one of the leaders of the study published October 14 in Science. "Natural systems make all kinds of wonderful patterns, but the problem is you never know what's really controlling it."

    With genes taken from one species of bacterium and inserted into another, Hwa and colleagues from the University of Hong Kong assembled a genetic loop from two linked modules that senses how crowded a group of cells has become and responds by controlling their movements.

    One of the modules secretes a chemical signal called acyl-homoserine lactone (AHL). As the bacterial colony grows, AHL floods the accumulating cells, causing them to tumble in place rather than swim. Stuck in the agar of their dish, they pile up.

    Because AHL doesn't diffuse very far, a few cells escape and swim away to begin the process again.

    Left to grow overnight, the cells create a target-like pattern of concentric rings of crowded and dispersed bacterial cells. By tweaking just one gene that limits how fast and far cells can swim, the researchers were able to control the number of rings the bacteria made. They can also manipulate the pattern by modifying how long AHL lasts before it degrades.


    A colony of bacteria with a "synthetic" genetic circuit develops a pattern of strips over 24 hours.
    Although individual bacteria are single cells, as colonies they can act like a multicellular organism, sending and receiving signals to coordinate the growth and other functions of the colony. That means fundamental rules that govern the development of these patterns could well apply to critical steps in the development of other organisms.

    To uncover these fundamental rules, Hwa and colleagues characterized the performance of their synthetic genetic circuit in two ways.

    First, they precisely measured both the activity of individual genes in the circuit throughout the tumble-and-swim cycle. Then they derived a mathematical equation that describes the probability of cells flipping between swim and tumble motions.

    Additional equations describe other aspects of the system, such as the dynamics of the synthesis, diffusion and deactivation of one of the cell-to-cell chemical signal AHL.

    This three-pronged approach of "wet-lab" experiments, precise measurements of the results, and mathematical modeling of the system, characterize the emerging discipline of quantitative biology, Hwa said. "This is a prototype, a model of the kind of biology we want to do."

  • UCSD Physicist Terry Hwa elected to Fellowship in the American Academy of Microbiology
  • Fellows of the Academy are elected annually through a highly selective, peer-review process, based on their records of scientific achievement and original contributions that have advanced microbiology. There are over 2,000 Fellows representing all subspecialties of microbiology, including basic and applied research, teaching, public health, industry, and government service.

    Dr. Hwa's lab is interested in attaining a quantitative, predictive understanding of links between molecular interactions and physiological responses in bacteria, focusing mostly on E. coli. They use a complementary two-pronged approach. In a bottom-up approach, his lab performs quantitative characterization of combinatorial transcriptional control and post-transcriptional controls to construct quantitative models of gene regulation based on molecular properties. In a top-down approach, they characterize phenomenological laws governing bacterial growth, metabolism, and gene expression. The phenomenological laws can be exploited to provide precise quantitative predictions between physiological perturbations and responses; they can also be used to guide the elucidation of molecular signaling mechanisms.

Selected Publications