We are interested in bacterial cell growth and division that are fundamental to bacterial life. We employ genetic and imaging techniques to investigate these processes within the cellular environment, and utilize biochemical reconstitution methods and multidisciplinary approaches to uncover the underlying mechanisms. These research directions have implications for both basic science and modern medicine, with the potential to advance the treatment of bacterial infections at the forefront of medical science.

Current Projects

Metabolic regulation of cell growth and division

Cell morphology, which is determined through the processes of growth and division, is regulated by the metabolic state of a cell. We investigate functional coupling between metabolism and cell growth and division. This is likely inherent in cell physiology to increase the environmental fitness especially under nutrient limitation.

Synthesis and remodeling of bacterial surface structures

Our goals are to explore complexity of the peptidoglycan (PG)-synthesizing proteins and surface glycosylation features.

Research Summary

Molecular Mechanism underlying Min Oscillations

MinE-membrane interactions in the E. coli Min system

The Min system in E. coli is a highly coordinated mechanism that ensures cell division site placement at midcell by oscillating between cell poles, thereby generating a MinC gradient that inhibits septum formation at the poles. This process relies on the dynamic interactions of MinD and MinE, which self-organize into mobile structures on the membrane surface, forming significant spatial and temporal patterns. We reported the first evidence of the direct interaction between MinE and the membrane, a discovery advanced our understanding of the underlying mechanism of the Min system (Hsieh et al., 2010). Our work further explored MinE's roles in inducing membrane curvature, driving membrane deformation, and exhibiting amyloid-like properties (Shih et al., 2011; Zheng et al., 2014). To investigate these features, we employed in vitro polymerization assays and artificial membrane systems, including reconstituted liposomes and supported lipid bilayers, characterizing them through a combination of biochemical techniques, electron microscopy, and atomic force microscopy (Chiang et al., 2015). These findings, particularly the discovery of the MinE-membrane interaction, form a cornerstone for unraveling the intricate molecular mechanisms driving the oscillatory behavior of the Min system.

Exploring New Facets of the Min System

Min System Impacts Membrane Proteome and Metabolism

While Min protein oscillations have been extensively studied from both molecular and biophysical perspectives, it remains a mystery whether this continuous, energy-consuming movement impacts other cellular processes beyond division site selection. We addressed this question using a quantitative proteomics approach to identify differences between the membrane proteomes of wild-type and Δmin mutant strains. The results unveiled new insights into the Min system's role in regulating the membrane proteome by influencing reversible protein interactions with the inner membrane, identification of novel interactors of the Min proteins, and a functional connection between metabolism and the Min system. (Lee et al., 2016)

Min Protein-Mediated Transport and Spatial Separation of Membrane Components

Using biochemical reconstruction methods, we discovered that the ability of Min proteins to dynamically self-organize at membrane surfaces can facilitate the transport of lipids and lipid-anchored proteins and lead to an asymmetric distribution of these biomolecules within the membrane. This phenomenon is governed by steric pressure and component diffusivity in the membrane. This research suggests the function of the Min system in spatially segregating membrane components, extending the function of the Min system beyond cell division. (Shih et al., 2019).

Plasticity of the MinD Concentration gradient in living cells

This study uncovers the dynamic nature of the MinD protein gradients, driven by the interplay between molecular interactions and diffusion within the cell. Live-cell imaging revealed that as cells elongate, the gradient steepens, midcell concentration decreases, and the oscillation period remains relatively stable. Using a mathematical model, we further explored the kinetic rate constants governing these molecular interactions, successfully recapitulated the experimental observations, and uncovered a dynamic equilibrium among these constants that shapes the variable concentration gradients in growing cells. This research enhances the quantitative understanding of Min oscillations in bacterial cell division and emphasizes the relevance of concentration gradients in fundamental biological processes. (Parada et al., 2025)

Cell Wall Synthesis in Bacterial Physiology

Innovative Imaging of Peptidoglycan Metabolism

This work demonstrates the significance of developing peptidoglycan (PG) imaging probes to enhance our understanding of PG metabolism and the action of antibiotics targeting bacterial cell walls. We introduced a new probe involving the fluorescent antibiotics monomycin A (MoeA) to label transglycosylases (TGases). The MoeA probe labels the enzymes responsible for the transglycosylation steps, standing out from the frequently used fluorescent probes for the metabolic labeling of peptidoglycan itself. The MoeA probe allowed us to observe bacterial growth and division cycles through time-lapse imaging and to investigate cell wall growth in methicillin-resistant Staphylococcus aureus (MRSA) strains carrying mecA, especially when conventional β-lactam-based probes were not suitable. (Hsieh et al., 2021)

Unlocking the FtsB-FtsL-FtsQ Complex

This study reveals the first full-length structure of the FtsBLQ complex, a core component of the divisome responsible for the synthesis of septal PG during bacterial cell division. We also demonstrate the functional significance of interface residues within the FtsBLQ complex in cell division by genetics and cell imaging methods. A model for the regulation of PG synthesis by FtsBLQ is proposed, showing that allosteric changes occurring within the FtsBLQ complex can further influence its interactions with other divisome proteins, thereby modulating the synthesis of septal PG. (Nguyen et al., 2023)

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