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Graduate School of Biomedical Sciences

The Wai-Leung Ng Lab

The Vibrio cholerae Quorum Sensing System

The Ng Lab studies the regulatory pathways that enable human pathogen Vibrio cholerae to thrive in different environments. These signaling systems are composed of transmembrane phosphorelay proteins, RNA regulators, and chemical second messengers that are widely used by bacteria to control many critical cellular functions. Our goal is to define the underlying principles governing these regulatory systems which can be applied to other bacterial signal transduction networks. The overarching goal is to use our findings to develop new strategies for treating and preventing cholera and other infectious diseases.

The causative agent of the disease cholera, Vibrio cholerae, infects the small intestine of humans and causes massive diarrhea. Cholera is a devastating disease, especially in developing countries, and it is currently in the 7th pandemic. Like many bacterial pathogens, V. cholerae depends on an intricate cell-cell communication system, called Quorum Sensing (QS), to precisely regulate the timing of production of colonization factors and toxins inside the host. Furthermore, biofilm formation, genetic exchange, Type VI secretion, and many important processes are controlled by QS in V. cholerae. We discovered that four sensory inputs function in parallel to regulate V. cholerae QS (Figure 1). These parallel signaling systems sense distinct chemical signals to determine the density and complexity of the population. Surprisingly, any one of these communication pathways appears to be sufficient to foster host colonization. We are interested in understanding the molecular mechanisms underpinning signal production and signal detection in these new QS pathways; we also focus on studying the temporal and spatial dynamics of QS gene expression inside the host. Our goal is to fully understand how and why bacteria perceive multiple parallel sensory inputs to precisely control gene expression in different niches.

Ng Fig 1

Figure 1. The Vibro cholerea quorum sensing circuit.

A novel second messenger signaling pathway in V. cholerae

The current pandemic V. cholerae strain belongs to the El Tor biotype and it is characterized by the possession of many pathogenicity islands (PAIs). We discovered that quorum sensing (QS) regulates some genes within one of the PAIs called VSP-I. These genes are essential for production of a novel class of second messenger known as cyclic GMP-AMP (cGAMP). Even though cGAMP has been found in other bacteria and is well studied in eukaryotes as a key regulator of innate immune response, how this cyclic dinucleotide regulates its targets in prokaryotes is unclear. We have identified the first protein target of cGAMP in V. cholerae (Figure 2) and are interested in understanding how cGAMP regulates different cellular processes. We also focus on the mechanisms used by QS and other novel regulatory systems that control cGAMP activity inside V. cholerae cells. We hope to generate a new paradigm instructive for the study of second messenger function and regulation in all living systems.

Ng Fig 2

Figure 2. The Vibrio cholerae cGAMP signaling pathway

Engineered human intestinal tissue model for study of enteric pathogens

The most common models for studying enteric pathogens are in vivo rodent models and in vitro intestinal epithelial cell monolayers. While these models are extremely useful to understand the mechanisms used by different enteric pathogens for infection, they often do not manifest the true outcomes of the diseases that occur in the human intestine. In collaboration with Tufts Bioengineering Department and other members in the Microbiology Department, we are employing a complex bioengineered 3D human intestinal tissue model to determine the host and microbial factors required for early interactions between V. cholerae and human intestinal tissues. These engineered tissues are derived from human small intestinal enteroids and highly mimic the natural host environment encountered by V. cholerae. We aim to fill the unmet need for the development of reliable, physiologically-relevant, 3D in vitro models of the human intestine to fully understand how enteric pathogens attack the human intestine.