Engineering Yeast Biosensors for Pathogen Detection

Project Overview

Early and precise detection of pathogenic infection at the point of care is critical for effective drug treatment and disease progression monitoring. Peptide/protein biomarkers are reliable indicators of pathogenic infection, which are typically detected by immunoassays. However, conventional immunoassays usually require expensive reagents, specialized equipment, and well-trained personnel, which may not be available at the point of care. As an alternative, a whole-cell microbial biosensor with engineered synthetic gene circuits to detect biomarkers could serve as an attractive point-of-care biosensor. Yeast is an ideal microbe for this purpose because it has well-developed genetic modification tools and it can provide an inexpensive supply chain as a safe and portable biosensor. Toward building a yeast whole cell biosensor, we developed a baker's yeast equipped with synthetic membrane receptors to respond to a small molecule ligand as a proof-of-concept study. These engineered receptors include three key components: (1) "a single-domain antibody, called nanobody" for extracellular ligand binding, (2) "a yeast membrane two-hybrid system" for signal transducing, and (3) "a protein reporter" for signal reading. Our engineered receptors were localized to the yeast plasma membrane and exhibited a graded dose-response relationship at various ligand concentrations from nanomolar to millimolar (nM to mM), which has a dynamic range appropriate to be used for biomarker detection. We also observed spontaneous activation that needs to be further optimized for increasing receptor sensitivity. This yeast biosensor has the potential to detect various infectious diseases by replacing the nanobody with one targeting a disease-specific biomarker.

Mission Impact

This project demonstrated a novel synthetic biology platform, where engineered yeast cells with a synthetic receptor are capable of sensing a small molecule ligand. This platform has the potential to detect other disease-specific biomarkers as long as a nanobody against the biomarker can be generated. The success of this project marks the first critical step towards a portable biomarker detection device (e.g., dip stick) for early diagnosis of infectious disease at the point of care. In addition, these biosensors have the potential to be also used as an in vivo sensor for gut disease diagnosis, or as a forensic tool. This yeast biosensor provides a novel detection platform that well aligns with Lawrence Livermore National Laboratory's mission to develop biological threat countermeasures, strengthening the bioscience and bioengineering core competency by expanding synthetic biology capabilities, and creating new technologies to respond to national security challenges. We believe that this novel biosensor will significantly contribute to achieving Livermore's mission to develop biological threat countermeasures and new technologies to respond to national security challenges.