Seminar: Microfluidic Bacterial Phenotyping and Genetic Transformation Using Electric Fields

Abstract

The bacterial cell envelope is critical for understanding important physiological behaviors, such as extracellular electron transfer (EET) and antibiotic uptake. Through EET, microbes can transport electrons from their interior to external insoluble electron acceptors (e.g. metal oxides or electrodes in an electrochemical cell), which has attracted tremendous attention due to potential applications in environmental remediation and energy conversion. Another interesting property of the bacterial envelope is the presence of lipopolysaccharide (LPS), one of the major virulence factors in the outer membrane of Gram-negative bacteria. Disrupting LPS assembly is known to sensitize bacteria to antibiotics, thus the presence of LPS is an important phenotype. However, rapid and noninvasive phenotyping of the bacterial cell envelope is challenging. In this talk, we will present how bacterial envelope phenotypes, such as EET and LPS biosynthesis, can be quantified by cell surface polarizability, a dielectric property that can be measured using microfluidic dielectrophoresis. Dielectrophoretic phenotyping is achieved with small cell culture volumes (~100 mL) in a short amount of time (1~2 min per strain). Buie and team show for the first time a strong correlation between bacterial EET and surface polarizability, and verify the broad applicability of this technique using multiple natural and engineered species of bacteria, including wild type strains and cytochrome-deletion mutants of two model EET microbes, Geobacter sulfurreducens and Shewanella oneidensis, and Escherichia coli strains heterologously expressing S. oneidensis EET pathways. Their work demonstrates that cell polarizability is diminished in response to impaired EET pathways (e.g. genetic deletions of outer-membrane cytochromes) and enhanced due to additions of EET components. The team also reports that DEP-based screening is sensitive enough to distinguish E. coli mutants with varying LPS composition. For example, the team demonstrates that E. coli with truncated LPS structure displays decreased surface polarizability. Lastly, the presentation will discuss recent work in the team's laboratory that uses very high electric fields (~10 kV/cm) in microfluidic devices to enable high throughput delivery of nucleic acids to bacterial populations. Results of this work hold exciting promise for rapid screening of bacterial envelope phenotypes and for accelerating genetic engineering of bacteria for industrial applications.

About the speaker

Cullen Buie is an associate professor in MIT’s Department of Mechanical Engineering and director of the Laboratory for Energy and Microsystems Innovation. His laboratory explores flow physics at the microscale for applications in materials science and applied biosciences. His research is applicable to a diverse range of problems, from anti-biofouling surfaces and biofuels to energy storage and bacterial infections.

In 2017 Kytopen, a start-up Buie co-founded that offers a method of genetic engineering 10,000 times faster than current methods, was among the first start-ups to be backed by The Engine, a venture launched by MIT. Buie was honored with the NSF Career Award in 2012, the DuPont Young Professor Award in 2013, the DARPA Young Faculty Award in 2013, and the NSF Presidential Early Career Awards for Scientists and Engineers in 2016.

Buie received his BS from The Ohio State University. He earned his MS and PhD in mechanical engineering at Stanford University and served as a postdoctoral fellow for one year at the University of California-Berkeley.

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