Christopher Dundas received his B.S. in Chemical Engineering (’15) with a minor in Biotechnology at the University at Buffalo. He received his Ph.D. in Chemical Engineering (’20) at the University of Texas at Austin, under the guidance of Dr. Benjamin (Keith) Keitz. During his doctoral training, Christopher studied and engineered electroactive soil bacteria – a unique class of microbes that can directly convert carbon sources into electrical energy. Using techniques in materials science and synthetic biology, he demonstrated that bacterial electron transfer can control the formation of a variety of functional organic and inorganic materials. At UT Austin, Christopher also developed genetic tools that increase the programmability and responsiveness of bioelectrical behavior.
At Stanford, Christopher is using bacterial/plant synthetic biology to uncover how plants transfer carbon from roots to soil and aid terrestrial carbon sequestration.
Honors & Awards
TomKat Center Postdoctoral Fellowship in Sustainable Energy, TomKat Center (2021-2023)
NSF Graduate Research Fellowship (Honorable Mention), National Science Foundation (2015)
Barry M. Goldwater Scholarship, Goldwater Foundation (2013-2015)
Postdoctoral Fellow, Stanford University, Biology (2021)
Postdoctoral Fellow, University of Texas at Austin, Chemical Engineering (2020)
Ph.D., University of Texas at Austin, Chemical Engineering (2020)
B.S., University at Buffalo, Chemical Engineering (2015)
Jose Dinneny, Postdoctoral Faculty Sponsor
Current Research and Scholarly Interests
Soil can have an enormous impact on climate change mitigation, as atmospheric CO2 is captured and stored in large quantities by soil organic matter. Plants mediate carbon sequestration by transferring aboveground photosynthesis products to belowground roots. This carbon is stabilized into soil pools by root growth/biomass turnover, exudation of organic compounds, and metabolization by soil microbes. Crops bioengineered to increase soil carbon input could boost net CO2 capture and improve agricultural productivity (e.g., via elevated water and nutrient availability). However, genetic engineering targets that control carbon exchange from roots to soil remain poorly defined. Since carbon distribution within plants is controlled by sugar metabolization and transport, genes that alter these processes may also regulate carbon input to root-proximal soil (i.e., the rhizosphere). At Stanford, Christopher will study how these genes affect soil carbon input by Setaria viridis, a model energy grass that is a promising sustainable fuel source. Leveraging high throughput root imaging technology and genetic circuit design, he will construct root-associating bacterial strains and transgenic Setaria that allow researchers to measure/modulate sugar flux from root systems. These living sensors/actuators will be used to determine genetic design rules of soil carbon input at the root-rhizosphere interface. Results will inform engineering of biofertilizer bacteria and functional plant genes that can increase carbon release into soils by other food- and energy-relevant crops.
Molecular Engineering of Hydrogels for Rapid Water Disinfection and Sustainable Solar Vapor Generation.
Advanced materials (Deerfield Beach, Fla.)
Consumption of unsafe water is a major cause of morbidity and mortality in developing regions. Pasteurizing or boiling water to remove pathogens is energy-intensive and often impractical to off-grid communities. Therefore, low capital cost, rapid and energy-efficient water disinfection methods are urgently required to address global challenges of safe water access. Here, anti-bacterial hydrogels (ABHs) with catechol-enabled molecular-level hydrogen peroxide generators and quinone-anchored activated carbon particles are designed for effective water treatment. The bactericidal effect is attributed to the synergy of hydrogen peroxide and quinone groups to attack essential cell components and disturb bacterial metabolism. ABHs can be directly used as tablets to achieve >99.999% water disinfection efficiency within 60min without energy input. No harmful byproducts are formed during the treatment process, after which the ABH tablets can be easily removed without residues. Taking advantage of their excellent photothermal and biofouling-resistant properties, ABHs can also be applied as solar evaporators to achieve stable water purification under sunlight (≤1kW m-2 ) after months of storage and operation in bacteria-containing river water. The ABH platform offers reduced energy and chemical demands for point-of-use water treatment technologies in remote areas and emergency rescue applications.
View details for DOI 10.1002/adma.202102994
View details for PubMedID 34292641
The role of chemotaxis and efflux pumps on nitrate reduction in the toxic regions of a ciprofloxacin concentration gradient
Spatial concentration gradients of antibiotics are prevalent in the natural environment. Yet, the microbial response in these heterogeneous systems remains poorly understood. We used a microfluidic reactor to create an artificial microscopic ecosystem that generates diffusive gradients of solutes across interconnected microenvironments. With this reactor, we showed that chemotaxis toward a soluble electron acceptor (nitrate) allowed Shewanella oneidensis MR-1 to inhabit and sustain metabolic activity in highly toxic regions of the antibiotic ciprofloxacin (>80× minimum inhibitory concentration, MIC). Acquired antibiotic resistance was not observed for cells extracted from the reactor, so we explored the role of transient adaptive resistance by probing multidrug resistance (MDR) efflux pumps, ancient elements that are important for bacterial physiology and virulence. Accordingly, we constructed an efflux pump deficient mutant (∆mexF) and used resistance-nodulation-division (RND) efflux pump inhibitors (EPIs). While batch results showed the importance of RND efflux pumps for microbial survival, microfluidic studies indicated that these pumps were not necessary for survival in antibiotic gradients. Our work contributes to an emerging body of knowledge deciphering the effects of antibiotic spatial heterogeneity on microorganisms and highlights differences of microbial response in these systems versus well-mixed batch conditions.
View details for DOI 10.1038/s41396-021-00975-1
View details for Web of Science ID 000645491600001
View details for PubMedID 33927341
Tuning Extracellular Electron Transfer by Shewanella oneidensis Using Transcriptional Logic Gates
ACS SYNTHETIC BIOLOGY
2020; 9 (9): 2301-2315
Extracellular electron transfer (EET) pathways, such as those in the bacterium Shewanella oneidensis, interface cellular metabolism with a variety of redox-driven applications. However, designer control over EET flux in S. oneidensis has proven challenging because a functional understanding of its EET pathway proteins and their effect on engineering parametrizations (e.g., response curves, dynamic range) is generally lacking. To address this, we systematically altered transcription and translation of single genes encoding parts of the primary EET pathway of S. oneidensis, CymA/MtrCAB, and examined how expression differences affected model-fitted parameters for Fe(III) reduction kinetics. Using a suite of plasmid-based inducible circuits maintained by appropriate S. oneidensis knockout strains, we pinpointed construct/strain pairings that expressed cymA, mtrA, and mtrC with maximal dynamic range of Fe(III) reduction rate. These optimized EET gene constructs were employed to create Buffer and NOT gate architectures that predictably turn on and turn off EET flux, respectively, in response to isopropyl β-D-1-thiogalactopyranoside (IPTG). Furthermore, we found that response functions generated by these logic gates (i.e., EET activity vs inducer concentration) were comparable to those generated by conventional synthetic biology circuits, where fluorescent reporters are the output. Our results provide insight on programming EET activity with transcriptional logic gates and suggest that previously developed transcriptional circuitry can be adapted to predictably control EET flux.
View details for DOI 10.1021/acssynbio.9b00517
View details for Web of Science ID 000574922400011
View details for PubMedID 32786362
View details for PubMedCentralID PMC7816516
Genetic Control of Radical Cross-linking in a Semisynthetic Hydrogel
ACS BIOMATERIALS SCIENCE & ENGINEERING
2020; 6 (3): 1375-1386
Enhancing materials with the qualities of living systems, including sensing, computation, and adaptation, is an important challenge in designing next-generation technologies. Living materials address this challenge by incorporating live cells as actuating components that control material function. For abiotic materials, this requires new methods that couple genetic and metabolic processes to material properties. Toward this goal, we demonstrate that extracellular electron transfer (EET) from Shewanella oneidensis can be leveraged to control radical cross-linking of a methacrylate-functionalized hyaluronic acid hydrogel. Cross-linking rates and hydrogel mechanics, specifically storage modulus, were dependent on various chemical and biological factors, including S. oneidensis genotype. Bacteria remained viable and metabolically active in the networks for a least 1 week, while cell tracking revealed that EET genes also encode control over hydrogel microstructure. Moreover, construction of an inducible gene circuit allowed transcriptional control of storage modulus and cross-linking rate via the tailored expression of a key electron transfer protein, MtrC. Finally, we quantitatively modeled hydrogel stiffness as a function of steady-state mtrC expression and generalized this result by demonstrating the strong relationship between relative gene expression and material properties. This general mechanism for radical cross-linking provides a foundation for programming the form and function of synthetic materials through genetic control over extracellular electron transfer.
View details for DOI 10.1021/acsbiomaterials.9b01773
View details for Web of Science ID 000519150300007
View details for PubMedID 33313392
View details for PubMedCentralID PMC7725273
Microbial reduction of metal-organic frameworks enables synergistic chromium removal
2019; 10: 5212
Redox interactions between electroactive bacteria and inorganic materials underpin many emerging technologies, but commonly used materials (e.g., metal oxides) suffer from limited tunability and can be challenging to characterize. In contrast, metal-organic frameworks exhibit well-defined structures, large surface areas, and extensive chemical tunability, but their utility as microbial substrates has not been examined. Here, we report that metal-organic frameworks can support the growth of the metal-respiring bacterium Shewanella oneidensis, specifically through the reduction of Fe(III). In a practical application, we show that cultures containing S. oneidensis and reduced metal-organic frameworks can remediate lethal concentrations of Cr(VI) over multiple cycles, and that pollutant removal exceeds the performance of either component in isolation or bio-reduced iron oxides. Our results demonstrate that frameworks can serve as growth substrates and suggest that they may offer an alternative to metal oxides in applications seeking to combine the advantages of bacterial metabolism and synthetic materials.
View details for DOI 10.1038/s41467-019-13219-w
View details for Web of Science ID 000496922700002
View details for PubMedID 31740677
View details for PubMedCentralID PMC6861306
Extracellular Electron Transfer by Shewanella oneidensis Controls Palladium Nanoparticle Phenotype
ACS SYNTHETIC BIOLOGY
2018; 7 (12): 2726-2736
The relative scarcity of well-defined genetic and metabolic linkages to material properties impedes biological production of inorganic materials. The physiology of electroactive bacteria is intimately tied to inorganic transformations, which makes genetically tractable and well-studied electrogens, such as Shewanella oneidensis, attractive hosts for material synthesis. Notably, this species is capable of reducing a variety of transition-metal ions into functional nanoparticles, but exact mechanisms of nanoparticle biosynthesis remain ill-defined. We report two key factors of extracellular electron transfer by S. oneidensis, the outer membrane cytochrome, MtrC, and soluble redox shuttles (flavins), that affect Pd nanoparticle formation. Changes in the expression and availability of these electron transfer components drastically modulated particle synthesis rate and phenotype, including their structure and cellular localization. These relationships may serve as the basis for biologically tailoring Pd nanoparticle catalysts and could potentially be used to direct the biogenesis of other metal nanomaterials.
View details for DOI 10.1021/acssynbio.8b00218
View details for Web of Science ID 000454568100003
View details for PubMedID 30396267
Shewanella oneidensis as a living electrode for controlled radical polymerization
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2018; 115 (18): 4559-4564
Metabolic engineering has facilitated the production of pharmaceuticals, fuels, and soft materials but is generally limited to optimizing well-defined metabolic pathways. We hypothesized that the reaction space available to metabolic engineering could be expanded by coupling extracellular electron transfer to the performance of an exogenous redox-active metal catalyst. Here we demonstrate that the electroactive bacterium Shewanella oneidensis can control the activity of a copper catalyst in atom-transfer radical polymerization (ATRP) via extracellular electron transfer. Using S. oneidensis, we achieved precise control over the molecular weight and polydispersity of a bioorthogonal polymer while similar organisms, such as Escherichia coli, showed no significant activity. We found that catalyst performance was a strong function of bacterial metabolism and specific electron transport proteins, both of which offer potential biological targets for future applications. Overall, our results suggest that manipulating extracellular electron transport pathways may be a general strategy for incorporating organometallic catalysis into the repertoire of metabolically controlled transformations.
View details for DOI 10.1073/pnas.1800869115
View details for Web of Science ID 000431119600035
View details for PubMedID 29666254
View details for PubMedCentralID PMC5939106
Super-resolution imaging of synaptic and Extra-synaptic AMPA receptors with different-sized fluorescent probes
Previous studies tracking AMPA receptor (AMPAR) diffusion at synapses observed a large mobile extrasynaptic AMPAR pool. Using super-resolution microscopy, we examined how fluorophore size and photostability affected AMPAR trafficking outside of, and within, post-synaptic densities (PSDs) from rats. Organic fluorescent dyes (≈4 nm), quantum dots, either small (≈10 nm diameter; sQDs) or big (>20 nm; bQDs), were coupled to AMPARs via different-sized linkers. We find that >90% of AMPARs labeled with fluorescent dyes or sQDs were diffusing in confined nanodomains in PSDs, which were stable for 15 min or longer. Less than 10% of sQD-AMPARs were extrasynaptic and highly mobile. In contrast, 5-10% of bQD-AMPARs were in PSDs and 90-95% were extrasynaptic as previously observed. Contrary to the hypothesis that AMPAR entry is limited by the occupancy of open PSD 'slots', our findings suggest that AMPARs rapidly enter stable 'nanodomains' in PSDs with lifetime >15 min, and do not accumulate in extrasynaptic membranes.
View details for DOI 10.7554/eLife.27744
View details for Web of Science ID 000408632200001
View details for PubMedID 28749340
View details for PubMedCentralID PMC5779237
Expression and purification of soluble monomeric streptavidin in Escherichia coli
APPLIED MICROBIOLOGY AND BIOTECHNOLOGY
2014; 98 (14): 6285-6295
We recently reported the engineering of monomeric streptavidin (mSA) for use in monomeric detection of biotinylated ligands. Although mSA can be expressed functionally on the surface of mammalian cells and yeast, the molecule does not fold correctly when expressed in Escherichia coli. Refolding from inclusion bodies is cumbersome and yields a limited amount of purified protein. Improving the final yield should facilitate its use in biotechnology. We tested the expression and purification of mSA fused to GST, MBP, thioredoxin, and sumo tags to simplify its purification and improve the yield. The fusion proteins can be expressed solubly in E. coli and increase the yield by more than 20-fold. Unmodified mSA can be obtained by proteolytically removing the fusion tag. Purified mSA can be immobilized on a solid matrix to purify biotinylated ligands. Together, expressing mSA as a fusion with a solubilization tag vastly simplifies its preparation and increases its usability in biotechnology.
View details for DOI 10.1007/s00253-014-5682-y
View details for Web of Science ID 000338237400010
View details for PubMedID 24691867
Streptavidin-biotin technology: improvements and innovations in chemical and biological applications
APPLIED MICROBIOLOGY AND BIOTECHNOLOGY
2013; 97 (21): 9343-9353
Streptavidin and its homologs (together referred to as streptavidin) are widely used in molecular science owing to their highly selective and stable interaction with biotin. Other factors also contribute to the popularity of the streptavidin-biotin system, including the stability of the protein and various chemical and enzymatic biotinylation methods available for use with different experimental designs. The technology has enjoyed a renaissance of a sort in recent years, as new streptavidin variants are engineered to complement native proteins and novel methods of introducing selective biotinylation are developed for in vitro and in vivo applications. There have been notable developments in the areas of catalysis, cell biology, and proteomics in addition to continued applications in the more established areas of detection, labeling and drug delivery. This review summarizes recent advances in streptavidin engineering and new applications based on the streptavidin-biotin interaction.
View details for DOI 10.1007/s00253-013-5232-z
View details for Web of Science ID 000325617900005
View details for PubMedID 24057405