(7u) Photoautotrophic Synthesis of Designer Polysaccharides

The synthesis of a variety of complex products can be achieved through microbial bioprocessing. These environmentally-friendly processes can convert renewable resources into the compound of interest without the creation of toxic by-products. Industrial microbiology has relied on organisms, including E. coli and S. cerevisiae, which require the addition of an organic source of reduced carbon, limiting profitability. While the use of autotrophic microbes could address this issue, the ability to forward engineer these potential microbial cell factories is in its infancy. Synthetic biology tools that provide complex and specific control of gene expression are essential for harnessing these organisms’ metabolic potential. I have developed a number of genetic circuits that control transcriptional regulation for the model cyanobacterium, Synechocystis sp. PCC 6803. These single-input and multi-input regulators coordinate industrially-relevant signals, including light, oxygen, and the cell’s nitrogen status, to control gene expression in the photosynthetic, carbon-fixing host. I have started similar work in the purple nonsulfur bacterium Rhodopseudomonas palustris CGA009, a photosynthetic, nitrogen and carbon-fixing bacterium that can also break down aromatic compounds, such as depolymerized lignin, anaerobically.

These synthetic biology tools can now be applied to the production of a number of compounds of interest. One such family of compounds is polysaccharides. Cyanobacteria produce complex polysaccharides, composed of a number of different sugars and non-carbohydrate constituents, which are polymerized and exported to the cell's surface. The cyanobacteria change the composition of these exopolysaccharides (EPS) to help them adapt to a range of environmental conditions. The basics of the EPS enzymatic process are understood, but synthetic control to produce specific functionalities has yet to be achieved. I will utilize my experience developing synthetic biology tools for photoautotrophs to engineer cyanobacteria as novel polysaccharide producing hosts. The potential applications are broad, including water treatment, antivirals, biofilm formation, stress tolerance, phage resistance, and more. The development of a cyanobacterial host for the production of polysaccharides could lead to new and unique compounds that are designed based on the specific need.

Successful Proposals:

Nebraska Corn Board, NSF Graduate Research Fellowship, People, Prosperity and the Planet Student Design Competition for Sustainability

Postdoctoral Project:

"Anaerobic conversion of monolignols into a plastic precursor"

Under the supervision of Dr. Rajib Saha, Department of Chemical and Biomolecular Engineering, University of Nebraska

PhD Dissertation:

“Genetic Circuits for Transcriptional Regulation in Synechocystis sp. PCC 6803”

Under the supervision of Dr. Tae Seok Moon, Department of Energy, Environmental & Chemical Engineering, Washington University in St. Louis

Selected Publications:

CM Immethun and TS Moon. in Synthetic Biology of Cyanobacteria Genetic Engineering of Cyanobacteria (Springer/Nature Press) Invited chapter (in preparation).

CM Immethun, DM DeLorenzo, CM Focht, D Gupta, CB Johnson, TS Moon. Physical, Chemical and Metabolic State Transcriptional Regulators Expand the Synthetic Biology Toolbox for Synechocystis sp. PCC 6803, Biotechnol Bioeng. 114:7 (2017).

N Wan, DM DeLorenzo, L He, L You, CM Immethun, G Wang, EEK Baidoo, W Hollinshead, JD Keasling, TS Moon, YJ Tang. Cyanobacterial Carbon Metabolism: Fluxome Plasticity and Oxygen Dependence, Biotechnol Bioeng. 114:7 (2017).

CM Immethun, KM Ng, DM DeLorenzo, YC Lee, B Waldron-Feinstein, TS Moon. Oxygen-Responsive Genetic Circuits Constructed in Synechocystis sp. PCC 6803, Biotechnol Bioeng. 113:2 (2016).

BM Berla, R Saha, CM Immethun, CD Maranas, TS Moon, HB Pakrasi. Synthetic Biology of Cyanobacteria: Unique Challenges and Opportunities, Front. Microbio. 4:246 (2013).

Teaching Interests:

Knowledge acquired in college covers only a small part of what an engineer will need to know throughout their career. It provides the foundation from which we start solving a problem; yet, the broad, complex and dynamic situations engineers face require the confidence to think creatively and the ability to direct our own learning. Students’ development of a firm knowledge base from which they have the confidence to solve the variety of problems they will face throughout their careers is my first educational objective. My students will tackle realistic problems designed to increase their comfort with resolving underdetermined systems, addressing the complex web of needs and constraints, thinking creatively, and communicating effectively. Practicing an organized and dynamically controlled thought process in new learning situations is the second educational objective for my students. By assessing the task at hand, evaluating the available resources, planning the approach, applying and monitoring the planned strategies, reflecting on the success of the planned strategies, and revising by adjusting the approach, securing additional resources and sometimes even re-assessing the task, students become self-directed learners. My courses utilize goal-directed practice with targeted feedback to help them embrace the learning process and realize its utility in solving the problems they will encounter. I returned to academia propelled by the desire to help students construct the foundation from which they can make important contributions to the challenges we face as a society. My instructional strategies and assessment methods are designed to support that goal and my educational objectives.

Selected Teaching Experience:

Teaching Assistant, Chemical Process Dynamics and Control - Received the EECE Graduate Student Teaching Award, based on student evaluations

Advisor, International Genetically Engineered Machine (iGEM) Competition - Washington University in St. Louis and University of Nebraska teams

Mentor, 11 Graduate Rotation and Undergraduate Students, Washington University in St. Louis - 7 are co-authors on my publications

Judge, International Genetically Engineered Machine (iGEM) Competition's Giant Jamboree

Teacher Workshop Instructor, BioBuilder^® Educational Foundation