Astroplastic: A start-to-finish process for polyhydroxybutyrate production from solid human waste using genetically engineered bacteria to address the challenges for future manned Mars missions

Abstract

Space exploration has long been a source of inspiration, challenging scientists and engineers to find innovative solutions to various problems. One of the current focuses in space exploration is to send humans to Mars. However, the challenge of transporting materials to Mars and the need for waste management processes are two major obstacles for these long-duration missions.\n\nTo address these two challenges a process called Astroplastic was developed that produces polyhydroxybutyrate (PHB) from solid human waste, which can be used to 3D print useful items for astronauts. PHB granules are naturally produced by bacteria such as Ralstonia eutropha and Pseudomonas aeruginosa for carbon and energy storage. The phaJ, phaC, and phaCBA genes were cloned from these native PHB-producing bacteria into Escherichia coli. These genes code for enzymes that aid in PHB production by converting products of glycolysis and {beta}-oxidation pathways, such as acetyl-CoA and enoyl-CoA, into PHB. To ensure a continuous PHB production system and to eliminate the need for cell lysis to extract PHB, recombinant E. coli was engineered to use the genes in its natural type I secretion system to secrete PHB. The C-terminal of the HlyA secretion tag was fused to phasin (PhaP), a protein originally from R. eutropha. Phasin-HlyA electrostatically binds PHB granules and transports them outside of the cell.\n\nIn addition to genetically engineering bacteria, a concept for start-to-finish PHB production process was designed. Integrating expert feedback and experimental results, conditions for each step of the process including the collection and storage of waste, volatile fatty acid (VFA) fermentation, VFA extraction, PHB fermentation, and PHB extraction were optimized. The optimized system will provide a sustainable and continuous PHB production system, which will address the problems of transportation costs and waste management for future space missions.\n\nFinancial DisclosureMindfuel Science Alberta Foundation Genome Alberta GenScript Polyferm Canada GeekStarter Alberta Integrated DNA Technologies University of Calgary University of Calgary Cumming School of Medicine University of Calgary Bachelor of Sciences University of Calgary Schulich School of Engineering University of Calgary OBrien Centre for the Bachelor of Health Sciences City of Calgary Alberta Innovates The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.\n\nCompeting InterestsThe authors have declared that no competing interests exist.\n\nEthics StatementN/A\n\nData AvailabilityAll data are freely available without restriction.