Biology subjects

Abel, A. J.

Publications and source records attributed to Abel, A. J..

5 recordsLinked to original sources

bioRxiv2022

Eliminating Genes for a Two Component System Increases PHB Productivity in Cupriavidus basilensis 4G11 Under PHB Suppressing, Non-Stress Conditions

Species of bacteria from the genus Cupriavidus are known, in part, for their ability to produce high amounts of poly-hydroxybutyrate (PHB) making them attractive candidate bioplastic producers. The native production of PHB occurs during periods of metabolic stress, and the process regulating the initiation of PHB accumulation in these organisms is not fully understood. Screening an RB-TnSeq transposon library of Cupriavidus basilensis 4G11 allowed us to identify two genes of an apparent, uncharacterized two component system which, when omitted from the genome, are capable of increased PHB productivity in balanced, non-stress growth conditions. We observe average increases in PHB productivity of 56% and 41% relative to the wildtype parent strain, upon deleting each of two genes individually from the genome. The increased PHB phenotype disappears, however, in nitrogen-free unbalanced growth conditions suggesting the phenotype is specific to fast-growing, replete, non-stress growth. Bioproduction modeling suggests this phenotype could be due to a decreased reliance on metabolic stress induced by nitrogen limitation to initiate PHB production in the mutant strains. Such strains may allow for the use of single stage, continuous bioreactor systems, which are far simpler than PHB bioproduction schemes used previously. Bioproductivity modeling suggests that omitting this regulation in the cells may increase PHB productivity up to 24% relative to the wildtype organism when using single stage continuous systems. This work furthermore expands our understanding of the regulation of PHB accumulation in Cupriavidus, in particular the initiation of this process upon transition into unbalanced growth regimes.

genomics↗

bioRxiv2022

Charting a narrow course for direct electron uptake-facilitated electromicrobial production

Electromicrobial production (EMP) processes based on CO2-fixing microbes that directly accept electrons from a cathode have received significant attention in the past decade. However, fundamental questions about the performance limits and viability of this strategy remain unanswered. Here, we sought to determine what would be necessary for such a system to compete with alternative sustainable production technologies based on H2-mediated EMP and traditional bioprocessing with crop feedstocks. Using global warming potential as the metric for comparison, we show that each EMP process can outperform sugarcane-based sucrose production. Following a stoichiometric and energetic analysis, direct electron uptake-based EMP would need to achieve a current density >48 mA/cm2 to reach parity with the H2- mediated system. Because this is currently only practical with a gas diffusion electrode (GDE) architecture, we developed a physical model of the proposed bio-GDE and used it to determine the conditions that a microbial catalyst would experience in a reactor. Our analysis demonstrates that unavoidable inefficiencies in the reactor (e.g., kinetic overpotentials and Ohmic losses) require additional energy input, increasing the breakeven current density to [~]91 mA/cm2. At this current density, the microbial catalyst would need to withstand a pH >10.4 and a total salinity >18.8%. Because currently-known electroautotrophs are not adapted to such extreme conditions, we discuss potential improvements to reactor design that may alleviate these challenges, and consider the implications these results have on the engineerability and feasibility of direct electron uptake-based EMP.

bioengineering↗

bioRxiv2021

A comparative life cycle analysis of electromicrobial production systems

Electromicrobial production (EMP) processes represent an attractive strategy for the capture and conversion of CO2 into carbon-based products. We describe the development and application of comprehensive reactor, process, and life cycle impact models to analyze three major EMP systems relying on formate, H2, and acetate as intermediate molecules. Our results demonstrate that EMP systems can achieve a smaller carbon footprint than traditional bioprocessing strategies provided the electric grid is composed of >~90% renewable energy sources. For each of the three products we consider (biomass, enzymes, and lactic acid), the H2-mediated Knallgas bacteria system achieves the lowest overall global warming potential, indicating that this EMP strategy may be best-suited for industrial efforts based on current technology. We also identify environmental hotspots and process limitations that are key sites for future engineering and research efforts for each EMP system. Our analysis demonstrates the utility of an integrated bioelectrochemical model/life cycle assessment framework in both analyzing and aiding the ecodesign of electromicrobial processes and should help guide the design of working, scalable, and sustainable systems.

bioengineering↗

bioRxiv2020

Systems-informed genome mining for electroautotrophic microbial production

Microbial electrosynthesis (MES) systems can store renewable energy and CO2 in many-carbon molecules inaccessible to abiotic electrochemistry. Here, we develop a multiphysics model to investigate the fundamental and practical limits of MES enabled by direct electron uptake and we identify organisms in which this biotechnological CO2-fixation strategy can be realized. Systematic model comparisons of microbial respiration and carbon fixation strategies revealed that, under aerobic conditions, the CO2 fixation rate is limited to <6 mol/cm2/hr by O2 mass transport despite efficient electron utilization. In contrast, anaerobic nitrate respiration enables CO2 fixation rates >50 mol/cm2/hr for microbes using the reductive tricarboxylic acid cycle. Phylogenetic analysis, validated by recapitulating experimental demonstrations of electroautotrophy, uncovered multiple probable electroautotrophic organisms and a significant number of genetically tractable strains that require heterologous expression of <5 proteins to gain electroautotrophic function. The model and analysis presented here will guide microbial engineering and reactor design for practical MES systems.

bioengineering↗

bioRxiv2020

Bioelectrochemical engineering analysis of formate-mediated microbial electrosynthesis

Mediated microbial electrosynthesis (MES) represents a promising strategy for the capture and conversion of CO2 into carbon-based products. We describe the development and application of a comprehensive multiphysics model to analyze a formate-mediated MES reactor. The model shows that this system can achieve a biomass productivity of [~]1.7 g L-1 hr-1 but is limited by a competitive trade-off between O2 gas/liquid mass transfer and CO2 transport to the cathode. Synthetic metabolic strategies are evaluated for formatotrophic growth, which can enable an energy efficiency of [~]21%, a 30% improvement over the Calvin cycle. However, carbon utilization efficiency is only [~]10% in the best cases due to a futile CO2 cycle, so gas recycle will be necessary for greater efficiency. Finally, separating electrochemical and microbial processes into separate reactors enables a higher biomass productivity of [~]2.4 g L-1 hr-1. The mediated MES model and analysis presented here can guide process design for conversion of CO2 into renewable chemical feedstocks.

bioengineering↗