Synthetic biology of metabolic cycles for Enhanced CO capture and Sequestration.

In most organisms, the tri-carboxylic acid cycle (TCA cycle) is an essential metabolic system that is involved in both energy generation and carbon metabolism. Its uni-directionality, however, restricts its use in synthetic biology and carbon fixation. Here, it is describing the use of the modified TCA cycle, called the Tri-carboxylic acid Hooked to Ethylene by Enzyme Reactions and Amino acid Synthesis, the reductive tricarboxylic acid branch/4-hydroxybutyryl-CoA/ethylmalonyl-CoA/acetyl-CoA (THETA) cycle, in Escherichia coli for the purposes of carbon fixation and amino acid synthesis. Three modules make up the THETA cycle: (1) pyruvate to succinate transformation, (2) succinate to crotonyl-CoA change, and (3) crotonyl-CoA to acetyl-CoA and pyruvate change. It is presenting each module's viability in vivo and showing how it integrates into the E. coli metabolic network to support growth on minimal medium without the need for outside supplementation. Enzyme optimization, route redesign, and heterologous expression were used to get over metabolic roadblocks and produce functional modules. Furthermore, the THETA cycle may be improved by including components of the Carbon-Efficient Tri-Carboxylic Acid Cycle (CETCH cycle) to improve carbon fixation. THETA cycle's promise as a platform for applications in synthetic biology and carbon fixation.