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Insulation of a synthetic hydrogen metabolism circuit in bacteria.

ABSTRACT: BACKGROUND:The engineering of metabolism holds tremendous promise for the production of desirable metabolites, particularly alternative fuels and other highly reduced molecules. Engineering approaches must redirect the transfer of chemical reducing equivalents, preventing these electrons from being lost to general cellular metabolism. This is especially the case for high energy electrons stored in iron-sulfur clusters within proteins, which are readily transferred when two such clusters are brought in close proximity. Iron sulfur proteins therefore require mechanisms to ensure interaction between proper partners, analogous to many signal transduction proteins. While there has been progress in the isolation of engineered metabolic pathways in recent years, the design of insulated electron metabolism circuits in vivo has not been pursued. RESULTS:Here we show that a synthetic hydrogen-producing electron transfer circuit in Escherichia coli can be insulated from existing cellular metabolism via multiple approaches, in many cases improving the function of the pathway. Our circuit is composed of heterologously expressed [Fe-Fe]-hydrogenase, ferredoxin, and pyruvate-ferredoxin oxidoreductase (PFOR), allowing the production of hydrogen gas to be coupled to the breakdown of glucose. We show that this synthetic pathway can be insulated through the deletion of competing reactions, rational engineering of protein interaction surfaces, direct protein fusion of interacting partners, and co-localization of pathway components on heterologous protein scaffolds. CONCLUSIONS:Through the construction and characterization of a synthetic metabolic circuit in vivo, we demonstrate a novel system that allows for predictable engineering of an insulated electron transfer pathway. The development of this system demonstrates working principles for the optimization of engineered pathways for alternative energy production, as well as for understanding how electron transfer between proteins is controlled.

SUBMITTER: Agapakis CM

PROVIDER: S-EPMC2847965 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Insulation of a synthetic hydrogen metabolism circuit in bacteria.

Agapakis Christina M CM Ducat Daniel C DC Boyle Patrick M PM Wintermute Edwin H EH Way Jeffrey C JC Silver Pamela A PA

Journal of biological engineering 20100225

<h4>Background</h4>The engineering of metabolism holds tremendous promise for the production of desirable metabolites, particularly alternative fuels and other highly reduced molecules. Engineering approaches must redirect the transfer of chemical reducing equivalents, preventing these electrons from being lost to general cellular metabolism. This is especially the case for high energy electrons stored in iron-sulfur clusters within proteins, which are readily transferred when two such clusters ...[more]

PMID: 20184755

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Project description:Obesity is becoming increasingly widespread in developed countries, and is often associated with heart diseases and diabetes. Elevated levels of plasma free fatty acids are a biochemical hallmark of obesity. Unlike plants and bacteria, mammals cannot utilize fatty acids to generate glucose because of the lack of glyoxylate shunt enzymes. Instead, fatty acids are used for energy storage, and their utilization is regulated at multiple levels ranging from hormonal to metabolic ensuring that glucose is preferentially oxidized before fatty acids. Here we designed a synthetic gene-metabolic circuit to alter the intracellular signaling and metabolic pathways that control fatty acid metabolism. By introducing the Escherichia coli glyoxylate shunt enzymes, isocitrate lyase (AceA) and malate synthase (AceB), into the mitochondria of human hepatocytes, we demonstrated that fatty acid utilization is preferentially increased while glucose uptake is significantly reduced. This bacterial pathway diverts signal metabolites (citrate, acetyl-CoA, and malonyl-CoA) that inhibits fatty acid uptake and provides an additional channel for fatty acid utilization. Remarkably, the hepatocytes readily adapted to the synthetic circuit by a series of global transcriptional and post-translational changes in metabolic and signal transduction pathways that further advanced our design objective. This systems approach illustrates the logic of the synergistic interaction between metabolism and signal transduction. The ready acceptance of this non-native pathway by hepatocytes suggests the plasticity of liver metabolism and opens a possibility for the synthetic approach in regulating human metabolism. Experiment Overall Design: Wild type (WT) human hepatocyte HepG2 and HepG2 cells stably transfected with pBudaceAB (designated ACE), a vector containing isocitrate lyase and malate synthase from E. coli, were analyzed after 24hour exposure to palmitate. Cells were seeded at 70% confluency in 10cm plates with DMEM growth media augmented with 300uM palmitate. After 24hours, total RNA was harvested and hybrized to Affymetrix HG_U133A 2.0 GeneChips. Data was processed using GCOS 1.2 software. Experiment Overall Design: 2 WT biological replicates and 2 ACE biological replicates were analyzed. Experiment Overall Design:

Project description:BackgroundBiofilms in sulfide-rich springs present intricate microbial communities that play pivotal roles in biogeochemical cycling. We studied chemoautotrophically based biofilms that host diverse CPR bacteria and grow in sulfide-rich springs to investigate microbial controls on biogeochemical cycling.ResultsSulfide springs biofilms were investigated using bulk geochemical analysis, genome-resolved metagenomics, and scanning transmission X-ray microscopy (STXM) at room temperature and 87 K. Chemolithotrophic sulfur-oxidizing bacteria, including Thiothrix and Beggiatoa, dominate the biofilms, which also contain CPR Gracilibacteria, Absconditabacteria, Saccharibacteria, Peregrinibacteria, Berkelbacteria, Microgenomates, and Parcubacteria. STXM imaging revealed ultra-small cells near the surfaces of filamentous bacteria that may be CPR bacterial episymbionts. STXM and NEXAFS spectroscopy at carbon K and sulfur L2,3 edges show that filamentous bacteria contain protein-encapsulated spherical elemental sulfur granules, indicating that they are sulfur oxidizers, likely Thiothrix. Berkelbacteria and Moranbacteria in the same biofilm sample are predicted to have a novel electron bifurcating group 3b [NiFe]-hydrogenase, putatively a sulfhydrogenase, potentially linked to sulfur metabolism via redox cofactors. This complex could potentially contribute to symbioses, for example, with sulfur-oxidizing bacteria such as Thiothrix that is based on cryptic sulfur cycling. One Doudnabacteria genome encodes adjacent sulfur dioxygenase and rhodanese genes that may convert thiosulfate to sulfite. We find similar conserved genomic architecture associated with CPR bacteria from other sulfur-rich subsurface ecosystems.ConclusionsOur combined metagenomic, geochemical, spectromicroscopic, and structural bioinformatics analyses of biofilms growing in sulfide-rich springs revealed consortia that contain CPR bacteria and sulfur-oxidizing Proteobacteria, including Thiothrix, and bacteria from a new family within Beggiatoales. We infer roles for CPR bacteria in sulfur and hydrogen cycling. Video Abstract.

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Insulation of a synthetic hydrogen metabolism circuit in bacteria.

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Insulation of a synthetic hydrogen metabolism circuit in bacteria.

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