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Baum C, Zeldes B, Poehlein A, Daniel R, Müller V, Basen M. The energy-converting hydrogenase Ech2 is important for the growth of the thermophilic acetogen Thermoanaerobacter kivui on ferredoxin-dependent substrates. Microbiol Spectr 2024; 12:e0338023. [PMID: 38385688 PMCID: PMC10986591 DOI: 10.1128/spectrum.03380-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Accepted: 01/31/2024] [Indexed: 02/23/2024] Open
Abstract
Thermoanaerobacter kivui is the thermophilic acetogenic bacterium with the highest temperature optimum (66°C) and with high growth rates on hydrogen (H2) plus carbon dioxide (CO2). The bioenergetic model suggests that its redox and energy metabolism depends on energy-converting hydrogenases (Ech). Its genome encodes two Echs, Ech1 and Ech2, as sole coupling sites for energy conservation during growth on H2 + CO2. During growth on other substrates, its redox activity, the (proton-gradient-coupled) oxidation of H2 may be essential to provide reduced ferredoxin (Fd) to the cell. While Ech activity has been demonstrated biochemically, the physiological function of both Ech's is unclear. Toward that, we deleted the complete gene cluster encoding Ech2. Surprisingly, the ech2 mutant grew as fast as the wild type on sugar substrates and H2 + CO2. Hence, Ech1 may be the essential enzyme for energy conservation, and either Ech1 or another enzyme may substitute for H2-dependent Fd reduction during growth on sugar substrates, putatively the H2-dependent CO2 reductase (HDCR). Growth on pyruvate and CO, substrates that are oxidized by Fd-dependent enzymes, was significantly impaired, but to a different extent. While ∆ech2 grew well on pyruvate after four transfers, ∆ech2 did not adapt to CO. Cell suspensions of ∆ech2 converted pyruvate to acetate, but no acetate was produced from CO. We analyzed the genome of five T. kivui strains adapted to CO. Strikingly, all strains carried mutations in the hycB3 subunit of HDCR. These mutations are obviously essential for the growth on CO but may inhibit its ability to utilize Fd as substrate. IMPORTANCE Acetogens thrive by converting H2+CO2 to acetate. Under environmental conditions, this allows for only very little energy to be conserved (∆G'<-20 kJ mol-1). CO2 serves as a terminal electron acceptor in the ancient Wood-Ljungdahl pathway (WLP). Since the WLP is ATP neutral, energy conservation during growth on H2 + CO2 is dependent on the redox metabolism. Two types of acetogens can be distinguished, Rnf- and Ech-type. The function of both membrane-bound enzyme complexes is twofold-energy conversion and redox balancing. Ech couples the Fd-dependent reduction of protons to H2 to the formation of a proton gradient in the thermophilic bacterium Thermoanaerobacter kivui. This bacterium may be utilized in gas fermentation at high temperatures, due to very high conversion rates and the availability of genetic tools. The physiological function of an Ech hydrogenase in T. kivui was studied to contribute an understanding of its energy and redox metabolism, a prerequisite for future industrial applications.
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Affiliation(s)
- Christoph Baum
- Microbiology, Institute for Biological Sciences, University of Rostock, Rostock, Germany
| | - Benjamin Zeldes
- Microbiology, Institute for Biological Sciences, University of Rostock, Rostock, Germany
| | - Anja Poehlein
- Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Georg-August University, Göttingen, Germany
| | - Rolf Daniel
- Genomic and Applied Microbiology & Göttingen Genomics Laboratory, Georg-August University, Göttingen, Germany
| | - Volker Müller
- Department of Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
| | - Mirko Basen
- Microbiology, Institute for Biological Sciences, University of Rostock, Rostock, Germany
- Department of Maritime Systems, Interdisciplinary Faculty, University of Rostock, Rostock, Germany
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Lai B, Bernhardt PV, Krömer JO. Cytochrome c Reductase is a Key Enzyme Involved in the Extracellular Electron Transfer Pathway towards Transition Metal Complexes in Pseudomonas Putida. CHEMSUSCHEM 2020; 13:5308-5317. [PMID: 32678505 PMCID: PMC7589348 DOI: 10.1002/cssc.202001645] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/16/2020] [Indexed: 05/06/2023]
Abstract
Mediator-based extracellular electron transfer (EET) pathways can balance the redox metabolism of microbes. However, such electro-biosynthesis processes are constrained by the unknown underlying EET mechanisms. In this paper, Pseudomonas putida was studied to systematically investigate its EET pathway to transition metal complexes (i. e., [Fe(CN)6 ]3-/4- and [Co(bpy)3 ]3+/2+ ; bpy=2,2'-bipyridyl) under anaerobic conditions. Comparative proteomics showed the aerobic respiratory components were upregulated in a bioelectrochemical system without oxygen, suggesting their potential contribution to EET. Further tests found inhibiting cytochrome c oxidase activity by NaN3 and NADH dehydrogenase by rotenone did not significantly change the current output. However, the EET pathway was completely blocked, while cytochrome c reductase activity was inhibited by antimycin A. Although it cannot be excluded that cytochrome c and the periplasmic subunit of cytochrome c oxidase donate electrons to the transition metal complexes, these results strongly demonstrate that cytochrome c reductase is a key complex for the EET pathway.
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Affiliation(s)
- Bin Lai
- Systems Biotechnology group, Department of Solar MaterialsHelmholtz Centre for Environmental Research - UFZLeipzig04318Germany
- Advanced Water Management CentreThe University of QueenslandBrisbane4072Australia
| | - Paul V. Bernhardt
- School of Chemical and Molecular BiosciencesThe University of QueenslandBrisbane4072Australia
| | - Jens O. Krömer
- Systems Biotechnology group, Department of Solar MaterialsHelmholtz Centre for Environmental Research - UFZLeipzig04318Germany
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Nies SC, Alter TB, Nölting S, Thiery S, Phan ANT, Drummen N, Keasling JD, Blank LM, Ebert BE. High titer methyl ketone production with tailored Pseudomonas taiwanensis VLB120. Metab Eng 2020; 62:84-94. [PMID: 32810591 DOI: 10.1016/j.ymben.2020.08.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/13/2020] [Accepted: 08/05/2020] [Indexed: 12/12/2022]
Abstract
Methyl ketones present a group of highly reduced platform chemicals industrially produced from petroleum-derived hydrocarbons. They find applications in the fragrance, flavor, pharmacological, and agrochemical industries, and are further discussed as biodiesel blends. In recent years, intense research has been carried out to achieve sustainable production of these molecules by re-arranging the fatty acid metabolism of various microbes. One challenge in the development of a highly productive microbe is the high demand for reducing power. Here, we engineered Pseudomonas taiwanensis VLB120 for methyl ketone production as this microbe has been shown to sustain exceptionally high NAD(P)H regeneration rates. The implementation of published strategies resulted in 2.1 g Laq-1 methyl ketones in fed-batch fermentation. We further increased the production by eliminating competing reactions suggested by metabolic analyses. These efforts resulted in the production of 9.8 g Laq-1 methyl ketones (corresponding to 69.3 g Lorg-1 in the in situ extraction phase) at 53% of the maximum theoretical yield. This represents a 4-fold improvement in product titer compared to the initial production strain and the highest titer of recombinantly produced methyl ketones reported to date. Accordingly, this study underlines the high potential of P. taiwanensis VLB120 to produce methyl ketones and emphasizes model-driven metabolic engineering to rationalize and accelerate strain optimization efforts.
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Affiliation(s)
- Salome C Nies
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Tobias B Alter
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Sophia Nölting
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Susanne Thiery
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - An N T Phan
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Noud Drummen
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Jay D Keasling
- Joint BioEnergy Institute, Emeryville, CA, 94608, USA; Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800, Lyngby, Denmark; Lawrence Berkeley National Laboratory, Biological Systems and Engineering Division, Berkeley, CA, 94720, USA; Virtual Institute of Microbial Stress and Survival, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA; Dept. of Bioengineering, University of California, Berkeley, CA, 94720, USA; Dept. of Chemical Engineering, University of California, Berkeley, CA, 94720, USA; Synthetic Biochemistry Center, Institute for Synthetic Biology, Shenzhen Institutes for Advanced Technologies, Shenzhen, China
| | - Lars M Blank
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany
| | - Birgitta E Ebert
- iAMB-Institute of Applied Microbiology, ABBt-Aachen Biology and Biotechnology, RWTH Aachen University, DE, Germany; Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland, Brisbane, QLD, 4072, Australia; CSIRO Future Science Platform in Synthetic Biology, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Black Mountain, ACT, 2601, Australia.
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