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Zymobacter palmae Pyruvate Decarboxylase is Less Effective Than That of Zymomonas mobilis for Ethanol Production in Metabolically Engineered Synechocystis sp. PCC6803

1
Department of Chemical Sciences, School of Natural Sciences and the Bernal Institute, University of Limerick, V94 T9PX Limerick, Ireland
2
School of Engineering, University of Limerick, V94 T9PX Limerick, Ireland
*
Authors to whom correspondence should be addressed.
Microorganisms 2019, 7(11), 494; https://doi.org/10.3390/microorganisms7110494
Received: 2 August 2019 / Revised: 19 October 2019 / Accepted: 25 October 2019 / Published: 27 October 2019
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
To produce bioethanol from model cyanobacteria such as Synechocystis, a two gene cassette consisting of genes encoding pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are required to transform pyruvate first to acetaldehyde and then to ethanol. However the partition of pyruvate to ethanol comes at a cost, a reduction in biomass and pyruvate availability for other metabolic processes. Hence strategies to divert flux to ethanol as a biofuel in Synechocystis are of interest. PDC from Zymobacter palmae (ZpPDC) has been reported to have a lower Km then the Zymomonas mobilis PDC (ZmPDC), which has traditionally been used in metabolic engineering constructs. The Zppdc gene was combined with the native slr1192 alcohol dehydrogenase gene (adhA) in an attempt to increase ethanol production in the photoautotrophic cyanobacterium Synechocystis sp. PCC 6803 over constructs created with the traditional Zmpdc. Native (Zppdc) and codon optimized (ZpOpdc) versions of the ZpPDC were cloned into a construct where pdc expression was controlled via the psbA2 light inducible promoter from Synechocystis sp. PCC 6803. These constructs were transformed into wildtype Synechocystis sp. PCC 6803 for expression and ethanol production. Ethanol levels were then compared with identical constructs containing the Zmpdc. While strains with the Zppdc (UL071) and ZpOpdc (UL072) constructs did produce ethanol, levels were lower compared to a control strain (UL070) expressing the pdc from Zymomonas mobilis. All constructs demonstrated lower biomass productivity illustrating that the flux from pyruvate to ethanol has a major effect on biomass and ultimately overall biofuel productivity. Thus the utilization of a PDC with a lower Km from Zymobacter palmae unusually did not result in enhanced ethanol production in Synechocystis sp. PCC 6803. View Full-Text
Keywords: alcohol dehydrogenase (ADH); biofuels; cyanobacteria; ethanol; pyruvate decarboxylase (PDC); renewable energy; Synechocystis sp. PCC 6803 alcohol dehydrogenase (ADH); biofuels; cyanobacteria; ethanol; pyruvate decarboxylase (PDC); renewable energy; Synechocystis sp. PCC 6803
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MDPI and ACS Style

Quinn, L.; Armshaw, P.; Soulimane, T.; Sheehan, C.; Ryan, M.P.; Pembroke, J.T. Zymobacter palmae Pyruvate Decarboxylase is Less Effective Than That of Zymomonas mobilis for Ethanol Production in Metabolically Engineered Synechocystis sp. PCC6803. Microorganisms 2019, 7, 494.

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