Anaerobic butanol production driven by oxygen-evolving photosynthesis using the heterocyst-forming multicellular cyanobacterium Anabaena sp. PCC 7120
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Cyanobacteria are oxygen-evolving photosynthetic bacteria. Established genetic manipulation methods and recently developed gene-regulation tools have enabled the photosynthetic conversion of carbon dioxide to biofuels and valuable chemicals in cyanobacteria, especially in unicellular cyanobacteria. However, the oxygen sensitivity of enzyme(s) introduced into cyanobacteria hampers productivity in some cases. Anabaena sp. PCC 7120 is a filamentous cyanobacterium consisting of a few hundred of vegetative cells, which perform oxygenic photosynthesis. Upon nitrogen deprivation, heterocysts, which are specialized cells for nitrogen fixation, are differentiated from vegetative cells at semiregular intervals. The micro-oxic environment within heterocysts protects oxygen-labile nitrogenase from oxygen. This study aimed to repurpose the heterocyst as a host for the production of chemicals with oxygen-sensitive enzymes under photosynthetic conditions. Herein, Anabaena strains expressing enzymes of 1-butanol synthetic pathway from the anaerobe Clostridium acetobutylicum within heterocysts were created. A strain that expressed a highly oxygen-sensitive Bcd/EtfAB complex produced 1-butanol even under photosynthetic conditions. Furthermore, the 1-butanol production per heterocyst cell of a butanol-producing Anabaena strain was fivefold higher than that per cell of unicellular cyanobacterium with the same set of 1-butanol synthetic pathway genes. Thus, our study showed the usefulness of Anabaena heterocysts as a chassis for anaerobic production driven by oxygen-evolving photosynthesis.
KeywordsAnaerobic fermentation Butanol production Cyanobacteria Heterocyst Metabolic engineering Oxygen-sensitive enzymes
This work was supported in part by the Institute for Fermentation, Osaka, Japan, and by a Grant-In-Aid for Scientific Research (C) 18K05395 from the Japan Society for the Promotion of Science. We thank NITE Biological Resource Center (NITE, Kisarazu, Japan) and Dr. Tomohisa Kuzuyama (The University of Tokyo, Japan) for kindly providing Clostridium acetobutylicum NBRC 13948 (ATCC 824) genomic DNA and an nphT7 vector, respectively.
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Conflict of interest
The authors declare that they have no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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