초록
<P><B>Background</B></P><P>Cyanobacteria are emerging as green cell factories for sustainable biofuel and chemical production, due to their photosynthetic ability to use solar energy, carbon dioxide and water in a direct process. The model cyanobacterial strain <I>Synechocystis</I> sp. PCC 6803 has been engineered for the isobutanol and 3-methyl-1-butanol production by introducing a synthetic 2-keto acid pathway. However, the achieved productions still remained low. In the present study, diverse metabolic engineering strategies were implemented in <I>Synechocystis</I> sp. PCC 6803 for further enhanced photosynthetic isobutanol and 3-methyl-1-butanol production.</P><P><B>Results</B></P><P>Long-term cultivation was performed on two selected strains resulting in maximum cumulative isobutanol and 3-methyl-1-butanol titers of 1247 mg L<SUP>−1</SUP> and 389 mg L<SUP>−1</SUP>, on day 58 and day 48, respectively. Novel <I>Synechocystis</I> strain integrated with a native 2-keto acid pathway was generated and showed a production of 98 mg isobutanol L<SUP>−1</SUP> in short-term screening experiments. Enhanced isobutanol and 3-methyl-1-butanol production was observed when increasing the <I>kivd</I><SUP><I>S286T</I></SUP> copy number from three to four. Isobutanol and 3-methyl-1-butanol production was effectively improved when overexpressing selected genes of the central carbon metabolism. Identified genes are potential metabolic engineering targets to further enhance productivity of pyruvate-derived bioproducts in cyanobacteria.</P><P><B>Conclusions</B></P><P>Enhanced isobutanol and 3-methyl-1-butanol production was successfully achieved in <I>Synechocystis</I> sp. PCC 6803 strains through diverse metabolic engineering strategies. The maximum cumulative isobutanol and 3-methyl-1-butanol titers, 1247 mg L<SUP>−1</SUP> and 389 mg L<SUP>−1</SUP>, respectively, represent the current highest value reported. The significantly enhanced isobutanol and 3-methyl-1-butanol production in this study further pave the way for an industrial application of photosynthetic cyanobacteria-based biofuel and chemical synthesis from CO<SUB>2</SUB>.</P><P><B>Supplementary Information</B></P><P>The online version contains supplementary material available at 10.1186/s13068-023-02385-1.</P>