Shota Atsumi

Engineered cyanobacteria offer a sustainable platform for the conversion of light and CO2 into value-added chemicals. Unlike heterotrophic systems, cyanobacteria do not require organic carbon sources such as glycerol, glucose, or sucrose. In this study, we engineered Synechococcus elongatus PCC 7942 (hereafter 7942) for the production of 1,4-butanediol (14BDO), a precursor used in the synthesis of pharmaceuticals, biodegradable polymers, and resins, directly from CO2. To identify a suitable biosynthetic route, we evaluated three heterologous 14BDO pathways previously developed in heterotrophic hosts. Among these, the carboxylic acid reductase (Car) pathway supported 14BDO production directly from CO2 without supplementation of an exogenous carbon source, whereas the Weimberg pathway required d-xylose supplementation and the CoA-dependent pathway did not produce detectable 14BDO. We therefore focused on the Car pathway and improved production by rewiring carbon flux through the incomplete tricarboxylic acid pathway, directing intermediates toward 2-ketoglutarate as a key metabolic node. Further engineering, including additional expression of ppc and gltA and deletion of glgC, increased 14BDO production, consistent with enhanced carbon availability for 14BDO biosynthesis. This work establishes a functional route for photoautotrophic 14BDO production from CO2 and demonstrates the importance of carbon flux engineering for improving production of non-native chemicals in cyanobacteria.

Engineered living materials (ELMs) integrate synthetic polymers with engineered cells to create systems that sense, respond, and adapt to their environment. While promising as sustainable alternatives to traditional materials, ELMs remain underexplored for use with photoautotrophic organisms. In this study, we evaluate the viability of the cyanobacterium Synechococcus elongatus PCC 7942, which converts carbon dioxide into valuable chemicals using light energy, in three hydrogel matrices previously shown to support heterotrophic cells. S. elongatus remained viable and metabolically active only in a hydrogel formed from bovine serum albumin-conjugated acrylates. When engineered to produce 2,3-butanediol (23BDO), encapsulated cells generated 719 mg L^-1 over four days. Incorporating cells increased the compressive modulus of the material, while accumulated 23BDO reduced it, indicating that bioproduction influences mechanical properties. Fluorescence imaging confirmed high viability and physical immobilization. These results establish that cyanobacteria-based ELMs can enable autotrophic chemical production while modulating material mechanics for sustainable applications.

D-Tagatose, a rare low-calorie sweetener, is ideal for beverages due to its high solubility and low viscosity. Current enzymatic production methods from d-galactose or d-galactitol are limited by reaction reversibility, affecting the yield and purity. This study demonstrates that Escherichia coli harbors a thermodynamically favorable pathway for producing d-tagatose from d-glucose via phosphorylation-epimerization-dephosphorylation steps. GatZ and KbaZ, annotated as aldolase chaperones, exhibit C4 epimerization activity, converting d-fructose-6-phosphate to d-tagatose-6-phosphate. Structural analysis reveals active site differences between these enzymes and class II aldolases, indicating functional divergence. By exploiting the strains' inability to metabolize d-tagatose, carbon starvation was applied to remove sugar byproducts. The engineered strains converted 45 g L^-1 d-glucose to d-tagatose, achieving a titer of 7.3 g L^-1 and a productivity of 0.1 g L^-1 h^-1 under test tube conditions. This approach highlights E. coli as a promising host for efficient d-tagatose production.