Photoautotrophic synthesis of butyrate by metabolically engineered cyanobacteria

Direct conversion of carbon dioxide into chemicals using engineered autotrophic microorganisms offers a potential solution for both sustainability and carbon mitigation. Butyrate is an important chemical used in various industries, including fragrance, food, and plastics. A model cyanobacterium Synechococcus elongatus PCC 7942 was engineered for the direct photosynthetic conversion of CO ₂ to butyrate. An engineered Clostridium Coenzyme A (CoA)-dependent pathway leading to the synthesis of butyryl-CoA, the precursor to butyrate, was introduced into S. elongatus PCC 7942. Two CoA removal strategies were then individually coupled to the modified CoA-dependent pathway to yield butyrate production. Similar results were observed between the two CoA removal strategies. The best butyrate producing strain of S. elongatus resulted in an observed butyrate titer of 750 mg/L and a cumulative titer of 1.1 g/L. These results demonstrated the feasibility of photosynthetic butyrate production and expanded the chemical repertoire accessible for production by photoautotrophs.     

Passive skeletal muscle can function as an osmotic engine

Muscles are composite structures. The protein filaments responsible for force production are bundled within fluid-filled cells, and these cells are wrapped in ordered sleeves of fibrous collagen. Recent models suggest that the mechanical interaction between the intracellular fluid and extracellular collagen is essential to force production in passive skeletal muscle, allowing the material stiffness of extracellular collagen to contribute to passive muscle force at physiologically relevant muscle lengths. Such models lead to the prediction, tested here, that expansion of the fluid compartment within muscles should drive forceful muscle shortening, resulting in the production of mechanical work unassociated with contractile activity. We tested this prediction by experimentally increasing the fluid volumes of isolated bullfrog semimembranosus muscles via osmotically hypotonic bathing solutions. Over time, passive muscles bathed in hypotonic solution widened by 16.44 ± 3.66% (mean ± s.d.) as they took on fluid. Concurrently, muscles shortened by 2.13 ± 0.75% along their line of action, displacing a force-regulated servomotor and doing measurable mechanical work. This behaviour contradicts the expectation for an isotropic biological tissue that would lengthen when internally pressurized, suggesting a functional mechanism analogous to that of engineered pneumatic actuators and highlighting the significance of three-dimensional force transmission in skeletal muscle.