Flux balance analysis for overproduction of organic acids by Synechocystis sp. PCC 6803 under dark anoxic condition

The enhancement of energy supply in syngas-fermenting microorganisms

After the second industrial revolution, social productivity developed rapidly, and the use of fossil fuels such as coal, oil, and natural gas increased greatly in industrial production. The burning of these fossil fuels releases large amounts of greenhouse gases such as CO2, which has caused greenhouse effects and global warming. This has endangered the planet's ecological balance and brought many species, including animals and plants, to the brink of extinction. Thus, it is crucial to address this problem urgently. One potential solution is the use of syngas fermentation with microbial cell factories. This process can produce chemicals beneficial to humans, such as ethanol as a fuel while consuming large quantities of harmful gases, CO and CO2. However, syngas-fermenting microorganisms often face a metabolic energy deficit, resulting in slow cell growth, metabolic disorders, and low product yields. This problem limits the large-scale industrial application of engineered microorganisms. Therefore, it is imperative to address the energy barriers of these microorganisms. This paper provides an overview of the current research progress in addressing energy barriers in bacteria, including the efficient capture of external energy and the regulation of internal energy metabolic flow. Capturing external energy involves summarizing studies on overexpressing natural photosystems and constructing semiartificial photosynthesis systems using photocatalysts. The regulation of internal energy metabolic flows involves two parts: regulating enzymes and metabolic pathways. Finally, the article discusses current challenges and future perspectives, with a focus on achieving both sustainability and profitability in an economical and energy-efficient manner. These advancements can provide a necessary force for the large-scale industrial application of syngas fermentation microbial cell factories.

High-throughput profiling of metabolic responses to exogenous nutrients in Synechocystis sp. PCC 6803

Cyanobacteria fix carbon dioxide and release carbon-containing compounds into the wider ecosystem, yet they are sensitive to small metabolites that may impact their growth and physiology. Several cyanobacteria can grow mixotrophically, but we currently lack a molecular understanding of how specific nutrients may alter the compounds they release, limiting our knowledge of how environmental factors might impact primary producers and the ecosystems they support. In this study, we develop a high-throughput phytoplankton culturing platform and identify how the model cyanobacterium Synechocystis sp. PCC 6803 responds to nutrient supplementation. We assess growth responses to 32 nutrients at two concentrations, identifying 15 that are utilized mixotrophically. Seven nutrient sources significantly enhance growth, while 19 elicit negative growth responses at one or both concentrations. High-throughput exometabolomics indicates that oxidative stress limits Synechocystis' growth but may be alleviated by antioxidant metabolites. Furthermore, glucose and valine induce strong changes in metabolite exudation in a possible effort to correct pathway imbalances or maintain intracellular elemental ratios. This study sheds light on the flexibility and limits of cyanobacterial physiology and metabolism, as well as how primary production and trophic food webs may be modulated by exogenous nutrients.IMPORTANCECyanobacteria capture and release carbon compounds to fuel microbial food webs, yet we lack a comprehensive understanding of how external nutrients modify their behavior and what they produce. We developed a high throughput culturing platform to evaluate how the model cyanobacterium Synechocystis sp. PCC 6803 responds to a broad panel of externally supplied nutrients. We found that growth may be enhanced by metabolites that protect against oxidative stress, and growth and exudate profiles are altered by metabolites that interfere with central carbon metabolism and elemental ratios. This work contributes a holistic perspective of the versatile response of Synechocystis to externally supplied nutrients, which may alter carbon flux into the wider ecosystem.

Controlling average number of photons received per biomass to promote the growth of Synechocystis sp. PPC 6803

To investigate the actually received light of cells in the photo bioreactor, a light attenuation model of Synechocystis sp. PCC 6803 was established. The relationship between the average number of photons received per biomass (APRPB) and the growth of cell was analyzed. The results demonstrated, Cornet model was accurately fitted with the light attenuation of Synechocystis sp. PCC 6803 and the cell growth rate was affected by APRPB. When the value of APRPB is 3.2 μmol g^-1 s^-1, the cell have the maximum light efficiency. A maximum specific growth rate of 0.05 h^-1 was achieved with APRPB from 3.2 to 12.8 μmol g^-1 s^-1. After 156 h cultivation, compared to cells cultured under constant light [light intensity: 100 and 1800 μmol/(m² s)], the DCW under controlled light intensity (light intensity increasing with the cell density) was higher by 79.1% and 20.0%, respectively. This study indicated that APRPB could be used as a light intensity regulation criterion to improve cell production despite different types of reactor and cell density, which provided a theoretical basis for improving the biomass yield of Synechocystis sp. PCC 6803 or other photosynthetic auto-trophic organism.