Ethanol and protein production from minimally processed biomass of a genetically-modified cyanobacterium over-accumulating sucrose

Genetic engineering for biohydrogen production from microalgae

The development of biohydrogen as an alternative energy source has had great economic and environmental benefits. Hydrogen production from microalgae is considered a clean and sustainable energy production method that can both alleviate fuel shortages and recycle waste. Although algal hydrogen production has low energy consumption and requires only simple pretreatment, it has not been commercialized because of low product yields. To increase microalgal biohydrogen production several technologies have been developed, although they struggle with the oxygen sensitivity of the hydrogenases responsible for hydrogen production and the complexity of the metabolic network. In this review, several genetic and metabolic engineering studies on enhancing microalgal biohydrogen production are discussed, and the economic feasibility and future direction of microalgal biohydrogen commercialization are also proposed.

Utilization of Biomass Derived from Cyanobacteria-Based Agro-Industrial Wastewater Treatment and Raisin Residue Extract for Bioethanol Production

Biofuels produced from photosynthetic microorganisms such as microalgae and cyanobacteria could potentially replace fossil fuels as they offer several advantages over fuels produced from lignocellulosic biomass. In this study, energy production potential in the form of bioethanol was examined using different biomasses derived from the growth of a cyanobacteria-based microbial consortium on a chemical medium and on agro-industrial wastewaters (i.e., dairy wastewater, winery wastewater and mixed winery–raisin effluent) supplemented with a raisin residue extract. The possibility of recovering fermentable sugars from a microbial biomass dominated by the filamentous cyanobacterium Leptolynbgya sp. was demonstrated. Of the different acid hydrolysis conditions tested, the best results were obtained with sulfuric acid 2.5 N for 120 min using dried biomass from dairy wastewater and mixed winery–raisin wastewaters. After optimizing sugar release from the microbial biomass by applying acid hydrolysis, alcoholic fermentation was performed using the yeast Saccharomyces cerevisiae. Raisin residue extract was added to the treated biomass broth in all experiments to enhance ethanol production. Results showed that up to 85.9% of the theoretical ethanol yield was achieved, indicating the potential use of cyanobacteria-based biomass in combination with a raisin residue extract as feedstock for bioethanol production.

Metabolic engineering of microorganisms for the production of ethanol and butanol from oxides of carbon

The utilized biomass is an important consideration for sustainable biofuel production. To avoid competing with food needs, researchers have turned their attention to non-food lignocellulosic biomasses as potential feedstocks for biofuel production. However, the saccharification of a lignocellulosic biomass produces a large amount of lignin as waste. To overcome this hurdle, biomass gasification has been suggested as an alternative to saccharification. During biomass gasification, oxides of carbon (CO, CO₂) and hydrogen are produced as a major product. Accordingly, microorganisms capable of utilizing these oxides of carbon have gained attention as hosts for the production of biofuels, such as ethanol and butanol. In this work, we reviewed the Calvin cycle and Wood-Ljungdahl pathway for utilizing oxides of carbon in cyanobacteria and acetogens, respectively, and discussed the metabolic engineering strategies that may be used to produce ethanol and butanol from oxides of carbon through these routes.