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Growing concerns over greenhouse gas emissions and energy insecurity caused by the depletion of conventional fuels have led to a search for sustainable fuel alternatives. As an alternative energy carrier, hydrogen (H 2) is particularly attractive as only water is released during combustion. The process of H 2 production from genetically engineered phototrophic microorganisms through biophotolysis leads the way to solve energy shortages. Genetically engineered cyanobacteria species are potential candidates due to their superior properties for reducing greenhouse gases and using solar energy as an energy source. The review discusses the mechanisms and enzymes involved in H 2 production by cyanobacteria and applications of genetic engineering. A critical analysis of the fundamental issues attributed to the technical advancement of photobiological cyanobacteria-based H 2 production is provided, as well as the perspectives for future research to reduce carbon dioxide emissions through the creation of waste-free technology. • Genetic engineering findings of cyanobacterial nitrogenase enzyme are described. • Recent genetic engineering methods to obtain hydrogenase mutants are discussed. • Engineering photosynthetic H 2 production is shown as an efficient method. • Development of a non-waste H 2 production technology is explained. [ABSTRACT FROM AUTHOR]

The energy of cyanobacterial hydrogen (H 2) produced via bio-photolysis is being investigated as a potential solution to early-century environmental challenges. The main limiting factors of cyanobacterial H 2 photoproduction are the availability of electrons for [NiFe]-hydrogenase (H 2 ase) and the suppression of bidirectional H 2 ase activity induced by O 2 acquired from water molecules splitting in photosystem II. The current study investigated how photosynthetic inhibitors (PIs) affected H 2 production in non-N 2 -fixing cyanobacteria. Study findings revealed a rather high H 2 yield in Synechocystis sp. PSU 1262, as well as a beneficial (14.2-fold) influence of 500 μmol KCN on the H 2 production by the aforesaid strain. A 12/6-h light/dark cycle increased H 2 production by 80.3% in cells supplemented with 500 μmol KCN. Under the optimised conditions, the photobiological H 2 production of Synechocystis sp. PSU 1262 increased from 49.6 to 1552 nmol H 2 mg−1 Chl a h−1. PIs suppressed chlorophyll a concentration under illumination, lowering the O 2 levels, which enhanced bidirectional H 2 ase activity in Synechocystis sp. PSU 1262 cells. Applying varied light modes, preceded by the incorporation of PIs at optimal concentrations in H 2 production by research cyanobacterial strains, improved the H 2 yield and contributed significantly to the research originality. [Display omitted] • Six species of cyanobacteria from different ecosystems were isolated and identified. • The H 2 -producing activity of the strains was studied in the dark and in the light. • The effect of four inhibitors of photosynthesis on H 2 production was studied. • The effect of light and dark modes was evaluated on H 2 production by cyanobacteria. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen is a promising alternative to fossil fuel for a source of clean energy due to its high energy content. Some strains of phototrophic microorganisms are known as important object of scientific research and they are being explored to raise biohydrogen (BioH 2) yield. BioH 2 is still not commonly used in industrial area because of the low biomass yield and valuable down streaming process. This article deals with the methods of the hydrogen production with the help of two large groups of phototrophic microorganisms – microalgae and cyanobacteria. Microalgal hydrogen is environmentally friendly alternative to conventional fossil fuels. Algal biomass has been considered as an attractive raw source for hydrogen production. Genetic modified strains of cyanobacteria are used as a perspective object for obtaining hydrogen. The modern photobioreactors and outdoor air systems have been used to obtain the biomass used for hydrogen production. At present time a variety of immobilization matrices and methods are being examined for their suitability to make immobilized H 2 producers. Graphical abstract Image 1 Highlights • Hydrogen production from microalgae and cyanobacteria. • Mechanisms of biohydrogen metabolism. • Bioreactors for biohydrogen production process. • Enzymes of biohydrogen production. [ABSTRACT FROM AUTHOR]

Recently, there has been a propensity to postpone dealing with the world's climate concerns until later, resulting in a 1.5 °C rise in temperature over the last century. Therefore, interest in biologically derived, inexhaustible energy sources based on solar energy is growing. Cyanobacteria have the potential to produce clean, renewable fuels in the form of hydrogen (H 2) gas, derived from solar energy and water. The current study reports the screening 11 cyanobacterial strains isolated from rice paddies and hotsprings for efficient H 2 producers. According to our findings, H 2 concentrations in the species ranged from 3.6 to 48.9 μmol mg−1 Chl a h−1. H 2 production by isolated species was shown to have a 2% positive influence on oxygen (O 2) and carbon dioxide (CO 2) concentrations and a 2% negative effect on all nitrogen gas (N 2) concentrations. It was discovered that at high CO 2 concentrations, photosynthesis is enhanced but H 2 production is suppressed. Anabaena variabilis BTA-1047 was found to be the most active H 2 -producing species, with an H 2 production activity of 21.3 μmol mg−1 Chl a h−1. Moreover, a 1% O 2 : 2% CO 2 gas mixture doubled the strain activity of H 2 production. The findings of the study called into the question the notion that only an anaerobic environment is required for H 2 production by N 2 -fixing cyanobacterial species and explored whether H 2 productivity can be increased by stimulating the micro-anaerobic environment with a carbon source. [Display omitted] • Eleven nitrogen fixing cyanobacteria species were isolated and identified from different ecosystems. • Four cyanobacterial strains were distinguished by nitrogenase activity and hydrogen production. • 2% CO 2 and O 2 gases influence was favorably for most strains to produce molecular hydrogen. • Supply with 1% O 2 :2% CO 2 gas ratio increased H 2 production activity in Anabaena variabilis BTA-1047 by 2-fold. [ABSTRACT FROM AUTHOR]

Due to the side effects of greenhouse gases, interest in alternative energy sources is growing, and research into hydrogen (Н 2) production from cyanobacteria has become a promising direction for the industry. The article provides an overview of cyanobacterial hydrogen production strategies and their current economic efficiency. It also describes metabolic, genetic and technical methods for obtaining H 2 from cyanobacteria. Cyanobacteria are considered potential producers of hydrogen energy that will be economically viable shortly, as they only need cheap salts, water and solar energy to grow. However, producing hydrogen from cyanobacteria still requires extensive work, and the main problem is the small amount of hydrogen energy obtained. To produce large amounts of cyanobacterial hydrogen, the most active wild-type strains must be selected and technological, modular and genetic research must be carried out simultaneously. The low energy efficiency of hydrogen from cyanobacteria also shows the need for comprehensive research through international programs. [Display omitted] • This review shows hydrogen production mechanisms by cyanobacterial cells. • Importance of biohydrogen production strategies is discussed. • Cyanobacterial hydrogen production factors were analyzed. • Trends and problems for developing cyanobacterial hydrogen production is showed. [ABSTRACT FROM AUTHOR]

Due to the depletion and increasing cost of fossil fuels, the production of cyanobacteria-based hydrogen as eco-friendly and renewable energy for the future seems promising. The paper describes the current state of research in the field of hydrogen yield by cyanobacteria. The use of cyanobacteria as potential producers of hydrogen is particularly relevant and beneficial as they form hydrogen from water as a result of solar energy conversion. However, production is a complex biotechnological process, and the main obstacle is the low ability of cyanobacteria to produce hydrogen. The prospects for the development of cyanobacterium-based hydrogen energy can be improved by a complex approach of increasing hydrogen productivity by cyanobacteria cells. First of all, it is the achievement of genetic engineering, the construction of genetic mutants of cyanobacteria with great potential in hydrogen production, followed by a correctly chosen metabolic approach to increase its yield and the development of innovative methods of their cultivation. Thus, the widespread adoption of this technology requires additional R&D with large investments. Image 1 • Critically reviews the cyanobacterial hydrogen production. • Bioprocesses of hydrogen formation by cyanobacterial cells. • Genetic and metabolic engineering approaches towards H 2 production from cyanobacteria. • Recent technological progress towards cyanobacteria-based hydrogen production. [ABSTRACT FROM AUTHOR]