Bioscience Evidence 2024, Vol.14, No.2, 81-92 http://bioscipublisher.com/index.php/be 82 This study will delve into the metabolic mechanisms of anaerobic microorganisms involved in biohydrogen production, analyzing strategies to enhance hydrogen yield through genetic engineering. It will also evaluate the potential applications of these genetically modified microorganisms in advancing sustainable energy development. By providing a comprehensive overview of the metabolic pathways of anaerobic bacteria in biohydrogen production, this research offers new insights into the fundamental scientific principles of bioenergy conversion, thereby promoting innovation and advancement in biotechnology for clean energy. 2 Overview of Anaerobic Bacteria in Biohydrogen Production 2.1 Types of anaerobic bacteria involved Anaerobic bacteria are pivotal in the biological production of hydrogen due to their ability to thrive in environments devoid of oxygen, where they efficiently metabolize organic substrates into hydrogen. A variety of anaerobic bacterial species have been identified as efficient producers of biohydrogen. These bacteria are categorized based on their metabolic capabilities and the specific pathways they utilize to generate hydrogen. 2.1.1 Clostridium species Clostridium species are among the most extensively studied anaerobic bacteria for biohydrogen production. These Gram-positive, spore-forming bacteria are known for their high hydrogen yield during the fermentation of carbohydrates. Clostridium butyricumand Clostridium acetobutylicumutilize the butyrate and acetate pathways to produce hydrogen. The process involves the fermentation of glucose and other sugars into organic acids and hydrogen gas, with the production of acetate being particularly beneficial for hydrogen generation (Pason et al., 2020). 2.1.2 Enterobacter species Enterobacter species, such as Enterobacter cloacae, are facultative anaerobes that have also shown significant potential in biohydrogen production. Unlike Clostridium species, Enterobacter species can grow in both aerobic and anaerobic conditions, although hydrogen production occurs under anaerobic conditions. These bacteria utilize the formate hydrogen lyase (FHL) pathway, where formate is cleaved into hydrogen and carbon dioxide. This pathway is less energy-intensive compared to other metabolic routes, making Enterobacter species attractive candidates for biohydrogen production (Nizzy et al., 2020). 2.1.3 Other significant species In addition to Clostridium and Enterobacter species, other anaerobic bacteria have also been identified as efficient hydrogen producers. These include Thermotoga maritima and Caldicellulosiruptor saccharolyticus, both of which are thermophilic bacteria that thrive at high temperatures. These species utilize unique pathways, such as the ferredoxin-dependent hydrogenase pathway, which allows for efficient electron transfer during the breakdown of complex carbohydrates into hydrogen. The high temperature stability of these bacteria makes them particularly suited for industrial-scale biohydrogen production (Saidi et al., 2018; Ben Gaida et al., 2022). 2.2 Natural metabolic pathways for hydrogen production The metabolic pathways employed by anaerobic bacteria for hydrogen production are diverse and reflect the adaptability of these organisms to different environmental conditions (Figure 1). The primary pathways include: Ferredoxin-Dependent Hydrogenase Pathway: This pathway is commonly used by Clostridium species, where electrons generated during the oxidation of pyruvate are transferred to ferredoxin. The reduced ferredoxin then donates electrons to hydrogenase, leading to the production of hydrogen (Buckel, 2021). Formate Hydrogen Lyase (FHL) Pathway: Enterobacter species primarily use this pathway, where formate is directly split into hydrogen and carbon dioxide by the formate hydrogen lyase enzyme complex. This pathway is highly efficient in generating hydrogen under anaerobic conditions (Nizzy et al., 2020). Butyrate and Acetate Pathways: In Clostridium species, these pathways involve the fermentation of sugars into butyrate and acetate, with hydrogen being produced as a byproduct. The acetate pathway is particularly important due to its higher hydrogen yield (Amin et al., 2019).
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