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Microorganisms Involved in Biofuel Production Processes
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
Unlike cyanobacteria, other photosynthetic bacteria such as purple and green bacteria are anoxygenic in nature. These organisms have innate capabilities to manifest H2 production through photofermentation by consuming a wide variety of substrates ranging from inorganic to organic substrates in the presence of light (Figure 3.2c). The photosynthetic bacteria that undergo photofermentation belong to the group of green bacteria or purple bacteria. These bacterial groups contain bacteriochlorophyll which has plant-like light-harvesting properties. However, no oxygen is produced during the process. The green bacteria such as Chlorobium limicola and Chloroflexus aurantiacus contain a photosystem I (PSI)-like photosystem which takes up light energy from sunlight and drives the photosynthesis reaction (McKinlay and Harwood 2010). These bacteria derive electrons for hydrogen production through oxidation of inorganic or organic substrates, which are further used to reduce ferredoxin. The reduced ferredoxin in turn acts as an electron donor for the nitrogenase to perform the dark reaction as well as hydrogen production. On the other hand, the purple bacteria such as Rhodobacter sphaeroides and Rhodopseudomonas palustris contain a photosystem II (PSII)-like photosystem and thus do not have the capability to reduce the ferredoxin. In these organisms, the electrons needed for nitrogenase-mediated hydrogen production are derived from the cyclic electron flow through the quinone pool (Figure 3.2c). Often, the photofermentation process is used for the treatment of wastewater and many studies suggest the integration of this technology with the dark fermentative hydrogen production process (discussion following) to enhance the overall hydrogen yields (Dasgupta et al. 2010; Harai et al. 2010; Xia et al. 2013). Despite the various efforts to improve the photofermentative hydrogen yields, the low hydrogen production rates and the economic barriers associated with the design and scale up of photobioreactors impose challenge for the commercialization of this technology.
Green hydrogen production by Rhodobacter sphaeroides
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Dahbia Akroum-Amrouche, Hamza Akroum, Hakim Lounici
Hiroyo Otaki et al. (2012) reported that the hydrogen production under illumination by the green non-sulfur bacteria Chloroflexus aggregans decreased indicating that this bacteria functions as hydrogen consumer, only one species Chloroflexus aurantiacus is identified as a hydrogen-producing bacterium (Li and Fang 2009).