Algal Hydrogen Production

Abstract

Direct photosynthetic production of hydrogen from water has the theoretical potential to totally displace gasoline used in the United States, while requiring only about 0.12% of the continental land area. This article presents an overview of the metabolic pathways and enzymes utilized by algae and other microbes to generate H 2 , the barriers currently preventing practical application of these processes, and the current research approaches under investigation to overcome these barriers. The major barrier is the sensitivity of the H 2 ‐producing catalyst ([FeFe]‐hydrogenase) to O 2 produced by photosynthesis, and a variety of approaches are being pursued to address this challenge at the molecular level. The development of photobiological H 2 ‐production systems gained worldwide attention in 2000 with the observation that sulfur‐deprived Chlamydomonas reinhardtii cultures become anaerobic in the light and photoproduce H 2 for up to 4 days. Since then this phenomenon has been explored extensively, and the results have led to major new insights into Chlamydomonas anaerobic physiology and metabolism, as well as to other potential approaches to address other barriers to the practical application of photobiological H 2 production. These other barriers, which affect H 2 ‐production efficiency, are also examined and include: (i) competition from other electron acceptors besides hydrogenases for photogenerated reductant at the level of reduced ferredoxin, (ii) down‐regulation of photosynthetic electron transport activity under H 2 ‐producing conditions, (iii) the occurrence of state transitions which waste photons, and (iv) the low light‐saturation level of photosynthesis compared to the solar resource. Additional strategies to lower the potential cost of biohydrogen from algae are also examined. They include issues associated with photobioreactors; dark, fermentative H 2 production; and various types of integrated systems, which combine both dark and light‐driven H 2 ‐production processes.

ChlamydomonasFlavodiiron Proteins Facilitate Acclimation to Anoxia During Sulfur Deprivation

“…The FDP up-regulation during the photosynthetic and respiratory phase of H 2 photoproduction indicates that O 2 photoreduction via FDPs is important in the acclimation to these conditions. It has been postulated that the decrease of O 2 after a shift to sulfur deprived medium is mainly due to an increase in mitochondrial respiration ( Melis et al 2000 , Melis 2007 , Ghirardi et al 2010 ). Our results indicate that FDPs contribute to the establishment of anaerobiosis by functioning in light-induced O 2 uptake.…”

Spectroradiometric monitoring for open outdoor culturing of algae and cyanobacteria

“…For example, biodiesel may be derived from microalgal oil [2,3], anaerobic digestion of algal biomass can yield methane among other biogas products [4,5], hydrothermal liquefaction of algae can generate biocrude [6], and photosynthetic production of hydrogen gas has been demonstrated in several algal species [7][8][9]. However, while algae-derived feedstocks are considered candidates for next-generation biofuels, in order to displace a significant portion of petroleum-based fuels, algal cultivation must occur at a scale that approaches conventional agriculture [2,10,11].…”