Cyanobacterial H2 production ? a comparative analysis

Abstract

Several unicellular and filamentous, nitrogen-fixing and non-nitrogen-fixing cyanobacterial strains have been investigated on the molecular and the physiological level in order to find the most efficient organisms for photobiological hydrogen production. These strains were screened for the presence or absence of hup and hox genes, and it was shown that they have different sets of genes involved in H(2) evolution. The uptake hydrogenase was identified in all N(2)-fixing cyanobacteria, and some of these strains also contained the bidirectional hydrogenase, whereas the non-nitrogen fixing strains only possessed the bidirectional enzyme. In N(2)-fixing strains, hydrogen was mainly produced by the nitrogenase as a by-product during the reduction of atmospheric nitrogen to ammonia. Therefore, hydrogen production was investigated both under non-nitrogen-fixing conditions and under nitrogen limitation. It was shown that the hydrogen uptake activity is linked to the nitrogenase activity, whereas the hydrogen evolution activity of the bidirectional hydrogenase is not dependent or even related to diazotrophic growth conditions. With regard to large-scale hydrogen evolution by N(2)-fixing cyanobacteria, hydrogen uptake-deficient mutants have to be used because of their inability to re-oxidize the hydrogen produced by the nitrogenase. On the other hand, fermentative H(2) production by the bidirectional hydrogenase should also be taken into account in further investigations of biological hydrogen production.

Rewiring hydrogenase-dependent redox circuits in cyanobacteria

“…4B and 5). Although the presence of at least two distinct (i.e., light-dependent and light-independent) pathways for electron transfer to hydrogenases have been well documented (9,36,49), to our knowledge there have been no previous reports of genetic means to enhance the rate of one pathway relative to the other. Rewiring the flow of reducing equivalents by such a strategy may not only be useful for reducing the cost of bioreactor design (i.e., by reducing the need for illumination, and associated light penetration and heat distribution issues), but also open the possibility of importing parallel redox pathways that are partially insulated from host redox machinery (Fig.…”

“…Similarly, our strain produces hydrogen at greater rates (2.8 μmol H 2 h −1 · mg Chl-a −1 ) than those reported in most other non-nitrogen-fixing unicellular cyanobacteria (0.02-1 μmol H 2 h −1 · mg Chl-a −1 (8), with the exception of Synechosystis sp. PCC 6803 when engineered (21) or under nitrogen-depleted conditions (9) (6-30 μmol H 2 h −1 · mg Chl-a −1 ), which brings S. elongatus hydrogen production rates nearer to those of many nitrogen-fixing cyanobacteria and algae (approximately 2-70 μmol H 2 h −1 · mg Chl-a −1 (9,10,43). Given the relative ease of transformation of S. elongatus, it may be possible to make further genetic modifications in this strain analogous to those demonstrated in other cyanobacteria or algae that increase starch accumulation (44), reduce cyclic electron transport (20), modify PSII activity (45), or reduce phycobilisome size (46) to allow for enhanced production of hydrogen.…”

“…The hydrogen production capacity of a variety of cyanobacterial and algal species has been surveyed (8)(9)(10), and the highest rates of hydrogen evolution are typically observed in algae and some nitrogen-fixing cyanobacteria. Algal species frequently possess [FeFe]-hydrogenases that accept low-potential electrons from ferredoxins that are, in turn, linked to the light reactions of photosynthesis (11).…”

Genetic Engineering of Cyanobacteria to Enhance Biohydrogen Production from Sunlight and Water

“…Elimination of Hup activity resulted in a 4-to 7-fold increase in the rates of H 2 production in an Ar atmosphere compared with wild-type cells, while the effects of inactivation of Hox activity on H 2 production were not evident under the conditions tested. Hup-disrupted mutants also were shown to be effective in enhancing H 2 production by several other Anabaena and Nostoc strains of cyanobacteria (Happe et al 2000;Lindberg et al 2002;Schütz et al 2004;Carrasco et al 2005;Yoshino et al 2007). A promising approach to further improve photobiological H 2 production in the presence of O 2 is to initially select parental strains with high nitrogenase activity and inactivate their Hup activities.…”

Molecular Biology of Microbial Hydrogenases

“…In cyanobacteria, the soluble NAD(P)-dependent bidirectional [NiFe]-H 2 ase is using protons to reoxidize the pyridine nucleotides reduced during dark anaerobic metabolism (Stal and Moezelaar, 1997;Troshina et al, 2002). In the cyanobacterium Synechocystis PCC 6803, the bidirectional H 2 ase produces signifi cant amounts of H 2 in the dark, in anaerobiosis (Schütz et al, 2004;Cournac et al, 2004), the rate of H 2 production being higher in the presence of fermentative substrates such as glucose. A mutant lacking the NADPH-dehydrogenase complex (NDH-1), impaired in CO 2 uptake and CO 2 fi xation was shown to produce H 2 in the light using electrons gained by water photolysis (Cournac et al, 2004).…”