Multiple and reversible hydrogenases for hydrogen production byEscherichia coli: dependence on fermentation substrate, pH and the F₀F₁-ATPase

Abstract

Molecular hydrogen (H(2)) can be produced via hydrogenases during mixed-acid fermentation by bacteria. Escherichia coli possesses multiple (four) hydrogenases. Hydrogenase 3 (Hyd-3) and probably 4 (Hyd-4) with formate dehydrogenase H (Fdh-H) form two different H(2)-evolving formate hydrogen lyase (FHL) pathways during glucose fermentation. For both FHL forms, the hycB gene coding small subunit of Hyd-3 is required. Formation and activity of FHL also depends on the external pH ([pH](out)) and the presence of formate. FHL is related with the F(0)F(1)-ATPase by supplying reducing equivalents and depending on proton-motive force. Two other hydrogenases, 1 (Hyd-1) and 2 (Hyd-2), are H(2)-oxidizing enzymes during glucose fermentation at neutral and low [pH](out). They operate in a reverse, H(2)-producing mode during glycerol fermentation at neutral [pH](out). Hyd-1 and Hyd-2 activity depends on F(0)F(1). Moreover, Hyd-3 can also work in a reverse mode. Therefore, the operation direction and activity of all Hyd enzymes might determine H(2) production; some metabolic cross-talk between Hyd enzymes is proposed. Manipulating of different Hyd enzymes activity is an effective way to enhance H(2) production by bacteria in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H(2) production, reduced fuels and other chemicals with higher yields than those obtained by common sugars.

Impact of membrane-associated hydrogenases on the FOF1-ATPase in Escherichia coli during glycerol and mixed carbon fermentation: ATPase activity and its inhibition by N,N′-dicyclohexylcarbodiimide in the mutants lacking hydrogenases

“…The activities of FHL and, in addition, proton-translocating F O F 1 -ATPase, key membrane enzyme of bioenergetic relevance, have been also found out to affect the fermentative metabolism of glycerol in E. coli [13,20]. Some requirement of F O F 1 and its relationship with Hyd enzymes in E. coli were suggested upon both glucose and glycerol fermentations [7,13].…”

“…The complex containing Hyd-3 (hyc) is considered as FHL-1, whereas Hyd-4 (hyf) containing complex is considered as FHL-2 [13,14]. These two FHL complexes are active upon glucose fermentation, but they might be different under glycerol fermentative conditions [13]. Besides, E. coli synthesizes the other Hyd enzymes (Hyd-1, Hyd-2), which are also functional in anaerobic fermentative conditions [13,15].…”

“…These two FHL complexes are active upon glucose fermentation, but they might be different under glycerol fermentative conditions [13]. Besides, E. coli synthesizes the other Hyd enzymes (Hyd-1, Hyd-2), which are also functional in anaerobic fermentative conditions [13,15]. Hyd-1 (hya) and Hyd-2 (hyb) oxidize H 2 during glucose fermentation and work in a reverse mode upon glycerol fermentation [6].…”

“…The complex containing Hyd-3 (hyc) is considered as FHL-1, whereas Hyd-4 (hyf) containing complex is considered as FHL-2 [13,14]. These two FHL complexes are active upon glucose fermentation, but they might be different under glycerol fermentative conditions [13].…”

“…In E. coli FHL is membrane-associated protein complex consisted of selenocysteine-and Mo-cofactor-containing formate dehydrogenase-H (Fdh-H), [Ni-Fe] hydrogenase (Hyd) and other electron-transferring components [13]. The complex containing Hyd-3 (hyc) is considered as FHL-1, whereas Hyd-4 (hyf) containing complex is considered as FHL-2 [13,14].…”