Implementation of photobiological H2 production: the O2 sensitivity of hydrogenases

Abstract

The search for the ultimate carbon-free fuel has intensified in recent years, with a major focus on photoproduction of H2. Biological sources of H2 include oxygenic photosynthetic green algae and cyanobacteria, both of which contain hydrogenase enzymes. Although algal and cyanobacterial hydrogenases perform the same enzymatic reaction through metallo-clusters, their hydrogenases have evolved separately, are expressed differently (transcription of algal hydrogenases is anaerobically induced, while bacterial hydrogenases are constitutively expressed), and display different sensitivity to O2 inactivation. Among various physiological factors, the sensitivity of hydrogenases to O2 has been one of the major factors preventing implementation of biological systems for commercial production of renewable H2. This review addresses recent strategies aimed at engineering increased O2 tolerance into hydrogenases (as of now mainly unsuccessful), as well as towards the development of methods to bypass the O2 sensitivity of hydrogenases (successful but still yielding low solar conversion efficiencies). The author concludes with a description of current approaches from various laboratories to incorporate multiple genetic traits into either algae or cyanobacteria to jointly address limiting factors other than the hydrogenase O2 sensitivity and achieve more sustained H2 photoproduction activity.

Mechanism of O2 diffusion and reduction in FeFe hydrogenases

“…11 Due to the sensitivity of FeFe hydrogenases to molecular oxygen, understanding the mechanism of O 2 inhibition is a prerequisite for using genetic engineering to increase their O 2 -tolerance. This is crucial in the case of the enzyme from Cr, since this green alga could be used for biological H 2 photoproduction 12 if its hydrogenase were less inhibited by the O 2 produced by photosynthesis.…”

Comparative study of the oxygen tolerance of Chlorella pyrenoidosa and Chlamydomonas reinhardtii CC124 in photobiological hydrogen production

“…There are several methods to induce anoxic conditions for H 2 evolution [17]. One method is to place algal cells in sulfur-deprived medium and the underlying mechanism has been intensively studied recently [18].…”

Produção de hidrogênio por <i>Chlamydomonas </i>spp. e <i>Anabaena</i> spp.

“…(VYAS; KUMAR, 1994;MCKINLAY;HARWOOD et al, 2010;GHIRARDI, 2015 (EADY, 1996;BOTHE et al, 2010;WEBER et al, 2015).…”

“…Além disso, para solucionar estes problemas, técnicas de engenharia molecular foram desenvolvidas para produzir hidrogenases mais tolerantes ao oxigênio (MCTAVISH; SAYAVEDRA- SOTO, 1995;GHIRARDI et al, 2015), beneficiando a produção de hidrogênio, aumentando a produtividade das cepas (GODAUX et al, 2013 (NEILSON et al, 1971;BOTHE et al, 2010;YEAGER et al, 2011;ANTAL et al, 2015).…”

“…Além desta perspectiva futura, veem-se também esforços na engenharia genética em desenvolver cepas com mutações genéticas, analisando-se as vantagens e desvantagens, para tornar a hidrogenase menos sensível ao oxigênio (GODAUX et al, 2013;GHIRARDI, 2015;GHIRARDI, 2015), aumento da taxa respiratória para acelerar o processo de anaerobiose (XU et al, 2014) e mutações na hidrogenase de captação das cianobactérias para diminuir o efeito da reciclagem de hidrogênio produzido pela nitrogenase (MARQUES et al, 2011;TIWARI;PANDEY, 2012;KOSOUROV et al, 2014). …”