High Yields of Hydrogen Production Induced by Meta-Substituted Dichlorophenols Biodegradation from the Green Alga Scenedesmus obliquus

Abstract

Hydrogen is a highly promising energy source with important social and economic implications. The ability of green algae to produce photosynthetic hydrogen under anaerobic conditions has been known for years. However, until today the yield of production has been very low, limiting an industrial scale use. In the present paper, 73 years after the first report on H2-production from green algae, we present a combinational biological system where the biodegradation procedure of one meta-substituted dichlorophenol (m-dcp) is the key element for maintaining continuous and high rate H2-production (>100 times higher than previously reported) in chloroplasts and mitochondria of the green alga Scenedesmus obliquus. In particular, we report that reduced m-dcps (biodegradation intermediates) mimic endogenous electron and proton carriers in chloroplasts and mitochondria, inhibit Photosystem II (PSII) activity (and therefore O2 production) and enhance Photosystem I (PSI) and hydrogenase activity. In addition, we show that there are some indications for hydrogen production from sources other than chloroplasts in Scenedesmus obliquus. The regulation of these multistage and highly evolved redox pathways leads to high yields of hydrogen production and paves the way for an efficient application to industrial scale use, utilizing simple energy sources and one meta-substituted dichlorophenol as regulating elements.

Potassium deficiency, a “smart” cellular switch for sustained high yield hydrogen production by the green alga Scenedesmus obliquus

“…The temperature of TCD was set at 200 C for the detector and 180 C for the injector. The quantification of hydrogen and oxygen was done by injecting known quantities in the GC-TCD [6].…”

“…Total proteins were extracted from cells, according to the method of Siminis et al [27] and [6]. Protein determination was performed according to Lowry et al [28].…”

“…An extremely high yield in hydrogen productivity appeared in Scenedesmus obliquus cultures when one meta-substituted dichlorophenols (m-dcps) was added to the culture medium [6,7]. Reduced m-dcps, according to their redox potential, take the place of electron donors in the photosynthetic electron flow, close to the PQ-pool.…”

“…Additionally, the first step of m-dcps biodegradation (the reduction of m-dcps) supports a continuous circuit between oxidized and reduced m-dcps, which promotes strong electron flow to the PQ-pool, and in turn to Fd and to hydrogenase. Oxygen depletion was achieved not only by the inhibition of PSII activity, but was also induced by the combinational transfer of electrons from reduced m-dcps to the ubiquinone of the mitochondrial respiratory mechanism (cytochromic and alternative pathways) [6,7].…”

Hydrogen production using photobiological methods

“…To overcome this problem, some researchers studied the different biochemical mechanisms of algae and cyanobacteria. Genetic engineering of green algae is considered as pioneering research to enhance H 2 gas; genetic and other biochemical modifications as well as the generation of new strains of cyanobacteria to enhance H 2 production have been applied(Bonenthe et al, 2011;Ghysels & Franck, 2010;Nguyen et al, 2011;Papazi, Andronis, Loannidis, Chaniotakis, & Kotzabasis, 2012;Philipps, Happe, & Hemschemeier, 2012;Tiwari & Pandey, 2012;Winkler, Kuhlgert, Hippler, & Happe, 2009). Some genetically modified cyanobacterial strains such as Synechococcus PCC 6301 and PCC 7942 and Synechocystis PCC 6803 have been considered good model organisms to enhance H 2 production…”