Fermentative Metabolism of Hydrogen-evolving Chlamydomonas moewusii

Abstract

The anaerobic metabolism of Chiamydomonas moewusii under both light (160 lux) and dark conditions has been examined using manometric and enzymic techniques. During anaerobiosis starch is broken down to glycerol, acetate, ethanol, C02, and H2. The release of CO2 and H2 comes to an end when the starch pool is depleted. There are only slight differences in the ratio of the end products of fermentation between light and dark metabolism. In the light, glycerol production is diminished and H2 evolution is enhanced, whereas the production rate of all other end products generally does not change. Chlamydomonas moewusii belongs to a group of unicellular green algae which are capable of utilizing or evolving molecular hydrogen (6, 9, 14). The evolution of H2 arises in darkness or in light, if the cells are exposed to anaerobiosis in an atmosphere of N2 or inert gas. There have been several suggestions to explain this H2 evolution as part of the fermentative metabolism of green algae. In their first paper about H2 production in Scenedesmus Gaffron and Rubin (7) suggested that the evolution of H2 depends at least in the dark on the degradation of a reserve substance. Exogenous glucose, which was fermented to lactic acid, increased the rate of H2 evolution. Damaschke (5) got similar results with Chlorella pyrenoidosa, which also produced lactic acid during fermentation and which could be stimulated by glucose too. For Chlamydomonas Healey (9) proposed a fermentative process including the citric acid cycle as source for H2 evolution in the dark. He assumed that the surplus NADH could either reduce some unknown acceptor or bring its electrons to a higher redox level at the expense of ATP from where H2 would be released. Under light conditions NADH should give its electrons by a light-driven reaction through the electron transport chain of photosyn-thesis to hydrogenase. This idea ofa light-driven electron transport from HADH to hydrogenase has been supported by Ben-Amotz and Gibbs (1) and King et al. (13), who assumed plastoquinone to be the site of NADH oxidation. A similar mechanism for the light-dependent evolution of H2 by Scenedesmus has been proposed by Kaltwasser et al. (1 1), who also started to elucidate the fermentation of Scenedesmus. To evaluate the validity of all of these suggested mechanisms for the evolution of H2 it seems necessary to know first the anaerobic metabolism of green algae. This includes the measurement of substrates and end products of fermentation in algae. This paper presents a first approach to the metabolism of C. moewusii under conditions of H2 evolution. 'This work was supported by Landesamt fur Forschung NRW. MATERIALS AND METHODS C. moewusii, strain 11-5/10, from the Pflanzenphysiologisches Institut der Universitat Gottingen was grown and harvested as described elsewhere (14). Concentrated cell suspensions (6 x 107 cells/ml) were used throughout all experiments. Illumination was provided by two fluorescent lamps (Philips TL 40W-1/32) where necessary; the light intensity at the surface of t...

Fermentative Metabolism of Chlamydomonas reinhardii

“…Since it represents a small percentage of the total distribution, it was not investigated further. Protein synthesis in algae adapted to an anaerobic metabolism has been demonstrated by Klein and Betz (24).…”

Fermentative Metabolism of Chlamydomonas reinhardtii

“…Classical glycolysis followed by subsequent metabolism of the pyruvate to the various end-products has been proposed to account for the anaerobic catabolism of starch or glucose in the green algae (17,19,27). Except for H2 evolution, the effect of light on fermentative carbon flow has received little attention.…”

“…The stoichiometry in the dark indicates that starch is degraded via the glycolytic pathway, and pyruvate is broken down into acetyl- (3,19,20,28).…”

“…In all conditions in the light, ethanol is a minor product. Formate production is least affected by light.The stoichiometry in the dark indicates that starch is degraded via the glycolytic pathway, and pyruvate is broken down into acetyl- (3,19,20,28).Classical glycolysis followed by subsequent metabolism of the pyruvate to the various end-products has been proposed to account for the anaerobic catabolism of starch or glucose in the green algae (17,19,27). Except for H2 evolution, the effect of light on fermentative carbon flow has received little attention.…”

“…In addition to H2, one or more of the following end-products of algal carbohydrate (endogenous starch or exogenous glucose) fermentation ' Supported by Department of Energy DE-AC02-76-ER03231 and National Science Foundation PCM 79-22612. 2Supported partially with grants from Fonds National Suisse de la Recherche Scientifique and Holderbank Stiftung. have been detected: C02, formate, acetate, ethanol, lactate, glycerol, and butanediol (3,19,20,28).…”