Use of algae technology for production of biohydrogen from green microalgae: Possibilities for a practical sustainable process and diversity at both species selection, culturing and gene transcript levels

Algae technology represents an extensive research field which has developed rapidlyover the last decades. The research activities extend from algae cultivation includingCO2 capture, production of commercial products such as health food, aquaculture andanimal feed, production of valuable metabolites, to conversion of solar energy intoenergy carriers like biohydrogen or biodiesel. A combination of several aspects ofalgae technology into a multidisciplinary process is proposed in this work. Valuablemetabolites produced by algae include for example carotenoids, unsaturated fattyacids, vitamins, glycerol, components with medical activities and a number ofantioxidants. Many of these are secondary metabolites produced as a response todifferent forms of environmental stress, and they may function as protectionmechanisms to avoid damage to the cells. Biohydrogen from green microalgae is anexpanding field which has made great progress through the last decade. By exposingsome species of algae to environmental stress, e.g. by depriving the algae of sulfur inlight, it is possible to produce significant amounts of hydrogen gas. However, thistechnology is still in its infancy, and there is significant potential for technologydevelopment and improvement at every level. In this study, the possibility ofproducing hydrogen from solar energy by using green microalgae is explored atspecies selection-, culturing- and gene transcription levels. It is demonstrated that thereis a considerable number of species currently known to have potential for hydrogenproduction, and the same is true for production of valuable metabolites. The effects ofdifferent stress reactions on production of the valuable components are described,along with the purpose of their production. This knowledge can be used to evaluate thepossibilities for producing hydrogen and high value products efficiently in the sameprocess. Hydrogen production under sulfur deprivation is explored in several speciesof green algae under controlled conditions, and Chlamydomonas noctigama shows theability to produce hydrogen with efficiency comparable to the model organismChlamydomonas reinhardtii. The ability to produce hydrogen under sulfur deprivationis also explored in relation to the different species’ ability to show heterotrophic ormixotrophic growth on acetate. A photobioreactor specifically designed for algae hydrogen production is described for lab scale research purposes, includingconsiderations for measurement devices and materials choice. Hydrogen productionby the algae C. noctigama is further explored at molecular level. By using RT-PCRfollowed by PCR with degenerate primers, mRNA with homology towards green algalhydrogenases was identified. The cDNA sequences were translated to putative aminoacid sequences, and analyzed in respect to amino acids characteristic for green algalhydrogenases and amino acids which share characteristics with both hydrogenases andnarf-like proteins. These results were used to evaluate the identification of the mRNAsequences found in C. noctigama. While other green algae have been shown to containtwo different hydrogenases, it is here demonstrated that C. noctigama is able totranscribe three distinct genes which share essential characteristics with hydrogenases.The combination of these results provides valuable insights at several levels of acombined process for production of biohydrogen and other valuable products. Furtherstudies of these topics may result in a sustainable process where solar energy can beconverted into hydrogen in an integrated manner, where production efficiencies aresufficient for an economic exploitation of algal technology using algal stress reactions.