Screening of unicellular microalgae for biofuels and bioactive products and development of a pilot platform
Liu, Jianguo; Li, Qianqian; Liu, Qian; He, Meilin; Zhang, Litao; Liu, Yang Doris; Ding, Yancong; Zhang, Zhen; Lin, Wei; Song, Pingping; Li, Ling; Huang, Yuan; Han, Chunmei
Large-scale screening of wild type microalgae for favorable fast-growing oleaginous strains has been carried out in our laboratory since early 2008. Based on our rough calculation, over 30 field study trips covering routes of more than 70,000 km were launched, and over 1600 water samples were collected. More than 1200 monoclones of unicellular microalgae have been successfully isolated and purified. Of the monoclones isolated, 143 strains were selected to analyze their total lipid contents. 52 strains were used to study their abilities to produce H2 autotrophically. 11 strains were found to accumulate > 40% of total lipid per dry weight of biomass. 3 strains have the ability to accumulate > 50% of total lipid while exposed to N-deficiency. A two-stage culturing mode was developed for the three most oleaginous strains under their optimal growth conditions. Metabolic aspects of N-deprived and N-enriched Is ochrysis galbana were comparatively studied on the bioinformatic and proteomic level using two dimensional electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The results suggested that the glycolytic pathway and the citrate transport pathway both mitochondria and cytosol were the main routes for lipid anabolism in N-deprived I. galbana, and that the tricarboxylic acid cycle, the glyoxylate cycle and the sulfur assimilation system were the major pathways involved in lipid catabolism. For the screening of H2 producing microalgae, 28 of the 52 tested strains were found to evolve H2 under sulfur and/or nitrogen deprivation. The freshwater chlorophyte Chlorella protothecoides showed the highest H2 producing capacity among the tested algae. Chlorella autotrophica and Tetraselmis striata were two notable green marine species that produced H2 phototrophically. In terms of bioactive substances, Haematococcus pluvialis is an important species both for production of astaxanthin enriched bioproducts and for biofuels. More than 40 ecologically separated wild type strains and 12 mutants of H. pluvialis are cultivated in our laboratory. The complex, bi-phasic life cycle of H. pluvialis has been studied intensively. Natural astaxanthin and β-carotene from unicellular microalgae are produced in pilot and in industrial scale. A new variety of an aerial microalga, Trentepohlia aurea, was found to be widely distributed in snow covered mountains. T. aurea grows naturally on stone surfaces, dotting the stone in an array of saffron yellow and brownish red color due to its high carotenoid content (2.2% of dry weight), which effectively protect the cells from UV and photodamage in high altitude. T. aurea also has a powerful water-absorptive capacity and a unique cold and freezing resistance.