Weibao Kong

Enhancement of biomass and hydrocarbon productivities of Botryococcus braunii by mixotrophic cultivation and its application in brewery wastewater treatment.

Successful production of mixotrophic algae allows the integration of both photosynthetic and heterotrophic components during the diurnal cycle. This reduces the impact of biomass loss during dark respiration and decreases the amount of organic substances utilization during growth; these features infer that mixotrophic production can be an important part of the microalgae to biofuels process. Mixotrophic mode provides an effective way to cultivate Botryococcus braunii with high cell density and short cultivation cycle because exogenous carbon sources, in especial, organic carbon sources, such as sodium acetate, glucose and sucrose can stimulate the biomass production of the alga remarkably. The biomass and hydrocarbon volumetric productivities were promoted significantly by the mixotrophic cultivation of B. braunii compared with the photoautotrophic group, even though the hydrocarbon contents under mixotrophic conditions were not increased in pace with the biomass contents. The present study suggested that coupling the cultivation of mixotrophic microalgae and organic wastewater treatment is a potential way to produce microalgae biomass, accumulate hydrocarbon and remove organic and inorganic salts.

Activities of Key Enzymes in the Biosynthesis of Poly-3-Hydroxybutyrate by Methylosinus trichosporium IMV3011

Abstract The activities of the key enzymes involved in the intracellular poly-3-hydroxybutyrate (PHB) synthesis of Methylosinus trichosporium IMV3011 were studied under various cultivation conditions. The enzymes were methane monooxygenase (MMO), β-ketothiolase, acetoacetyl-CoA reductase, PHB synthetase, and PHB depolymerase. Each enzyme had a unique catalytic mechanism. MMO activity decreased continuously with PHB production, but PHB at a high concentration was beneficial for maintaining MMO activity because more NADH was released by PHB depolymerization. The important reaction for entering the PHB cycle was catalyzed by β-ketothiolase. The monomer of β-hydroxybutyrate was synthesized by the catalysis of β-ketothiolase and acetoacetyl-CoA reductase. PHB synthetase played an important role in the PHB synthesis routes. The activity of PHB synthetase increased with PHB production. The changes of enzyme activities involved in PHB synthetase and PHB depolymerase occurred together, which indicated that the polymerization and depolymerization of intracellular PHB occurred simultaneously. The molecular weight of PHB was determined mainly by the combined actions of PHB synthetase and PHB depolymerase. Some important intermediates in the tricarboxylic acid cycle were helpful for PHB production because they increased related enzyme activities in the PHB cycle.

Synthesis of Polyhydroxyalkanoates by Polymerization of Methyl 3-Hydroxypropionate in the Catalysis of Lipase

The polymerization of methyl 3-hydroxypropionate as monomer catalyzed by lipase was selected as a model system in this study. The monomer with the purity around 95% could be polymerized to polyhydroxyalkanoates in the catalysis of Novozym 435. Decreasing the reaction pressure would result in the increase of product yield and high molecular weight. By choosing appropriate organic solvents, surfactants and reaction pressure, the molecular weight of polyhydroxy propionate polyester could be controlled from 1800 to 13000 (Mw value). The reusing ability of enzymatic catalyst was comparatively good. The relative activity could be maintained above 95% after 6 repeated batches reaction.