Microalgae are attractive feedstocks for producing renewable biofuels. In this dissertation, I developed a two-stage heterotrophic and phototrophic microalgae culture system for biofuel production. Heterotrophic cultures could not only serve as seed for subsequent phototrophic growth, but also produce microalgal biomass and lipid separately by feeding with organic wastes.;I demonstrated that the heterotrophically cultured microalga Chlorella sorokiniana was more efficient to be used as seed for subsequent phototrophic growth, due to the higher productivity and similar performance compared with its phototrophic counterpart. High inoculation of heterotrophically produced seeds was a potential tool for contamination control.;High cell density heterotrophic cultivation of C. sorokiniana was achieved through two-stage fed-batch fermentation. With the optimized culture conditions, the algal biomass and lipid reached high concentrations of 103.8 g L-1 and 40.2 g L-1. The lipid of C. sorokiniana contained a large amount of neutral lipids (92.9% of total lipids), triacylglycerols (82.8% of neutral lipids), and high contents of palmitic, oleic and linoleic acids, which were desirable feedstocks for biofuel production.;I evaluated the feasibility to culture C. sorokiniana for lipid production with cellulosic materials through a simultaneous saccharification and fermentation (SSF) process. The culture with substrate loading of 3% (w/v) and enzyme loading of 30 FPU/g cellulose was an appropriate combination for lipid production. Elevated temperature improved the SSF efficiency and the highest lipid concentration (2.98 g L-1), yield (99.2 mg g -1) and productivity (20.7 mg L-1 h-1) were achieved at 40°C.;I studied D-xylose uptake and the related metabolism in C. sorokiniana . The sugar uptake kinetic analysis suggested that an inducible hexose symporter might be responsible for the transport of D-xylose. The maximum D-xylose transport rate was 3.8 nmol min-1 mg-1 cell with Km value of 6.8 mM. The enzymatic activities of NAD(P)H-linked xylose reductase (XR) and NADP+-linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana. Culturing C. sorokiniana under light improved D-xylose utilization due to additional NADPH from the light-dependent reaction of photosynthesis. The results presented in this study suggested that the two-stage heterotrophic and phototrophic process was a promising technology for microalgal biofuels production.
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机译：微藻是用于生产可再生生物燃料的有吸引力的原料。在本文中，我开发了一种用于生物燃料生产的两阶段异养和光养微藻培养系统。异养培养物不仅可以用作后续光养生长的种子，还可以通过饲喂有机废物来分别产生微藻生物量和脂质。我证明了异养微藻小球藻小球藻更有效地用作后续光养生长的种子，与光养产品相比，具有更高的生产率和相似的性能。高接种异养种子是控制污染的潜在工具。通过分两批分批分批发酵实现了高细胞密度异养梭状芽胞杆菌的培养。通过优化的培养条件，藻类生物质和脂质达到了103.8 g L-1和40.2 g L-1的高浓度。梭菌的脂质包含大量的中性脂质（占总脂质的92.9％），三酰基甘油（中性脂质占82.8％）以及高含量的棕榈酸，油酸和亚油酸，它们是生物燃料生产的理想原料。我评估了通过同时糖化和发酵（SSF）过程用纤维素材料培养C. sorokiniana以生产脂质的可行性。具有3％（w / v）的底物负载和30 FPU / g纤维素的酶负载的培养物是脂质生产的合适组合。升高温度可提高SSF效率，并在40°C时达到最高脂质浓度（2.98 g L-1），产量（99.2 mg g -1）和生产率（20.7 mg L-1 h-1）。 C. sorokiniana中的木糖摄取和相关代谢。糖吸收动力学分析表明，诱导型己糖同向转运蛋白可能负责D-木糖的转运。 D-木糖的最大转运速率为3.8 nmol min-1 mg-1细胞，Km值为6.8 mM。 NAD（P）H-连接的木糖还原酶（XR）和NADP +-连接的木糖醇脱氢酶（XDH）的酶活性被检测到C. sorokiniana。由于光合作用的光依赖性反应会产生额外的NADPH，因此在光下培养C. sorokiniana可以提高D-木糖的利用率。这项研究提出的结果表明，两步异养和光养过程是一种用于微藻生物燃料生产的有前途的技术。
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