Application of bacteria and bacterial biosurfactant to achieve high lipid productivity in algal cultivation = 박테리아와 박테리아 생물계면활성제를 활용한 미세조류 지질생산성 향상에 대한 연구

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Successful cultivation of algal crops at the commercial scale necessitates careful consideration of ecological communities in cultivation platforms that often include undesirable weedy algae, algal grazers, and bacteria. In Chapter 1, I first review literature on agricultural and aquatic systems with consideration of the implementations of key ecological principles in managing commercial-scale algal cultivation. The review suggests that careful management of food-web structure in algal cultivation platforms will be needed to maximize crop protection, and that temporal and spatial diversification of algal crops may also benefit industrial algal biofuels production. While the key ideas of top-down control of algal grazers and the potential advantages of diversifying algal crops have encouraged researchers to explore food-web interactions in algal cultivation platforms, the review further indicates that bacteria and bacterial metabolites can also play substantial roles in achieving sustainable production of algal biomass. In light of these findings, I further explore the less-documented influence of bacteria and bacterial biosurfactant on managing algal cultivation systems in next Chapters. In Chapter 2, I survey and isolate phycosphere bacteria of Chlorella sp. HS2 grown in inorganic growth medium. The results indicate the dominant existence of Rhizobium, a plant growth promoting bacterium (PGPB), in algal culture. The subsequent co-cultivation of axenic Chlorella sp. HS2 with Rhizobium confirms algal growth-promoting influence of this bacterium, although the lipid content of harvested biomass from Chlorella-Rhizobium co-culture system is substantially decreased. While algal growth inhibiting influence of Microbacterium, another isolated bacterium, is confirmed, this bacterium seems to enhance algal lipid content that significantly improved the lipid productivity of Chlorella-Microbacterium co-culture system. The results of Chapter 2 thus indicate that both growth-promoting and growth-inhibiting bacteria can positively contribute to enhancing algal lipid productivity compared to the axenic control, and further support that the implementation of algal-bacterial co-cultivation system must carefully consider target products (e.g., biomass vs. lipid). In addition to bacteria, herbivorous zooplanktons often colonize in open algal cultivation platforms, and their proliferation may devastate biomass production within a few days. In Chapter 3, I propose the application of a biosurfactant produced by Bacillus subtilis C9 (referred to as C9-biosurfactant) for controlling cladoceran grazers commonly found in algal cultivation systems. The results indicate that C9-biosurfactant completely eradicate Daphnia pulex and Moina macrocopa within 24 hours. Moreover, supplying C9-biosurfactant into the cultures of algal crops with and without cladoceran grazers indicates no adverse effect of C9-biosurfactant on the growth and lipid productivity of these selected algal strains, while cladocerans are selectively controlled by C9-biosurfactant even under the presence of their prey. However, to deploy C9-biosurfactant as an effective biocontrol agent for cladoceran grazers, the production costs of bacterial biosurfactant must be reduced substantially. In Chapter 4, I present a laboratory-scale demonstration of fermenting B. subtilis C9 with the acid hydrolysate of defatted Chlorella biomass (referred to hereupon as DCB). While initial hydrolysis of DCB indicates the highest yield of fermentable monosaccharides when autoclaved with 0.25 N HCl, DCB hydrolysate is deemed to be a suitable fermentation medium for the production of biosurfactant. These results thus clearly support the possibility of incorporating non-ethanol fermentation into algal biorefinery through which overall economic outlook of the nascent algae industry could be substantially improved. Overall, this dissertation suggests that bacteria and bacterial biosurfactant can be successfully implemented to achieve high and reliable production of algal biomass and lipids at industrial algal cultivation.
Chang, Yong Keunresearcher장용근researcher
한국과학기술원 :생명화학공학과,
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학위논문(박사) - 한국과학기술원 : 생명화학공학과, 2019.2,[vi, 91 p. :]


Algal lipids▼abacillus subtilis C9▼abiosurfactant▼achlorella sp. HS2▼adaphnia pulex▼adefatted chlorella biomass▼afood-web▼amoina macrocopa▼aphycosphere bacteria; 미세조류 지질▼a바실러스▼a생물계면활성제▼a클로렐라▼a물벼룩▼a지질추출된 잔사 미세조류 바이오매스▼a먹이그물▼a파이코스피어 박테리아

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