Effect of kelp waste extracts on the growth and lipid accumulation of microalgae
Introduction
Microalgae are widely considered as a potential biofuel feedstock, due to their simple cell structures, easy cultivation, highly adaptive capacity, high lipid contents, as well as lipid composition suiting for biodiesel production (Hu et al., 2008, Woodworth et al., 2015). Developing microalgal oils might become a new way of biodiesel industry (Leite et al., 2013). However, high production costs seriously limit the development of microalgal biodiesel production (Acien et al., 2012). To reduce the production costs, it is necessary to obtain high biomass and lipid productivity of microalgae, and the lipid productivity and contents of fatty acids could be improved by optimization of culture conditions (Hu et al., 2008). Microalgae also accumulate a substantial amount of other valuable compounds, such as protein, carbohydrates, dietary fibers, vitamins, pigments and minerals (Thiruvenkadam et al., 2015), which could be used as feedstock for high-value products, such as food, animal feed, cosmetics, therapeutics, etc. (Markou and Nerantzis, 2013, Spolaore et al., 2006). Exploring these high-value byproducts can also efficiently decrease production costs.
Kelp is extensively used as a subsidiary food, a fertilizer and a source of alginate, mannitol and iodine, and the worldwide intensive requirement for alginate production calls for massive kelp (Tseng, 2001). In general, the extracting efficiency of alginate from kelp is only 30% (Yue et al., 2014), producing large amounts of solid residues. These solid wastes are directly released by the way of landfill, which leads to serious waste of resources and a large amount of land being occupied (Zhang et al., 2010). Kelp residues contain a mass of crude fiber, protein and residual alginic acid, the degradation of these constituents could provide massive organic nutrients and nutrient salts, which could stimulate plant or microbial growth (Möller and Smith, 1998, Zhang et al., 2010). Due to the direct or indirect stimulating effects on plant metabolism, seaweed extracts have been considered as plant biostimulants (Arioli et al., 2015). Conversion of kelp residues into biostimulants facilitates the reuse of solid waste.
The commercial cultivation of microalgae required substantial amounts of available nutrients. Reuse of the waste materials to culture microalgae for biodiesel production is alternative solution to promote the industries toward sustainable development (Lam and Lee, 2012a). Enzymatic hydrolysis has been considered as an important method of fermentable sugar production from biomass waste (Karemore et al., 2013). To probe the effects of kelp waste extracts (KWE) on the growth and lipid accumulation of microalgae, the enzymatic extracts of kelp residues were obtained by the cellulase, pectinase and papain. And several microalgal species of Chlorella sp. (Chlorella-Arc), Chlorella sorokiniana, Phaeodactylum tricornutum and Spirulina maxima were cultured by the different concentration of KWE. The impacts of KWE on the growth and biochemical composition of tested algal strains were investigated with respect to cell density, intracellular soluble sugar contents, lipid contents and fatty acid compositions. This research aims to reutilize the kelp residues to explore an alternative low-cost method to produce algal lipids.
Section snippets
Algal strains and cultivation conditions
Four algal strains, the Arctic Chlorella sp. (Chlorella-Arc) and C. sorokiniana, P. tricornutum and S. maxima, were used in this experiment. Chlorella-Arc was isolated from the glacier melted water, which was collected near the China’s Yellow River Station in NyAlesund area (78°55′ N; 11°56′ E), Spitsbergen Islands (Svalbard, Norway). Other strains were provided by Institute of Hydrobiology, Chinese Academy of Sciences. Chlorella strains were cultured in Bold’s Basal medium (BBM) (Najafabadi et
Composition of KWE
As shown in Table 1, KWE contained abundant nutrients, including amino acids, soluble sugars and diverse mineral elements. Reducing sugars were the main components in the total soluble sugars, which accounted for 84.30% of total sugars. Nitrogen (N) was the most abundant macroelement in KWE, followed by phosphorus (P), magnesium (Mg), calcium (Ca) and potassium (K). The total trace elements contents were 15.03 mg/L. In general, the organic carbon sources, such as glucose, fructose and sucrose,
Conclusions
This is the first study illustrating the effects of KWE on the physiological and biochemical responses of different microalgae, which does not cause extensive concerns in other researchers. This research found 8.0% KWE greatly improved the biomass productivities, neutral lipid and total lipid contents of Chlorella-Arc and C. sorokiniana. KWE improved the microalgal biodiesel characteristics via enhancing SFA and MUFA accumulation and reducing PUFA production. These excellent features and its
Acknowledgements
The authors are grateful for the financial support from Hi-Tech Research and Development Program of China (No. 2012AA021706), Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Co-Innovation Center for Jiangsu Marine Bio-Industry Technology, National Natural Science Foundation of China (31500318) and China Postdoctoral Science Foundation Funded Project (Nos. 2015M571764 and 2014M561661).
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