Beneficial changes in biomass and lipid of microalgae Anabaena variabilis facing the ultrasonic stress environment
Introduction
Microalgae as a suitable and promising ingredient receive worldwide attention and research due to their applications in the production of edible nutrition, feed, dye and biofuel (Demirbas and Fatih Demirbas, 2011, Kiran et al., 2014, Menetrez, 2012). Compared with the second generation biomass, microalgae take the advantages of high biomass productivity and lipid yield, widespread existence, ease of management and less space occupation (Chisti, 2007, Maity et al., 2014). In the production of biofuels, microalgae can use sunlight and carbon dioxide to synthesize lipid under stress or stimulation conditions (Suali and Sarbatly, 2012, Venkata Mohan and Devi, 2014). The formed lipid as energy storage enables the microalgae cells endure the harsh environment and can be transesterified to produce biodiesel (Rawat et al., 2013). Improving the lipid content is a feasible way to maximize the biodiesel production by optimizing the cultivation conditions, designing efficient reactors and cultivation model and subjecting the algae to stress environments (Dogaris et al., 2015, Han et al., 2015, Rodolfi et al., 2009, Skorupskaite et al., 2015). The most common stress environments used are nutrients depletion, high temperature and light, pH values, salinity concentration (Venkata Mohan and Devi, 2014). Several studies have also mentioned the effects of ultrasonic exposure on the microalgae growth and intracellular compounds synthesis (Rajasekhar et al., 2012, Tang et al., 2004).
Ultrasonic is the sound waves of a frequency at or above 20 kHz. The caused compression and rarefaction cycles in water by the ultrasound radiation lead to the generation of cavitation bubbles or cavitation effect (Suslick, 1990). Millions of these produced bubbles can create implosive collapse accompanied by yielding localized extreme temperatures as high as 5000 °C, high pressures of 100 MPa and free radicals (Rajasekhar et al., 2012). The external conditions can induce the change of components synthesis including lipid, carbohydrate, protein and chlorophyll. Some researchers focus on the nitrogen starvation which can induce the lipid accumulation but limit the cell proliferation, nutrients utilization and carbon fixation (Khozin-Goldberg and Cohen, 2006, Rezanka et al., 2011, Zhou et al., 2014). The nitrogen starvation being time-consuming is usually applied throughout the growing period or the lipid-inducing cultivation phase. High salinity and temperature can induce lipid accumulation during the late cultivation time in a two-stage culture strategy (Venkata Mohan and Devi, 2014). Although few studies have tried to test the effects of ultrasonic on lipid accumulation of microalgae, ultrasonic wave has been used in controlling algae bloom, assisting lipid extraction and testing the effects on growth (Greenly and Tester, 2015, Lee et al., 2001, Ma et al., 2014, Rajasekhar et al., 2012, Tang et al., 2004). Ultrasonic wave can change the permeability of the membrane which affects the nutrients utilization leading to the variation of cell activity and material synthesis (Joyce et al., 2013, Tang et al., 2004). Hao et al. (2004) have observed the different effects of ultrasonic irradiation on the phycocyanin and chlorophyll a of Spirulina platensis at the frequencies of 20 kHz and 1.7 MHz. In a related study, Rajasekhar et al. (2012) investigated the growth of three species after sonication showing different membrane damage degree and ability in resistance to ultrasonic. The results showed that algae with gas-vacuolate and thin cell wall were more likely to be affected by the ultrasonic irradiation. Most of these works have focused on the harmful and inhibition effects of cells and growth under ultrasonic exposure; only little information is referred about the beneficial aspects of ultrasonic in microalgae growth. However, to our knowledge the researches have rarely focused on the beneficial effects of ultrasonic as a stress cultivation condition on the lipid accumulation of algae during the growth.
In this study, different ultrasonic treatment powers and times are tested to determine the biomass and lipid accumulation changes of the microalgae strain Anabaena variabilis. The selected strain is filamentous algae the morphological change of which can be easily observed under the microscope. Moreover, the present algae are rarely studied for the use of lipid production candidate. A cultivation model similar to the two-stage culture was adopted, which mainly focused on the second stage of lipid accumulation. The aim is to explore the feasibility of ultrasonic as stress condition in improving the lipid accumulation of microalgae during the late growth phase. Through the lab-scale trials an efficient method based on ultrasonic treatment can be drawn out to accelerate lipid production.
Section snippets
Microalgae strain
The microalgae used in this study were A. variabilis purchased from freshwater algae culture collection of the Institute of Hydrobiology in China (FACHB-Collection). The seed strains were cultured initially for 5–7 days in 200-mL Erlenmeyer flasks for activation following by the expanding culture in 1000-mL Erlenmeyer flasks at the temperature of 25 ± 1 °C for 5–7 days. The activated microalgae were centrifuged to form cell pellets which were re-suspended and transferred to the photobioreactors with
Microalgae growth
The microalgae were treated on day 11 by different ultrasonic powers to determine the effects on cells growth, the results of which were shown in Fig. 1. The microalgae under optimal conditions showed low growth activity after the cultivation for 11 days at the condition without ultrasonic (i.e. 0 W). After the ultrasonic treatment on day 11, the microalgae showed an interesting increase with the continued culture time. The maximum biomass concentration of 1.36 g/L was obtained at the ultrasonic
Conclusions
The effects of ultrasonic treatment on microalgae were studied to determine the beneficial aspects induced by ultrasound in the production of biomass and lipid. The results showed increment of biomass concentration on day 12 at the condition of 200 W and 5 min. Interestingly, the lipid content was significantly improved to 46.92% simultaneously under the same conditions leading to a maximum lipid productivity of 54.2 mg/L/d. The ultrasonic treatment indicated no negative effects on the properties
Acknowledgements
This work was gratefully financed by the National Science Fund for Excellent Young Scholars (51322811), Science and Technology Development Planning of Shandong Province (2012GGE27027), the Program for New Century Excellent Talents in University of the Ministry of Education of China (Grant No. NCET-12-0341).
References (34)
- et al.
Bioprospecting for oil producing microalgal strains: evaluation of oil and biomass production for ten microalgal strains
Bioresour. Technol.
(2011) Biodiesel from microalgae
Biotechnol. Adv.
(2007)- et al.
Importance of algae oil as a source of biodiesel
Energy Convers. Manage.
(2011) - et al.
A novel horizontal photobioreactor for high-density cultivation of microalgae
Bioresour. Technol.
(2015) - et al.
Ultrasonic cavitation for disruption of microalgae
Bioresour. Technol.
(2015) - et al.
Optimization and lipid production enhancement of microalgae culture by efficiently changing the conditions along with the growth-state
Energy Convers. Manage.
(2015) - et al.
Review of biodiesel composition, properties, and specifications
Renew. Sustain. Energy Rev.
(2012) - et al.
The effect of phosphate starvation on the lipid and fatty acid composition of the fresh water eustigmatophyte Monodus subterraneus
Phytochemistry
(2006) - et al.
Perspectives of microalgal biofuels as a renewable source of energy
Energy Convers. Manage.
(2014) - et al.
Microalgae for third generation biofuel production, mitigation of greenhouse gas emissions and wastewater treatment: present and future perspectives – a mini review
Energy
(2014)
Nitrogen stress triggered biochemical and morphological changes in the microalgae Scenedesmus sp. CCNM 1077
Bioresour. Technol.
Impact of sonication at 20 kHz on Microcystis aeruginosa, Anabaena circinalis and Chlorella sp
Water Res.
Biodiesel from microalgae: a critical evaluation from laboratory to large scale production
Appl. Energy
Effect of nitrogen and phosphorus starvation on the polyunsaturated triacylglycerol composition, including positional isomer distribution, in the alga Trachydiscus minutus
Phytochemistry
Optimization of mixotrophic cultivation of microalgae Chlorella sp. for biofuel production using response surface methodology
Algal Res.
Evaluation of the potential of 10 microalgal strains for biodiesel production
Bioresour. Technol.
Conversion of microalgae to biofuel
Renew. Sustain. Energy Rev.
Cited by (48)
Effect of ultrasound on Pseudoneochloris marina and Chlorella zofingiensis growth
2023, Bioresource TechnologyEstablishment of ultrasonic stimulation to enhance growth of Haematococcus lacustris
2022, Bioresource TechnologyLow-frequency ultrasound and nitrogen limitation induced enhancement in biomass production and lipid accumulation of Tetradesmus obliquus FACHB-12
2022, Bioresource TechnologyCitation Excerpt :Low-frequency ultrasound is commonly applied to assist in the extraction of substances within biological cells, and studies have found that low-frequency ultrasound could also improve microbial enzyme activity and the permeability of cell membranes (Greenly and Tester, 2015). The low-frequency ultrasound stress was found to promote lipid accumulation in microalgae based on the characteristics of low-frequency ultrasound action (Han et al., 2016). However, studies on promotion of microalgae growth and lipid accumulation by low-frequency ultrasound stress are limited and needs to be further explored.
Enhancement of protein production using synthetic brewery wastewater by Haematococcus pluvialis
2022, Journal of Biotechnology