Chi-Yong Ahn

Comparison of several methods for effective lipid extraction from microalgae

Various methods, including autoclaving, bead-beating, microwaves, sonication, and a 10% NaCl solution, were tested to identify the most effective cell disruption method. The total lipids from Botryococcus sp., Chlorella vulgaris, and Scenedesmus sp. were extracted using a mixture of chloroform and methanol (1:1). The lipid contents from the three species were 5.4-11.9, 7.9-8.1, 10.0-28.6, 6.1-8.8, and 6.8-10.9 g L(-1) when using autoclaving, bead-beating, microwaves, sonication, and a 10% NaCl solution, respectively. Botryococcus sp. showed the highest oleic acid productivity at 5.7 mg L(-1)d(-1) when the cells were disrupted using the microwave oven method. Thus, among the tested methods, the microwave oven method was identified as the most simple, easy, and effective for lipid extraction from microalgae.

Selection of microalgae for lipid production under high levels carbon dioxide

To select microalgae with a high biomass and lipid productivity, Botryococcus braunii, Chlorella vulgaris, and Scenedesmus sp. were cultivated with ambient air containing 10% CO(2) and flue gas. The biomass and lipid productivity for Scenedesmus sp. with 10% CO(2) were 217.50 and 20.65 mg L(-1)d(-1) (9% of biomass), while those for B. braunii were 26.55 and 5.51 mg L(-1)d(-1) (21% of biomass). With flue gas, the lipid productivity for Scenedesmus sp. and B. braunii was increased 1.9-fold (39.44 mg L(-1)d(-1)) and 3.7-fold (20.65 mg L(-1)d(-1)), respectively. Oleic acid, a main component of biodiesel, occupied 55% among the fatty acids in B. braunii. Therefore, the present results suggested that Scenedesmus sp. is appropriate for mitigating CO(2), due to its high biomass productivity and C-fixation ability, whereas B. braunii is appropriate for producing biodiesel, due to its high lipid content and oleic acid proportion.

Harvest of Scenedesmus sp. with bioflocculant and reuse of culture medium for subsequent high-density cultures.

The optimal flocculating conditions for harvesting high-density cultures of Scenedesmus sp. were investigated using inorganic coagulants and the bioflocculant produced by Paenibacillus polymyxa AM49. The flocculated medium as nutrients for subsequent algal cultivation was also tested. Consecutive treatment with 8.5 mM CaCl(2) and 0.2 mM FeCl(3) as coagulants and 1% bioflocculant from the culture broth of P. polymyxa AM49 showed the highest flocculating activity of up to 95% for high density algal cultures. The medium flocculated with the coagulants and bioflocculant showed less than 8% decrease in the growth yield in the subsequent algal cultivation. Furthermore, a 20% or 50% fresh BG11 medium supplement allowed the flocculated medium to maintain a high growth yield in subsequent algal cultivation. These results suggest that the flocculation method presented here is efficient and bio-friendly, and allows the reuse of the flocculated medium, thereby contributing to the economic cultivation and harvest of microalgae.

Rainfall, phycocyanin, and N:P ratios related to cyanobacterial blooms in a Korean large reservoir

Nutrient concentrations and other environmental factors were measured in the Daechung Reservoir for 25 weeks from spring until autumn in 1999. The high irradiance after heavy rainfall provided optimal meteorological conditions for bloom formation during summer, therefore, rain would also appear to forecast imminent bloom. The bloom formation was largely governed by cyanobacteria, in particular, Microcystis spp. and Anabaenaspp. Phycocyanin showed higher correlation with cyanobacteria (r = 0.744, P < 0.001) compared to chlorophyll-a(r = 0.599, P < 0.01). Therefore, phycocyanin was more accurate and useful than chlorophyll-a in quantitatively measuring cyanobacterial blooms. The atomic N:P ratio of the particulate form also showed a high correlation with cyanobacteria (r = 0.541, P < 0.01), increasing from 4.3 to 14.6 during bloom formation, while that of the dissolved form decreased from 25.5 to 8.7. These results indicated that the algae assimilated N significantly without comparable P uptake during the blooming season, which was in sharp contrast to the excessive storage of P during the spring.

Growth inhibition of bloom‐forming cyanobacterium Microcystis aeruginosa by rice straw extract

Aims:  To inhibit the growth of the bloom‐forming cyanobacterium Microcystis aeruginosa using a rice straw extract.

Recent trends in development of biosensors for detection of microcystin.

Increased cyanobacterial blooms, a source of cyanotoxins are linked with climate change and eutrophication in aquatic bodies, a major concern worldwide. Microcystins are potently hepatotoxic, nephrotoxic as well as carcinogenic. Thus microcystins are threat to tourism, agriculture and animals health. However, there is a still lacuna in the knowledge of regulation of microcystins production. Presence of toxic and non-toxic cyanobacterial strains together and occurrence of various microcystin variants in aquatic bodies compounded the problem. Although several analytical techniques for microcystin detection such as bioassay, ELISA, HPLC and LC-MS etc. have been already prevalent, the development of biosensors offered rapid and accurate detection, high reproducibility and portability. Sequencing of Microcystis spp., opened the new vistas towards the development of biosensor at molecular and genetic level. This review incorporates the current trends in the development of biosensors for microcystin detection in the light of state-of-the-art techniques.

Monitoring Approaches for a Toxic Cyanobacterial Bloom

Cyanobacterial blooms, dominated by Microcystis sp. and associated microcystin variants, have been implicated in illnesses of humans and animals. Little is known regarding the formation of blooms and the presence of cyanotoxin variants in water bodies. Furthermore, the role played by ecological parameters, in regulating Microcystis blooms is complicate and diverse. Local authorities responsible for water management are often faced with the challenging task of dealing with cyanobacterial blooms. Therefore, the development of suitable monitoring approaches to characterize cyanobacterial blooms is an important goal. Currently, various biological, biochemical and physicochemical methods/approaches are being used to monitor cyanobacterial blooms and detect microcystins in freshwater bodies. Because these methods can vary as to the information they provide, no single approach seemed to be sufficient to accurately monitor blooms. For example, immunosensors are more suited for monitoring the presence of toxins in clear water bodies while molecular methods are more suited to detect potentially toxic strains. Thus, monitoring approaches should be tailored for specific water bodies using methods based on economic feasibility, speed, sensitivity and field applicability. This review critically evaluates monitoring approaches that are applicable to cyanobacterial blooms, especially those that focus on the presence of Microcystis, in freshwater bodies. Further, they were characterized and ranked according to their cost, speed, sensitivity and selectivity. Suggested improvements were offered as well as future research endeavors to accommodate anticipated environmental changes.

Annual variation of Microcystis genotypes and their potential toxicity in water and sediment from a eutrophic reservoir

The relative genetic diversity of microcystin-producing Microcystis in the water and sediment of the Daechung Reservoir, Korea, was investigated over an entire year, including the cyanobacterial bloom season. The cells of potentially toxic Microcystis strains containing mcyJ genotypes and cells containing the genus-specific cpcBA gene were quantified by a real-time PCR. The ratio of cells with mcyJ genotypes to the total Microcystis population in the water body was the highest (68.3%) in August when the cyanobacterial bloom reached its peak and the microcystin concentration in the water began to increase. A denaturing gradient gel electrophoresis profile analysis of the mcyJ genotypes performed to monitor any changes in the toxic Microcystis population showed the appearance of new genotypes and the disappearance of existing genotypes in the reservoir water collected during the summer months, when compared with the profile for the samples collected in spring and autumn. However, very little change was observed over the course of the year as regards the population diversity of the sediment samples.

Harvesting of Spirulina platensis by cellular flotation and growth stage determination.

Aim:  To investigate an effective harvesting method for Spirulina platensis.

Determination of Cyanobacterial Diversity during Algal Blooms in Daechung Reservoir, Korea, on the Basis of cpcBA Intergenic Spacer Region Analysis

ABSTRACT The detection and prevention of cyanobacterial blooms are important issues in water quality management. As such, the diversity and community dynamics of cyanobacteria during cyanobacterial bloom in the Daechung Reservoir, Korea, were studied by analyzing the intergenic spacer (IGS) region between phycocyanin subunit genes cpcB and cpcA (cpcBA IGS). To amplify the cpcBA IGS from environmental samples, new PCR primers that could cover a wider range of cyanobacteria than previously known primers were designed. In the samples taken around the bloom peak (2 September 2003), seven groups of cpcBA IGS sequences were detected, and none of the amplified cpcBA IGSs was closely related to the cpcBA IGS from chloroplasts. Apart from the Microcystis-, Aphanizomenon (Anabaena)-, Pseudanabaena-, and Planktothrix (Oscillatoria)-like groups, the three other groups of cpcBA IGS sequences were only distantly related to previously reported sequences (<85% similarity to their closest relatives). The most prominent changes during the bloom were the gradual decrease and eventual disappearance of the Aphanizomenon (Anabaena)-like group before the bloom peak and the gradual increase and sudden disappearance of Planktothrix (Oscillatoria)-like groups right after the bloom peak. The community succession profile obtained based on the cpcBA IGS analysis was also supported by a PCR-denaturing gradient gel electrophoresis analysis of the 16S rRNA genes.