Eichi Manabe

CO2 removal by high-density culture of a marine cyanobacterium synechococcus sp. using an improved photobioreactor employing light-diffusing optical fibers

A light diffusing optical fiber (LDOF) photobioreactor with an improved gas input system has been used for the high-density culture of a marine cyanobacterium Synechococcus sp. Optimum conditions for CO2 removal and biomass production were investigated. Maximum CO2 removal of 4.44 g/L/d was achieved using an initial cell concentration of 6.8 g/L. The biomass yield was 0.97 g/L for a 12-culture time. Continuous cultures, in which medium was filtered using a ceramic membrane module, showed enhanced growth, with a final cell concentration of 11.2 g/L. These results demonstrate the potential of LDOF photobioreactor units for CO2 removal and biomass production using marine cyanobacteria.

Influence of ammonium chloride on growth and fatty acid production by Spirulina platensis

Changes in growth and fatty acid content ofSpirulina platensis were examined after transferring cells into media containing various concentrations of ammonium chloride. Photosynthetic O2 evolution rate decreased with increasing ammonium chloride concentration. Therefore, the algal growth was interrupted by ammonium chloride addition. On the other hand, total fatty acid content markedly increased after addition of ammonium chloride to a concentration of 15–50 mM and was maximized 40–48 h after addition of 25 mM ammonium chloride. The increases in palmitic and oleic acid content were especially remarkable. However, this began to decrease 48 h after the addition of 25 mM of ammonium chloride. Also, γ-linolenic acid content increased continuously during a 72-h incubation. As a result,Spirulina platensis cells containing about 2% γ-linolenic acid were obtained by ammonium chloride treatment, representing an increase of 1.5–2-fold compared to untreated cells.

Development of a rapid isolation procedure for coccolith ultrafine particles produced by coccolithophorid algae

A rapid procedure for effective purification of large quantities of coccolith ultrafine particles from marine algae is reported. Coccoliths are detached from cells by optimized sonication in the presence of 50 mM NaHCO3. Contaminating cell debris is then removed from coccoliths by cycles of washing and floatation. Coccolith particles were purified fromEmiliania huxleyi andPleurochrysis carterae. The surface area of these particles is three to five times greater than synthetic calcite particles. Glucose oxidase and uricase have been immobilized onto purified coccolith ultrafine particles to illustrate their potential as a support material for biotechnological application.

Production of ultrafine calcite particles by coccolithophorid algae grown in a biosolar reactor supplied with sunlight

Ultrafine calcite particle production by coccolithophorid algae using a biosolar reactor system was carried out. Solar light was collected by Fresnel lenses and transmitted to a bundle of light diffusing optical fibers (LDOFs) that distributed light through the algal culture. The irradiance spectrum of light emitted from the LDOF surface was the same as that of solar light.Emiliania huxleyi was cultured for 8 d, and 43 mg/L of calcite were produced. These results demonstrate the potential of the biosolar reactor system for CO2 fixation, and ultrafine calcite particle production using coccolithophorid algae and sunlight.

Increased coccolith production by Emiliania huxleyi cultures enriched with dissolved inorganic carbon

Cells of Emiliania huxleyi grown on Eppleys medium enriched with dissolved inorganic carbon (DIC) developed multiple layers of coccoliths. The maximum diameter of cells grown in the presence of 13.2 mM DIC was 12.3 μm, whereas that of cells grown in the presence of 1.5 mM DIC was 8.0 μm. Although enrichment of Eppleys medium with DIC increased both coccolith production and cell growth, coccolith production was enhanced to a greater extent than cell growth. The enrichment of Eppleys medium with DIC was used to enhance production of coccolith particles by E. huxleyi. Repeated-batch culture, in which DIC, Ca2+, nitrate and phosphate concentrations in the medium were maintained by replacing the culture medium, was carried out in a closed photobioreactor. During repeated-batch culture, a maximum coccolith yield of 560 mg/l for 2 days and a maximum biomass yield of 810 mg/l for 2 days were achieved. Enrichment and maintenance of DIC is therefore an efficient method for the production of large quantities of coccoliths.

Continuous production of extracellular ultrafine calcite particles by the marine coccolithophorid alga Pleurochrysis carterae

A new procedure for the production of ultrafine calcite particles by the marine coccolithophorid alga Pleurochrysis carterae is reported. During continuous culture, calcite particles (coccoliths) were detached from the cell surface by optimized air-bubbling, which greatly reduced the damage associated with previous sonication methods. Detached calcite particles could be continuously recovered directly from the culture medium using a nylon mesh membrane filtration module. Cells remained viable and continued to produce coccoliths during culture. The optimum productivity of ultrafine calcite particles was 18 mg/l per day. These results demonstrate the potential for a continuous system for the photosynthetically driven removal of CO2 and its fixation into ultrafine inorganic calcite particles.