Cultured microalgae

Autotrophic and heterotrophic microalgae have different growth reqnirements. Autotrophic microalgae have an absolute requirement for light for photosynthesis and may 

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DUERR E o, MOLNAR A and SATO V (1998) Cultured microalgae as aquaculture feeds. Journal of Marine Biotechnology, 6,65-70. 

A. Richmond, CRC Handbook of Microalgae Mass Culture, CRC Press, Boca Raton, Fla., 1986. 

The microalgae are cultured in bioreactors under solar or artiflcial light in the presence of carbon dioxide and salts. The bioreactors may be closed systems made of polyethylene sleeves rather than open pools. Optimal conditions for pigment production are low to medium light intensity and medium temperatures (20 to 30°C). Pigment extraction is achieved by cell breakage, extraction into water or buffered solution, and centrifugation to separate out the filtrate. The filtrate may then be partly purified and sterilized by microfiltration and spray dried or lyophilized. 

Other kinds of bloassays have been used to detect the presence of specific allelochemical effects (8), effects on N2 fIxatlon (9), the presence of volatile compounds (10) and of Inhibitory substances produced by marine microalgae (11). Putnam and Duke (12) have summarized the extraction techniques and bioassay methods used In allelopathy research. Recent developments In high performance liquid chromatography (HPLC) separation of allelochemlcals from plant extracts dictates the need for bloassays with sensitivity to low concentrations of compounds contained In small volumes of eluent. Einhellig at al. (13) described a bloassay using Lemna minor L. growing In tissue culture cluster dish wells that maximizes sensitivity and minimizes sample requirements. 

Figure 17. Microalgae culture in open system (raceway) and close photobioreactor (Almeria University and Palmerillas Research Center).

The occurrence of toxic compounds in plant tissues is not necessarily related to allelopathy. Allelopathy should be evidenced through experiments in which a toxic product is shown to be released from the putative aggressor, and arrives at the putative victim in functional concentrations under reasonably natural conditions (Inderjit and Callaway 2003). First of all, laboratory experiments dealing with allelopathy should demonstrate the release of a compound in the medium. Two methods to collect allelchemicals released by laboratory cultures of macrophyte or microalgae are described in Sections 5 and 6. 

With advances in methods of isolation and cultivation of microalgae and cyanobacteria, and the striking bioactivity of other microbial metabolites, research into the chemistry of culturable algae has escalated since the 1990s. Metabolites from these... 

Photobioreactors Light-controlled chambers used to grow microalgae in mass culture. 

Photosynthetic microalga Haematococcus pluvicdis) vfikS inoculated at 2.0 kg dry cell rn and cultured in a basal medium (containing yeast extract, acetate, asparagine, and some metals) under illumination by fluorescent lamps. The cell concentrations are shown in Table P4.4. 

The size of the glass beads is important. The optimal size for bacteria and spores is 0.1 mm it is 0.5 mm for yeast, mycelia, microalgae, and unicellular animal cells such as leucocytes or tissue culture cells. The speed of disruption... 

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