A new photobioreactor for continuous marennin production with a marine diatom: influence of the light intensity and the immobilised-cell matrix (alginate beads or agar layer)

T. Lebeau, P. Gaudin, R. Moan, J.-M. Robert-2002

Applied Microbiology and Biotechnology, 59(2-3): 153-159

Abstract:

In oyster ponds, the marine diatom Haslea ostrearia synthesises and excretes a hydrosoluble pigment of commercial interest called marennin. During the benthic stage, when algal cells are naturally immobilised in their own polysaccharides, marennin production is higher. To optimise this production, axenic cultures of H. ostrearia were immobilised in a polysaccharidic matrix (alginate or agar) and introduced into a new photobioreactor device for continuous marennin production. Solute diffusion was improved using an alginate beads monolayer, leading to higher levels of cell growth (a 2-fold higher cell concentration) and marennin productivity (7.57-8.80 mg day^-1 l^-1). An increase in the light intensity (from 3.0 to 8.5x10¹⁶ quanta cm^-2 s^-1) led to an earlier and 1.3-fold higher production of marennin. However, the higher light intensity led to a higher rate of cell death [0.29 instead of 0.40 ng chlorophyll a (10⁶ cells)^-1]. Due to the secondary nature of marennin metabolism, it would be necessary to alternate between culture conditions favouring cell growth (moderate light intensity and no limiting nitrate supply) and those promoting marennin production (high light intensity and limiting nitrate supply).

(Laboratoire de Biologie Marine, Institut des Substances et des Organismes de la Mer (ISOmer), Université de Nantes, 2, rue de la Houssinière, BP 92208, 44322 Nantes cedex 3, France, e-mail : t.lebeau@uha.fr)

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