Cocconeis neothumensis, a benthic diatom living as epiphyte on Posidonia oceanica leaves, was hypothesised to synthesize secondary metabolites inducing apoptosis in the androgenic gland of the protandric shrimp Hippolyte inermis. The optimization of C. neothumensis cultures is a primary aim in order to identify and characterise the active compounds produced by this diatom. Light intensity and concentration of nutrients, such as silicates and selenium, are of major importance in determining the growth rate of diatoms and the maximum produced biomass. Thus, we evaluated the growth performances of C. neothumensis cultures at different light intensities, corresponding to those recorded in Posidonia oceanica meadows in April, when the induction of sexual reversal in Hippolyte inermis occurs; the growth performances were also determined in relation to different selenium and silicate availability in the culture medium and the possible interactions between these two micronutrients were evaluated. Two methods of cultivations were compared: batch cultures in Petri dishes and cultures in a bioreactor with a continuous medium flow in the system. C. neothumensis showed a faster growth at low light intensities, although with a good acclimation capacity in the range from 60 to 140 μmol photons m−2 s −1 . The presence of selenium in the medium improved both the exponential growth rate and the maximum cell density. The same results were evidenced for a silicate concentration double that in Guillard f/2 medium. On the other hand, a simultaneous increase of silicate concentration and the presence of selenium led to a loss of the positive effects detected with single nutrients. This result suggests either a possible antagonism in selenium and silicate uptake or a negative interaction between these two micronutrients in Cocconeis. The yields of the two tested cultivation methods calculated in terms of diethyl ether extract dry weight per unit of substrate area were highest for the bioreactor.

This work was fully funded by the E.U. in the frame of the E.U. project PHARMAPOX (NEST STREP Adventure 4800).

9 páginas, 5 figuras, 1 tabla

Peer reviewed