Tolga Göksan

Effects of light path lengths and initial culture density on the cultivation of Chaetoceros muelleri (Lemmermann, 1898)

Abstract In the cultivation of a marine diatom Chaetoceros muelleri (Lemmermann, 1898), flat plate vertical glass reactors with light path lengths of 1 or 3 cm were used in the laboratory under a constant photon flux density (PFD) of 190 μmol photon m −2 s −1 . In the first experiment, equal inocula were added in the two bioreactors (1 and 3 cm light path); by the end of the second day, cell concentration was low in the 1-cm light path bioreactor, possibly indicating photoinhibition, since growth of the culture increased in the 3-cm light path bioreactor. As for in the second trial, the areal volumes were equal, that is, the cell concentration was increased three-fold in 1 cm light path to equalize the areal optic densities in both reactors. After the harvest started, average of the volumetric output rates in 1 cm ( P V1 cm ) and 3 cm light paths ( P V3 cm ) were calculated to be 0.22 and 0.10 g l −1 day −1 , and areal output rates in 1 cm ( P A1 cm ) and 3 cm ( P A3 cm ) light paths were calculated to be 1.80 and 2.53 g m −2 day −1 , respectively. The optimal population density was obtained by a daily harvest of 5% of culture volume to be 2.39 g m −2 day −1 in 1 cm light path and 3.27 g m −2 day −1 in 3 cm light path. Light path length of 3 cm was found optimal in both with low and high initial cell densities.

Photon irradiance required to support optimal growth and interrelations between irradiance and pigment composition in the green alga Haematococcus pluvialis

The aim of the work was to find the optimal photon irradiance for the growth of green cells of Haematococcus pluvialis and to study the interrelations between changes in photochemical parameters and pigment composition in cells exposed to photon irradiances between 50 and 600 µmol m−2 s−1 and a light:dark cycle of 12:12 h. Productivity of cultures increased with irradiance. However, the rate of increase was higher in the range 50–200 µmol −2 s−1. The carotenoid content increased with increasing irradiance, while the chlorophyll content decreased. The maximum quantum yield of PSII (Fv/Fm) gradually declined from 0.76 at the lowest irradiance of 50 µmol −2 s−1 to 0.66 at 600 µmol −2 s−1. Photosynthetic activity showed a drop at the end of the light period, but recovered fully during the following dark phase. A steep increase in non-photochemical quenching was observed when cultures were grown at irradiances above 200 µmol −2 s−1. A sharp increase in the content of secondary carotenoids also occurred above 200 µmol m−2 s−1. According to our results, with H. pluvialis green cells grown in a 5-cm light path device, 200 µmol −2 s−1 was optimal for growth, and represented a threshold above which important changes in both photochemical parameters and pigment composition occurred.