Effect of sodium chloride on growth and lipid accumulation of Chlorella protothecoides CS-41 / 生物工程学报

With basal medium, we studied the growth status, lipid droplet distribution, total lipid content of Chlorella protothecoides CS-41 treated with different concentrations of sodium chloride (0, 150, 300 and 600 mmol/L) by optical microscopy, electron microscopy, confocal laser focusing and Nile red staining. Results show that the addition of NaCl affected the growth of Chlorella protothecoides CS-41. With the increase of NaCl concentration, the growth rate of Chlorella was inhibited. Chlorella cell wall became thicker, and lipid droplets increased. At the early stage, the amount of lipid droplets in the 600 mmol/L NaCl culture was the highest, but at the late-log stage, the amount of lipid droplets increased with the increase of the biomass of culture in 150 and 300 mmol/L NaCl culture. At the stable stage, biomass (dry weight) in 300 mmol/L NaCl culture was 73.55% of that in the control, but the total lipid content was 2.22 times higher than that in the control. A certain concentration of sodium chloride treatment can significantly increase the lipid content of Chlorella protothecoides CS-41.

Heat shock response of Chlorella protothecoides during greening.

Heterotrophically grown cells of Chlorella protothecoides were transferred to autotrophic medium and allowed to green at 25°C. The protein synthetic activity of the greening cells measured in terms of incorporation of [35S]-methionine showed a maximum around 20 h of greening and thereafter started declining. Similarly, an analysis of densitometric tracings of the fluorographic profile of the polypeptides associated with both total cellular fraction and membrane fractions during different hours of greening revealed that maximum number of polypeptides were getting labelled around 20 h of greening. At 20 h of greening, the cells were shifted to 40°C and the effect of heat shock on protein synthesis was studied. The heat shock treatment caused a definite decrease in the incorporation of [35S]- methionine into proteins. Due to heat shock, the synthesis of total soluble proteins was affected much more than that of the thylakoid membrane bound proteins. When the cells were transferred back to 25°C after a brief period of heat shock at 40°C, there was a considerable recovery in the protein synthesis and this recovery was found to be significant in the case of soluble proteins, while there was no such definite recovery in the synthesis of thylakoid membrane bound proteins.

Immediate effects of pyridazinone herbicides on photosynthetic electron transport in algal systems.

Pyridazinone herbicides, SANDOZ 9785 (4-chloro-5-dimethylamino2-phenyl- 3-(2H) pyridazinone), SANDOZ 9789 (4-chloro-5 (methylamino)-2-(α, α, α-trifluoro-m-tolyl- 3-(2H) pyridazinone) and SANDOZ 6706 (4-chloro-5-(methylamino)-2-(α, α, α-trifluoro-mtolyl- 3-(2H) pyridazinone) inhibited photosystem II electron transport in Chlorella protothecoides, when the herbicides were added to the assay medium. The inhibitory eficiency varied with the algal species and the nature of substitution of pyridazinones. Using 3 algal systems viz., Chlorella, Scenedesmus and Anacystis, the I50 value of for the inhibition of photosynthesis of 3 substituted pyridazinones (SANDOZ 9785, SANDOZ 6706 and SANDOZ 9789) were determined. SANDOZ 9789 was found to be the weakest inhibitor of photosystem II electron transport (H2Ο→ benzoquinone) as compared to SANDOZ 9785 and SANDOZ 6706. In general, the order of inhibition could be given as SANDOZ 6706 > SANDOZ 9785 > SANDOZ 9789. The I50 value of photosynthetic particles obtained from Chlorella cells was similar to that of whole cells, suggesting that the cell wall of Chlorella did not act as a barrier for the herbicide action. Studies on the light intensity dependence of SANDOZ 9785 inhibition of electron transport (H2O→ benzoquinone) showed that the light-dependent portion of the curve was more sensitive than the light independent portion of the curve. It is suggested that the site of action was on the reducing side of photosystem II.

Correlation between inhibition of photosynthesis and growth of Chlorella treated with methyl parathion.

When methyl parathion (Ο,Ο dimethyl O p nitrophenyl phosphorothioate), an organophosphorous insecticide, was added to an exponentially growing culture of Chlorella protothecoides and the effects were followed for 12 days, the following observations were made: a) In autotrophic culture the cell number and the chlorophyll content decreased as compared to the control. These changes paralleled the inhibition of the rate of net photosynthesis, suggesting that the photosynthetic apparatus was the primary target of the insecticide action. b) The inhibition of cell growth (on cell number basis) also occurred in the case of heterotrophic culture at 100 μΜ insecticide concentration but the inhibition was less as compared to that of an autotrophic culture. c) The cell diameter in treated culture increased by 10 20% in both autotrophic and heterotrophic cultures. The observations, (b) and (c) suggest that apart from the photosynthetic apparatus, the insecticide has other sites of action, but the sensitivity of these sites to the insecticide is less than that of the photosynthetic apparatus.