β-carotene Production of UV-C Induced Dunaliella salina Under Salt Stress

Dunaliella salina is an important microalga for β-carotene production. In Thailand, the D. salina has not been commercially cultivated. Aim of this study was to screen high β-carotene producing mutants. D. salina KU11 cells were radiated with 0.4 mmol photons m-2·s-1 UV-C for 22 min. After 3 weeks, colonies which survived after radiation were allowed to grow on agar plates; fifty colonies out of 19,720 UV-mutagenized strains turned to orange. These colonies were picked up and transfer to modified Johnson medium. Four mutants out of fifty were KU5, KU18, KU20 and KU37 significantly produced high β-carotene at the stationary phase approximately up to 1.62, 2.03, 1.32 and 1.21 folds, respectively, compared to the wild type strain. In all three consecutive cycles of cultivation, the mutant KU18 accumulated 2.4-8.5 folds β-carotene (µg/ml) and 2.1-4.8 folds β-carotene (pg/cell) higher than the wild type, whereas cell density of the mutant KU18 was not different from the wild type. This is the new record of b-carotene producing mutant isolated from saline soil in Thailand

Stimulation of Hydrogen Photoproduction in Chlorella sorokiniana Subjected to Simultaneous Nitrogen Limitation and Sulfur- and/or Phosphorus-Deprivation

Photosynthetic hydrogen (H2 ) production by green algae has fascinated biologists and energy experts, due to the potential application of this process for renewable energy. In this study, H2 photoproduction and PSII photochemical activities were investigated in Chlorella sorokiniana exposed to simultaneous nitrogen limitation and sulfur (S-) and/ or phosphorus (P-) deprivation. Under S-deprivation, C. sorokiniana produced about 48.2 mL L-1 of H2 . Moreover, simultaneous nitrogen limitation (0.7 mM NH4 Cl) and sulfur- and/or phosphorus-deprivation significantly increased H2 production of C. sorokiniana over that of S-deprivation alone. Maximum H2 outputs of 77.3, 98.1 and 125.1 mL L-1 were obtained in the N-limited cultures exposed to P-deprivation (TAP-P), S-deprivation (TAP-S) and simultaneous S- and P-deprivation (TAP-S-P), respectively. The average rate of H2 production for the N-limited culture exposed to TAP-P, TAP-S and TAP-S-P was 1.07, 1.36 and 1.50 mL L-1 h-1, respectively. Interestingly, the H2 inducement time in the culture subjected to simultaneous N-limitation and S- and/or P-deprivation was much shorter than that of traditional S-deprivation. The photosynthetic inhibitors, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropylp-benzoquinone (DBMIB) repressed H2 production in TAP-S-P (0.7 mM NH4 Cl) medium by 68.04% and 98.65%, respectively. The conditions of simultaneous N-limitation, S- and P-deprivation provided another efficient method for inducing H2 production in C. sorokiniana. In addition, we also found that two-thirds of the required electrons were generated from the splitting of H2 O in PSII and that the remaining onethird possibly came from some other substrate catabolism