The influence of photoperiod and light intensity on the growth and photosynthesis of Dunaliella salina (chlorophyta) CCAP 19/30

The green microalga Dunaliella salina survives in a wide range of salinities via mechanisms involving glycerol synthesis and degradation and is exploited for large amounts of nutraceutical carotenoids produced under stressed conditions. In this study, D. salina CCAP 19/30 was cultured in varying photoperiods and light intensities to study the relationship of light with different growth measurement parameters, with cellular contents of glycerol, starch and carotenoids, and with photosynthesis and respiration. Results show CCAP 19/30 regulated cell volume when growing under light/dark cycles: cell volume increased in the light and decreased in the dark, and these changes corresponded to changes in cellular glycerol content. The decrease in cell volume in the dark was independent of cell division and biological clock and was regulated by the photoperiod of the light/dark cycle. When the light intensity was increased to above 1000 μmol photons m−2 s−1, cells displayed evidence of photodamage. However, these cells also maintained the maximum level of photosynthesis efficiency and respiration possible, and the growth rate increased as light intensity increased. Significantly, the intracellular glycerol content also increased, >2-fold compared to the content in light intensity of 500 μmol photons m−2 s−1, but there was no commensurate increase in the pool size of carotenoids. These data suggest that in CCAP 19/30 glycerol stabilized the photosynthetic apparatus for maximum performance in high light intensities, a role normally attributed to carotenoids

The Selectivity of Milking of Dunaliella salina

The process of the simultaneous production and extraction of carotenoids, milking, of Dunaliella salina was studied. We would like to know the selectivity of this process. Could all the carotenoids produced be extracted? And would it be possible to vary the profile of the produced carotenoids and, consequently, influence the type of carotenoids extracted? By using three different D. salina strains and three different stress conditions, we varied the profiles of the carotenoids produced. Between Dunaliella bardawil and D. salina 19/18, no remarkable differences were seen in the extraction profiles, although D. salina 19/18 seemed to be better extractable. D. salina 19/25 was not “milkable” at all. The milking process could only be called selective for secondary carotenoids in case gentle mixing was used. In aerated flat-panel photobioreactors, extraction was much better, but selectiveness decreased and also chlorophyll and primary carotenoids were extracted. This was possibly related to cell damage due to shear stress

Divergent Evolution of CHD3 Proteins Resulted in MOM1 Refining Epigenetic Control in Vascular Plants

Arabidopsis MOM1 is required for the heritable maintenance of transcriptional gene silencing (TGS). Unlike many other silencing factors, depletion of MOM1 evokes transcription at selected loci without major changes in DNA methylation or histone modification. These loci retain unusual, bivalent chromatin properties, intermediate to both euchromatin and heterochromatin. The structure of MOM1 previously suggested an integral nuclear membrane protein with chromatin-remodeling and actin-binding activities. Unexpected results presented here challenge these presumed MOM1 activities and demonstrate that less than 13% of MOM1 sequence is necessary and sufficient for TGS maintenance. This active sequence encompasses a novel Conserved MOM1 Motif 2 (CMM2). The high conservation suggests that CMM2 has been the subject of strong evolutionary pressure. The replacement of Arabidopsis CMM2 by a poplar motif reveals its functional conservation. Interspecies comparison suggests that MOM1 proteins emerged at the origin of vascular plants through neo-functionalization of the ubiquitous eukaryotic CHD3 chromatin remodeling factors. Interestingly, despite the divergent evolution of CHD3 and MOM1, we observed functional cooperation in epigenetic control involving unrelated protein motifs and thus probably diverse mechanisms

Stress-Induced Activation of Heterochromatic Transcription

Constitutive heterochromatin comprising the centromeric and telomeric parts of chromosomes includes DNA marked by high levels of methylation associated with histones modified by repressive marks. These epigenetic modifications silence transcription and ensure stable inheritance of this inert state. Although environmental cues can alter epigenetic marks and lead to modulation of the transcription of genes located in euchromatic parts of the chromosomes, there is no evidence that external stimuli can globally destabilize silencing of constitutive heterochromatin. We have found that heterochromatin-associated silencing in Arabidopsis plants subjected to a particular temperature regime is released in a genome-wide manner. This occurs without alteration of repressive epigenetic modifications and does not involve common epigenetic mechanisms. Such induced release of silencing is mostly transient, and rapid restoration of the silent state occurs without the involvement of factors known to be required for silencing initiation. Thus, our results reveal new regulatory aspects of transcriptional repression in constitutive heterochromatin and open up possibilities to identify the molecular mechanisms involved

Silencing: new faces of Morpheus' molecule

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102123/1/embj2009388.pd

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

Carotenogenesis in Nannochloropsis oculata under oxidative and salinity stress

Nannochloropsis oculata is a unicellular microalgae which is vastly found throughout the environment and have been widely studied due to its high productivity of secondary metabolites and oil content. It is majorly cultured in the aquaculture sector as fish feed and for industries for its polyunsaturated fatty acids. This work aims to study the impact of salinity and oxidative stress on the expression of carotenoid biosynthesis genes and the accumulation of their products in N. oculata via qPCR and HPLC analyses. Three genes responsible for production of high value carotenoids namely lycopene beta-cyclase (CrTL-B/LCYB), beta-carotene oxygenase (CrTO) and beta-carotene hydroxylase (CrTR) under different stresses and time points were identified and quantified, and the amount of their products namely β-carotene, zeaxanthin, canthaxanthin, and astaxanthin was measured. N. oculata was treated with different concentrations of Cu2+ ion (1, 2, and 5 ppm) and NaCl (50, 150, 250 mM) which resembles conditions of oxidative and salinity stress, respectively. RNA and carotenoids extraction, RT-PCR, qPCR and HPLC was carried out in order to identify the correlation of carotenogenesis genes expression with carotenoids production. Under exposure of both treatments, the carotenoids biosynthesis genes were upregulated up to 6-fold compared to control and targeted carotenoids were overexpressed up to 7-fold. Results from this study gave insights which are beneficial in understanding microalgae’s responses towards abiotic stress via the synthesis of carotenoids

Carotenogenesis in Nannochloropsis oculata under oxidative and salinity stress

Nannochloropsis oculata is a unicellular microalgae which is vastly found throughout the environment and have been widely studied due to its high productivity of secondary metabolites and oil content. It is majorly cultured in the aquaculture sector as fish feed and for industries for its polyunsaturated fatty acids. This work aims to study the impact of salinity and oxidative stress on the expression of carotenoid biosynthesis genes and the accumulation of their products in N. oculata via qPCR and HPLC analyses. Three genes responsible for production of high value carotenoids namely lycopene beta-cyclase (CrTL-B/LCYB), beta-carotene oxygenase (CrTO) and beta-carotene hydroxylase (CrTR) under different stresses and time points were identified and quantified, and the amount of their products namely β-carotene, zeaxanthin, canthaxanthin, and astaxanthin was measured. N. oculata was treated with different concentrations of Cu2+ ion (1, 2, and 5 ppm) and NaCl (50, 150, 250 mM) which resembles conditions of oxidative and salinity stress, respectively. RNA and carotenoids extraction, RT-PCR, qPCR and HPLC was carried out in order to identify the correlation of carotenogenesis genes expression with carotenoids production. Under exposure of both treatments, the carotenoids biosynthesis genes were upregulated up to 6-fold compared to control and targeted carotenoids were overexpressed up to 7-fold. Results from this study gave insights which are beneficial in understanding microalgae’s responses towards abiotic stress via the synthesis of carotenoids

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