Characterization And Photoprotection Mechanisms Of A Strain Of Nannochloropsis Sp.

Nannochloropsis is a genus of algae within the heterokont line of eukaryotes, which has been shown to contain species that can be used to produce biofuel and pigments. However, species of Nannochloropsis (Eustigmatophyceae) possess very small cells of simple morphology that are difficult to identify by morphological or ultrastructural characteristics and are easily confused with green microalgae due to their yellow-green color. This study presents a detailed documentation of marine Nannochloropsis and a formal description of a strain of Nannochloropsis, formerly thought to be a species of Chorella. The morphology, ultrastructure, pigment composition and fatty acid content have been characterized and multi-gene phylogenetic analysis of this alga was undertaken. The morphological and molecular results supported the hypothesis that Nannochloropsis sp. QD001investigated in this study belongs to the genus Nannochloropsis in the Eustigmatophyceae and suggested that the Nannochloropsis sp. is probably "Nannochloropsis maritimd". Furthermore, pigment composition and fatty acid content analysis results indicated that members of the genus Nannochloropsis are a promising source of valuable pigments and biofuel.Non-photochemical quenching (NPQ) of chlorophyll fluorescence is thought to be an indicator of an essential regulation and photoprotection mechanism against high-light stress in photosynthetic organisms, and is associated with an enzymatic xanthophyll cycle (XC) which is controlled by the light-driven transthylakoid proton gradient (â–³pH). The mechanisms of NPQ vary among different photosynthetic organisms, In Nannochloropsis sp., the mechanism of NPQ which regulates photosynthesis during light fluctuations has not been reported, In this report, special illumination conditions and chemicals were used to perturb the kinetics of the ApH build-up, of the xanthophyll cycle and of NPQ. We found that NPQ in Nannochloropsis sp. was stimulated rapidly on exposure to actinic light (in tens of seconds) and relaxated fast in dark. NPQ was completely restrained in the absence of ApH, which indicated that the ApH could be obligatory for NPQ. The xanthophylls are also essential for NPQ, but it is lack of Lutein and strictly mediated by the ApH. NPQ in Nannochloropsis sp. was suppressed under high light conditions with DCCD, indicating that in Nannochloropsis sp. there was a protonable LHCSR-like protein acting as a sensor of lumen pH. The results demonstrated that the mechanism of NPQ in Nannochloropsis sp. resembles that of diatoms.Quantitative real-time reverse transcription PCR (RT-qPCR), a sensitive technique for quantifying gene expression, depends on the stability of the reference gene(s) used for data normalization. To date, few studies on reference genes have been undertaken for Nannochloropsis sp. In this study,12potential reference genes were evaluated for their expression stability using the geNorm and NormFinder statistical algorithms by RT-qPCR. The results showed that the best reference genes differed with the treatments: different light intensities (DL), the diurnal cycle (DC), high light intensity (HL) and low temperature treatments (LT). A combination of ACT1, ACT2and TUA would be appropriate as a reference panel for normalizing gene expression data across all the treatments. ACT2showed the most stable expression across all tested samples but was not the most stable one for individual treatments. Though18S showed the least stable expression considering all tested samples, it is the most stable one for LT using geNorm. The expression of Lhc confirmed that the appropriate reference genes are crucial. These results provide a foundation for more accurate use of RT-qPCR under different experimental conditions in Nannochloropsis sp. gene analysis.