Expression of fatty acid desaturase genes and fatty acid accumulation in Chlamydomonas sp. ICE-L under salt stress

Physiological effects of sulfadiazine and sulfamethoxazole on Skeletonema costatum and toxicological evaluation using IBRv2 index

Sulfonamide antibiotics, widely used in human and veterinary medicine as well as agriculture, pose environmental concerns due to their stability and poor biodegradability. This study fills a critical gap in understanding the ecological impact of sulfonamide antibiotics on marine microalgae, particularly Skeletonema costatum, a key primary producer in marine ecosystems. This study investigated the biological responses of the marine microalga Skeletonema costatum to sulfadiazine (SD) and sulfamethoxazole (SMX). Both antibiotics significantly impacted S. costatum, with SD having a more pronounced effect. Growth studies showed a clear dose-response relationship: Low concentrations (0.5 mg/L) of SD and SMX stimulated growth, while higher concentrations (3 mg/L, 5 mg/L, and 10 mg/L) inhibited growth. The 96-hour half-maximal inhibitory concentrations (96h-IC50) were 1.654 mg/L and 1.838 mg/L, respectively, initially indicating that SD has a stronger inhibitory effect on S. costatum than SMX. Photosynthetic activity, measured by chlorophyll a content and the maximum quantum yield of photosystem II (Fv/Fm) values, showed that low concentrations (0.5 mg/L) of SD and SMX increased photosynthetic efficiency, while high concentrations (3 mg/L, 5 mg/L, and 10 mg/L) significantly inhibited it. Antioxidants activity analysis revealed that SD and SMX exposure altered superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and malondialdehyde (MDA) levels. SOD, GR, and GSH-Px levels initially increased but later decreased, suggesting a synergistic effect, while MDA levels consistently increased, indicating oxidative stress and biochemical disruption in algal cells. The Integrated Biomarker Response Version 2 (IBRv2) index provided a comprehensive evaluation of the ecological risks posed by SD and SMX, demonstrating that these antibiotics can significantly disrupt the physiology of marine microalgae. The IBRv2 index provided a comprehensive evaluation of the ecological risks posed by SD and SMX, demonstrating that these antibiotics can significantly disrupt the physiology of marine microalgae. Higher IBRv2 values for SD exposure indicated more substantial impacts on S. costatum. This study underscores the significant ecological risks of sulfonamide antibiotics in marine environments, highlighting the need for further research and regulation to mitigate their impact.

Genomics and transcriptomics reveal β-carotene synthesis mechanism in Dunaliella salina

Dunaliella salina is by far the most salt-tolerant organism and contains many active substances, including β-carotene, glycerol, proteins, and vitamins, using in the production of dried biomass or cell extracts for the biofuels, pharmaceutical formulations, food additives, and fine chemicals, especially β-carotene. We report a high-quality genome sequence of D. Salina FACHB435, which has a 472 Mb genome size, with a contig N50 of 458 Kb. A total of 30,752 protein-coding genes were predicted. The annotation results evaluated by BUSCO was shown that completeness was 91.0% and replication was 53.1%. The fragments were 6.3% and the deletions were 2.6%. Phylogenomic and comparative genomic analyses revealed that A. thaliana diverged from Volvocales about 448 million years ago, then Volvocales C. eustigma, D. salina, and other species diverged about 250 million years ago. High light could promote the accumulation of β-carotene in D. salina at a 13 d stage of culture. The enrichment of DEGs in KEGG, it notes that the predicted up-regulated genes of carotenoid metabolic pathway include DsCrtB, DsPDS, DsZ-ISO, DsZDS, DsCRTISO, DsLUT5, DsCrtL-B, and DsCCD8, while the predicted down-regulated genes include DsCrtF, and DsLUT1. The four genes that were both up-regulated and down-regulated were DsZEP, DsCrtR-b, DsCruA/P and DsCrtZ 4. The research results can provide scientific basis for the industrialization practice of D. salina.

Microbial metabolomic responses to changes in temperature and salinity along the western Antarctic Peninsula

Seasonal cycles within the marginal ice zones in polar regions include large shifts in temperature and salinity that strongly influence microbial abundance and physiology. However, the combined effects of concurrent temperature and salinity change on microbial community structure and biochemical composition during transitions between seawater and sea ice are not well understood. Coastal marine communities along the western Antarctic Peninsula were sampled and surface seawater was incubated at combinations of temperature and salinity mimicking the formation (cold, salty) and melting (warm, fresh) of sea ice to evaluate how these factors may shape community composition and particulate metabolite pools during seasonal transitions. Bacterial and algal community structures were tightly coupled to each other and distinct across sea-ice, seawater, and sea-ice-meltwater field samples, with unique metabolite profiles in each habitat. During short-term (approximately 10-day) incubations of seawater microbial communities under different temperature and salinity conditions, community compositions changed minimally while metabolite pools shifted greatly, strongly accumulating compatible solutes like proline and glycine betaine under cold and salty conditions. Lower salinities reduced total metabolite concentrations in particulate matter, which may indicate a release of metabolites into the labile dissolved organic matter pool. Low salinity also increased acylcarnitine concentrations in particulate matter, suggesting a potential for fatty acid degradation and reduced nutritional value at the base of the food web during freshening. Our findings have consequences for food web dynamics, microbial interactions, and carbon cycling as polar regions undergo rapid climate change.

Pollutants removal, microbial community shift and oleic acid production in symbiotic microalgae-bacteria system

The functional interaction between microorganisms is key in symbiotic microalga-bacteria systems; however, evaluations of fungi and pathogenic microorganisms are not clear. In this study, the roles of three groups (i.e., microalgae-activated sludge (MAS), Microalgae, and activated sludge) in pollutant removal and biomass recovery were comparatively studied. The data implied that microalgal assimilation and bacterial heterotrophic degradation were the major approaches for degradation of nutrients and organic matter, respectively. According to 16S rRNA and internal transcribed spacer sequencing, the relative abundance of Rhodotorula increased remarkably, favoring nutrient exchange between the microalgae and bacteria. The abundances of two types of pathogenic genes (human pathogens and animal parasites) were reduced in the MAS system. The oleic acid content in the MAS system (51.2 mg/g) was 1.7 times higher than that in the Microalgae system. The results can provide a basis for practical application and resource utilization of symbiotic microalgae-bacteria systems.

Photosynthetic adaptation to polar life: Energy balance, photoprotection and genetic redundancy

The persistent low temperature that characterize polar habitats combined with the requirement for light for all photoautotrophs creates a conundrum. The absorption of too much light at low temperature can cause an energy imbalance that decreases photosynthetic performance that has a negative impact on growth and can affect long-term survival. The goal of this review is to survey the mechanism(s) by which polar photoautotrophs maintain cellular energy balance, that is, photostasis to overcome the potential for cellular energy imbalance in their low temperature environments. Photopsychrophiles are photosynthetic organisms that are obligately adapted to low temperature (0⁰- 15 °C) but usually die at higher temperatures (≥20 °C). In contrast, photopsychrotolerant species can usually tolerate and survive a broad range of temperatures (5⁰- 40 °C). First, we summarize the basic concepts of excess excitation energy, energy balance, photoprotection and photostasis and their importance to survival in polar habitats. Second, we compare the photoprotective mechanisms that underlie photostasis and survival in aquatic cyanobacteria and green algae as well as terrestrial Antarctic and Arctic plants. We show that polar photopsychrophilic and photopsychrotolerant organisms attain energy balance at low temperature either through a regulated reduction in the efficiency of light absorption or through enhanced capacity to consume photosynthetic electrons by the induction of O₂ as an alternative electron acceptor. Finally, we compare the published genomes of three photopsychrophilic and one photopsychrotolerant alga with five mesophilic green algae including the model green alga, Chlamydomonas reinhardtii. We relate our genomic analyses to photoprotective mechanisms that contribute to the potential attainment of photostasis. Finally, we discuss how the observed genomic redundancy in photopsychrophilic genomes may confer energy balance, photoprotection and resilience to their harsh polar environment. Primary production in aquatic, Antarctic and Arctic environments is dependent on diverse algal and cyanobacterial communities. Although mosses and lichens dominate the Antarctic terrestrial landscape, only two extant angiosperms exist in the Antarctic. The identification of a single 'molecular key' to unravel adaptation of photopsychrophily and photopsychrotolerance remains elusive. Since these photoautotrophs represent excellent biomarkers to assess the impact of global warming on polar ecosystems, increased study of these polar photoautotrophs remains essential.

Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) reveals multiple metabolism alterations in microalgae induced by cadmium and mercury

Toxic metals such as cadmium (Cd) and mercury (Hg) represent a threat to photosynthetic organisms of polluted aquatic ecosystems, and knowledge about mechanisms of toxicity is essential for appropriate assessment of environmental risks. We used Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) to characterise major changes of biomolecules caused by Cd and Hg in the model green microalga Chlamydomonas reinhardtii. μSR-FTIR showed several metabolic alterations in different biochemical groups such as carbohydrates, proteins, and lipids in a time-dose dependent manner, with the strongest changes occurring at concentrations above 10 μM Cd and 15 μM Hg after short-term (24 h) treatments. This occurred in a context where metals triggered intracellular oxidative stress and chloroplast damage, along with autophagy induction by overexpressing AUTOPHAGY-RELATED PROTEIN 8 (ATG8). Thin layer chromatography analysis confirmed that toxic metals promoted remarkable changes in lipid profile, with higher degree of esterified fatty acid unsaturation as detected by gas chromatography coupled with mass spectrometry. Under Cd stress, there was specifically higher unsaturation of free fatty acids, while Hg led to stronger unsaturation in monogalactosyldiacylglycerol. μSR-FTIR spectroscopy proved as a valuable tool to identify biochemical alterations in microalgae, information that could be exploited to optimise approaches for metal decontamination.

Quantitative proteomic comparison of salt stress in Chlamydomonas reinhardtii and the snow alga Chlamydomonas nivalis reveals mechanisms for salt-triggered fatty acid accumulation via reallocation of carbon resources

BACKGROUND

Chlamydomonas reinhardtii is a model green alga strain for molecular studies; its fully sequenced genome has enabled omic-based analyses that have been applied to better understand its metabolic responses to stress. Here, we characterised physiological and proteomic changes between a low-starch C. reinhardtii strain and the snow alga Chlamydomonas nivalis, to reveal insights into their contrasting responses to salinity stress.

RESULTS

Each strain was grown in conditions tailored to their growth requirements to encourage maximal fatty acid (as a proxy measure of lipid) production, with internal controls to allow comparison points. In 0.2 M NaCl, C. nivalis accumulates carbohydrates up to 10.4% DCW at 80 h, and fatty acids up to 52.0% dry cell weight (DCW) over 12 days, however, C. reinhardtii does not show fatty acid accumulation over time, and shows limited carbohydrate accumulation up to 5.5% DCW. Analysis of the C. nivalis fatty acid profiles showed that salt stress improved the biofuel qualities over time. Photosynthesis and respiration rates are reduced in C. reinhardtii relative to C. nivalis in response to 0.2 M NaCl. De novo sequencing and homology matching was used in conjunction with iTRAQ-based quantitative analysis to identify and relatively quantify proteomic alterations in cells exposed to salt stress. There were abundance differences in proteins associated with stress, photosynthesis, carbohydrate and lipid metabolism proteins. In terms of lipid synthesis, salt stress induced an increase in dihydrolipoyl dehydrogenase in C. nivalis (1.1-fold change), whilst levels in C. reinhardtii remained unaffected; this enzyme is involved in acetyl CoA production and has been linked to TAG accumulation in microalgae. In salt-stressed C. nivalis there were decreases in the abundance of UDP-sulfoquinovose (- 1.77-fold change), which is involved in sulfoquinovosyl diacylglycerol metabolism, and in citrate synthase (- 2.7-fold change), also involved in the TCA cycle. Decreases in these enzymes have been shown to lead to increased TAG production as fatty acid biosynthesis is favoured. Data are available via ProteomeXchange with identifier PXD018148.

CONCLUSIONS

These differences in protein abundance have given greater understanding of the mechanism by which salt stress promotes fatty acid accumulation in the un-sequenced microalga C. nivalis as it switches to a non-growth state, whereas C. reinhardtii does not have this response.

Increasing DNA content for cost-effective oil production in Parachlorella kessleri

The aim of this work was to study salt stress effects on DNA content and oil production processes integrating harvesting, lipid accumulation and oil extraction. Salt-induced enlargement of Parachlorella kessleri cells, with increasing content of DNA and neutral lipid were found. The 34.77% neutral lipid content and biomass concentration of 0.83 g L^-1 were obtained after 7 days of salt treatment, compared with that of 13.57% and 0.89 g L^-1 cultivated under normal condition. Sedimentation efficiency increased markedly from 15% to 90% due to the cell enlargement. Disruption fraction and the recovery rate of total lipids of wet cells under salt stress were significantly higher than that of normal conditions (100% and 82.4% for salt stress vs.76.8% and 51.1% for normal conditions). This work demonstrated that salt-induced increase in cell size and DNA content was an effective strategy for the enhancement of oil production, microalgae harvesting and oil extraction.

Variation of fatty acid desaturation in response to different nitrate levels in Auxenochlorella pyrenoidosa

Microalgae are promising feedstocks for biodiesel, where the high proportion of monounsaturated fatty acid such as oleic acid (C18:1) is preferred. To regulate fatty acid desaturation in microalgae, the relationship among nitrate concentration, fatty acid composition and the expression levels of desaturase genes was explored. Dynamic variations of fatty acid profiles suggested nitrate could induce desaturation of C18 fatty acids. The content of C18:1 in Auxenochlorella pyrenoidosa was 30.88% at 0 g l^-1 nitrate concentration compared with 0.48% at 1.5 g l^-1. The expressions of relative delta-9, 12 and 15 fatty acid desaturase genes (Δ9, Δ12 and Δ15FADs) were further investigated. The 330% upregulated expression of Δ9FAD in logarithmic phase at 0 g l^-1 resulted in C18:1 accumulation. Moreover, nitrate replenishment caused a sharp reduction of C18:1 from 34.79% to 0.22% and downregulation of Δ9FAD expression to 1% of the nitrate absence level, indicating the pivotal role of Δ9FAD in C18:1 accumulation. Finally, overexpression of Δ9FAD in Escherichia coli and Saccharomyces cerevisiae resulted in an increase of C18:1, confirming its ability of desaturating C18:0. The results could provide a new approach and scientific guidance for the improvement of biodiesel quality and industrialization of high-valued chemicals by means of metabolic engineering.

The Antarctic sea ice alga Chlamydomonas sp. ICE-L provides insights into adaptive patterns of chloroplast evolution

BACKGROUND

The ice alga Chlamydomonas sp. ICE-L is the main contributor to primary productivity in Antarctic sea ice ecosystems and is well adapted to the extremely harsh environment. However, the adaptive mechanism of Chlamydomonas sp. ICE-L to sea-ice environment remains unclear. To study the adaptive strategies in Chlamydomonas sp. ICE-L, we investigated the molecular evolution of chloroplast photosynthetic genes that are essential for the accumulation of carbohydrate and energy living in Antarctic sea ice.

RESULTS

The 60 chloroplast protein-coding genes of Chlamydomonas sp. ICE-L were obtained, and the branch-site test detected significant signatures of positive selection on atpB, psaB, and rbcL genes in Chlamydomonas sp. ICE-L associated with the photosynthetic machinery. These positively selected genes were further identified as being under convergent evolution between Chlamydomonas sp. ICE-L and the halotolerant alga Dunaliella salina.

CONCLUSIONS

Our study provides evidence that the phototrophic component of Chlamydomonas sp. ICE-L exhibits adaptive evolution under extreme environment. The positive Darwinian selection operates on the chloroplast protein-coding genes of Antarctic ice algae adapted to extreme environment following functional-specific and lineages-specific patterns. In addition, three positively selected genes with convergent substitutions in Chlamydomonas sp. ICE-L were identified, and the adaptive modifications in these genes were in functionally important regions of the proteins. Our study provides a foundation for future experiments on the biochemical and physiological impacts of photosynthetic genes in green algae.

The first (6-4) photolyase with DNA damage repair activity from the Antarctic microalga Chlamydomonas sp. ICE-L

The psychrophilic microalga, Chlamydomonas sp. ICE-L, isolated from floating ice in the Antarctic, one of the most highly UV exposed ecosystems on Earth, displays an efficient DNA photorepair capacity. Here, the first known (6-4) photolyase gene (6-4CiPhr) from C. sp. ICE-L was identified. The 6-4CiPhr encoded 559-amino acid polypeptide with a pI of 8.86, and had a predicted Mw of 64.2 kDa. Real-time PCR was carried out to investigate the response of 6-4CiPhr to UVB exposure. The transcription of 6-4CiPhr was up-regulated continuously within 6 h, achieving a maximum of 62.7-fold at 6 h. Expressing 6-4CiPhr in a photolyase-deficient Escherichia coli strain improved survival rate of the strain. In vitro activity assays of purified protein demonstrated that 6-4CiPhr was a photolyase with 6-4PP repair activity. These findings improve understanding of photoreactivation mechanisms of (6-4) photolyase.

Production of lutein, and polyunsaturated fatty acids by the acidophilic eukaryotic microalga Coccomyxa onubensis under abiotic stress by salt or ultraviolet light

In this study, the effect of abiotic stress on the acidophilic eukaryotic microalga, Coccomyxa onubensis, was analyzed for the production of lutein and PUFAs (polyunsaturated fatty acids). It grows autotrophically at a pH of 2.5. It showed a growth rate of 0.30 d^-1, and produced approximately 122.50 mg·L^-1·d^-1 biomass, containing lipids (300.39 mg g^-1dw), lutein (5.30 mg g^-1dw), and β-carotene (1.20 mg g^-1dw). The fatty acid methyl ester (FAME) fraction was 89.70 mg g^-1dw with abundant palmitic acid (28.70%) and linoleic acid (37.80%). The addition of 100 mM NaCl improved the growth rate (0.54 d^-1), biomass productivity (243.75 mg·L^-1·d^-1), and lipids accumulation (416.16 mg g^-1dw). The microalga showed a lutein content of 6.70 mg g^-1dw and FAME fraction of 118.90 mg g^-1dw; 68% of the FAMEs were PUFAs. However, when 200-500 mM salt was added, its growth was inhibited but there was a significant induction of lutein (up to 7.80 mg g^-1dw). Under continuous illumination with PAR (photosynthetically active radiations) +UVA (ultraviolet A, 8.7 W m^-2), C. onubensis showed a growth rate of 0.40 d^-1, and produced 226.3 mg·L^-1·d^-1 biomass, containing lipids, (487.26 mg g^-1dw), lutein (7.07 mg g^-1dw), and FAMEs (232.9 mg g^-1dw); 48.4% of the FAME were PUFAs. The illumination with PAR + UVB (ultraviolet B, 0.16 W m^-2) was toxic for cells. These results indicate that C. onubensis biomass is suitable as a supplement for functional foods and/or source of high added value products.

Effect of salinity stress on growth, lipid productivity, fatty acid composition, and biodiesel properties in Acutodesmus obliquus and Chlorella vulgaris

Two microalgae strains including Chlorella vulgaris and Acutodesmus obliquus were grown on BG11 medium with salinity stress ranging from 0.06 to 0.4 M NaCl. Highest lipid content in C. vulgaris and A. obliquus was 49 and 43% in BG11 amended with 0.4 M NaCl. The microalgal strains C. vulgaris and A. obliquus grow better at 0.06 M NaCl concentration than control condition. At 0.06 M NaCl, improved dry biomass content in C. vulgaris and A. obliquus was 0.92 and 0.68 gL^-1, respectively. Stress biomarkers like reactive oxygen species, antioxidant enzyme catalase, and ascorbate peroxidase were also lowest at 0.06 M NaCl concentration revealing that both the microalgal strains are well acclimatized at 0.06 M NaCl concentration. The fatty acid composition of the investigated microalgal strains was also improved by increased NaCl concentration. At 0.4 M NaCl, palmitic acid (37%), oleic acid (15.5%), and linoleic acid (20%) were the dominant fatty acids in C. vulgaris while palmitic acid (54%) and stearic acid (26.6%) were major fatty acids found in A. obliquus. Fatty acid profiling of C. vulgaris and A. obliquus significantly varied with salinity concentration. Therefore, the study showed that salt stress is an effective stress that could increase not only the lipid content but also improved the fatty acid composition which could make C. vulgaris and A. obliquus potential strains for biodiesel production.

Genome-wide identification of membrane-bound fatty acid desaturase genes in Gossypium hirsutum and their expressions during abiotic stress

Membrane-bound fatty acid desaturases (FADs) are of great importance and play multiple roles in plant growth and development. In the present study, 39 full-length FAD genes, based on database searches, were identified in tetraploid upland cotton (Gossypium hirsutum L.) and were phylogenetically clustered into four subfamilies. Genomic localization revealed that 34 genes were mapped on 22 chromosomes, and five genes were positioned on the scaffold sequences. The FAD genes of G. hirsutum in the same subfamily had similar gene structures. The structures of paralogous genes were considerably conserved in exons number and introns length. It was suggested that the FAD gene families in G. hirsutum might be duplicated mainly by segmental duplication. Moreover, the FAD genes were differentially expressed in different G. hirsutum tissues in response to different levels of salt and cold stresses, as determined by qRT-PCR analysis. The identification and functional analysis of FAD genes in G. hirsutum may provide more candidate genes for genetic modification.

Effects of different photoperiod and trophic conditions on biomass, protein and lipid production by the marine alga Nannochloropsis gaditana at optimal concentration of desalination concentrate

This study investigated the cultivation of the marine alga Nannochloropsis gaditana in a medium based on desalination concentrate (DC) with an optimal concentration of 75% DC, under three trophic conditions and four photoperiod schedules. N. gaditana produced a peak biomass concentration (1.25gL^-1) under mixotrophic culture condition and a photoperiod of 16L:08D. N. gaditana cells compensate to different light-dark regimes producing different amounts of protein (17.9-44.8%). The intracellular lipid content in N. gaditana cells increased both under autotrophic conditions with a 16L:08D cycle (16.7%), and under mixotrophic conditions with a 08L:16D cycle (15.7%). In heterotrophic culture, N. gaditana cells were rich in polyunsaturated fatty acids (46.0%). This study demonstrates an alternative approach to enhancing intracellular lipid content of the marine alga N. gaditana by modifying the photoperiod, trophic conditions and stress-salinity-conductivity with the use of a DC-based medium.

The Search for a Lipid Trigger: The Effect of Salt Stress on the Lipid Profile of the Model Microalgal Species Chlamydomonas reinhardtii for Biofuels Production

BACKGROUND

Algal cells produce neutral lipid when stressed and this can be used to generate biodiesel.

OBJECTIVE

Salt stressed cells of the model microalgal species Chlamydomonas reinhardtii were tested for their suitability to produce lipid for biodiesel.

METHODS

The starchless mutant of C. reinhardtii (CC-4325) was subjected to salt stress (0.1, 0.2 and 0.3 M NaCl) and transesterification and GC analysis were used to determine fatty acid methyl ester (FAME) content and profile.

RESULTS

Fatty acid profile was found to vary under salt stress conditions, with a clear distinction between 0.1 M NaCl, which the algae could tolerate, and the higher levels of NaCl (0.2 and 0.3 M), which caused cell death. Lipid content was increased under salt conditions, either through long-term exposure to 0.1 M NaCl, or short-term exposure to 0.2 and 0.3 M NaCl. Palmitic acid (C16:0) and linolenic acid (C18:3n3) were found to increase significantly at the higher salinities.

CONCLUSION

Salt increase can act as a lipid trigger for C. reinhardtii.

Transcriptome differences between fiber-type and seed-type Cannabis sativa variety exposed to salinity

The industrial hemp varieties 'Yunma 5' and 'Bamahuoma,' which demonstrate growth vigor and environmental adaptability, have been primarily cultivated in Yunnan and Guangxi, China, respectively, for fiber and seeds. The results of physiological measurements showed the phenotypic differences between the two varieties in response to salt stress. RNA-Seq analysis was first performed on leaves of both varieties sampled at four time intervals (0, 2, 4, 6 days) after treatment with salt (500 mM NaCl) We identified 220 co-up-regulated differentially expressed genes (DEGs) in the two varieties, while 26 up-regulated DEGs and 24 down-regulated DEGs were identified exclusively in the single varieties after 2 days of salt stress. Among the 220 DEGs, we identified 22 transcription factors, including key transcription factors involved in salt stress, such as MYB, NAC, GATA, and HSF. We applied gene expression profile analysis and found that 'Yunma 5' and 'Bamahuoma' have variety-specific pathways for resisting salt stress. The DEGs of 'Yunma 5' were enriched in spliceosome and amino acid metabolism genes, while the DEGs of 'Bamahuoma' were enriched in fatty acid metabolism, amino acid metabolism, and endoplasmic reticulum protein processing pathway. Although there were common DEGs, such as genes encoding cysteine protease and alpha/beta-hydrolase superfamily, the two varieties' responses to salt stress impacted different metabolic pathways. The DEGs that were co-expressed in both varieties under stress may provide useful insights into the tolerance of cultivated hemp and other bast fiber crops to saline soil conditions. These transcriptomes also represent reference sequences for industrial hemp.

Acclimation of Antarctic Chlamydomonas to the sea-ice environment: a transcriptomic analysis

The Antarctic green alga Chlamydomonas sp. ICE-L was isolated from sea ice. As a psychrophilic microalga, it can tolerate the environmental stress in the sea-ice brine, such as freezing temperature and high salinity. We performed a transcriptome analysis to identify freezing stress responding genes and explore the extreme environmental acclimation-related strategies. Here, we show that many genes in ICE-L transcriptome that encoding PUFA synthesis enzymes, molecular chaperon proteins, and cell membrane transport proteins have high similarity to the gens from Antarctic bacteria. These ICE-L genes are supposed to be acquired through horizontal gene transfer from its symbiotic microbes in the sea-ice brine. The presence of these genes in both sea-ice microalgae and bacteria indicated the biological processes they involved in are possibly contributing to ICE-L success in sea ice. In addition, the biological pathways were compared between ICE-L and its closely related sister species, Chlamydomonas reinhardtii and Volvox carteri. In ICE-L transcripome, many sequences homologous to the plant or bacteria proteins in the post-transcriptional, post-translational modification, and signal-transduction KEGG pathways, are absent in the nonpsychrophilic green algae. These complex structural components might imply enhanced stress adaptation capacity. At last, differential gene expression analysis at the transcriptome level of ICE-L indicated that genes that associated with post-translational modification, lipid metabolism, and nitrogen metabolism are responding to the freezing treatment. In conclusion, the transcriptome of Chlamydomonas sp. ICE-L is very useful for exploring the mutualistic interaction between microalgae and bacteria in sea ice; and discovering the specific genes and metabolism pathways responding to the freezing acclimation in psychrophilic microalgae.

Biomass, lipid productivities and fatty acids composition of marine Nannochloropsis gaditana cultured in desalination concentrate

In this study the feasibility of growing marine Nannochloropsis gaditana in desalination concentrate (DC) was explored and the influence of the DC concentration on the biomass growth, lipid productivities and fatty acids composition was assessed. The reuse of the medium with the optimum DC concentration in successive algal cultivation cycles and the additional of a carbon source to the optimized medium were also evaluated. On varying the DC concentration, the maximum biomass concentration (0.96gL(-1)) and lipid content (12.6%) were obtained for N. gaditana in the medium with the optimum DC concentration (75%). Over the course of the reuse of the optimum DC medium, three cultivation cycles were performed, observing that the biomass productivity is directly correlated to lipid productivity. Palmitic acid was the major fatty acid found in N. gaditana cells. The saturated fatty acids content of the algae enhanced significantly on increasing the DC concentration.

Cyclobutane pyrimidine dimers photolyase from extremophilic microalga: remarkable UVB resistance and efficient DNA damage repair

Bacteria living in the Antarctic region have developed several adaptive features for growth and survival under extreme conditions. Chlamydomonas sp. ICE-Lis well adapted to high levels of solar UV radiation. A putative photolyase was identified in the Chlamydomonas sp. ICE-L transcriptome. The complete cDNA sequence was obtained by RACE-PCR. This PHR encoding includes a polypeptide of 579 amino acids with clear photolyase signatures belonging to class II CPD-photolyases, sharing a high degree of homology with Chlamydomonas reinhardtii (68%). Real-time PCR was performed to investigate the potential DNA damage and responses following UVB exposure. CPD photolyase mRNA expression level increased over 50-fold in response to UVB radiation for 6h. Using photolyase complementation assay, we demonstrated that DNA photolyase increased photo-repair more than 116-fold in Escherichia coli strain SY2 under 100μw/cm(2) UVB radiation. To determine whether photolyase is active in vitro, CPD photolyase was over-expressed. It was shown that pyrimidine dimers were split by the action of PHR2. This study reports the unique structure and high activity of the enzyme. These findings are relevant for further understanding of molecular mechanisms of photo-reactivation, and will accelerate the utilization of photolyase in the medical field.

Microalgal lipids biochemistry and biotechnological perspectives

In the last few years, there has been an intense interest in using microalgal lipids in food, chemical and pharmaceutical industries and cosmetology, while a noteworthy research has been performed focusing on all aspects of microalgal lipid production. This includes basic research on the pathways of solar energy conversion and on lipid biosynthesis and catabolism, and applied research dealing with the various biological and technical bottlenecks of the lipid production process. In here, we review the current knowledge in microalgal lipids with respect to their metabolism and various biotechnological applications, and we discuss potential future perspectives. The committing step in fatty acid biosynthesis is the carboxylation of acetyl-CoA to form malonyl-CoA that is then introduced in the fatty acid synthesis cycle leading to the formation of palmitic and stearic acids. Oleic acid may also be synthesized after stearic acid desaturation while further conversions of the fatty acids (i.e. desaturations, elongations) occur after their esterification with structural lipids of both plastids and the endoplasmic reticulum. The aliphatic chains are also used as building blocks for structuring storage acylglycerols via the Kennedy pathway. Current research, aiming to enhance lipogenesis in the microalgal cell, is focusing on over-expressing key-enzymes involved in the earlier steps of the pathway of fatty acid synthesis. A complementary plan would be the repression of lipid catabolism by down-regulating acylglycerol hydrolysis and/or β-oxidation. The tendency of oleaginous microalgae to synthesize, apart from lipids, significant amounts of other energy-rich compounds such as sugars, in processes competitive to lipogenesis, deserves attention since the lipid yield may be considerably increased by blocking competitive metabolic pathways. The majority of microalgal production occurs in outdoor cultivation and for this reason biotechnological applications face some difficulties. Therefore, algal production systems need to be improved and harvesting systems need to be more effective in order for their industrial applications to become more competitive and economically viable. Besides, a reduction of the production cost of microalgal lipids can be achieved by combining lipid production with other commercial applications. The combined production of bioactive products and lipids, when possible, can support the commercial viability of both processes. Hydrophobic compounds can be extracted simultaneously with lipids and then purified, while hydrophilic compounds such as proteins and sugars may be extracted from the defatted biomass. The microalgae also have applications in environmental biotechnology since they can be used for bioremediation of wastewater and to monitor environmental toxicants. Algal biomass produced during wastewater treatment may be further valorized in the biofuel manufacture. It is anticipated that the high microalgal lipid potential will force research towards finding effective ways to manipulate biochemical pathways involved in lipid biosynthesis and towards cost effective algal cultivation and harvesting systems, as well.

Biodiesel quality and biochemical changes of microalgae Chlorella pyrenoidosa and Scenedesmus obliquus in response to nitrate levels

Biodiesel quality associated with biochemical components of Chlorella pyrenoidosa and Scenedesmus obliquus under different nitrate levels were investigated. The highest lipid contents of 54.5% for C. pyrenoidosa and 47.7% for S. obliquus were obtained in nitrate absence. Carbohydrate peaked at 0.3gL(-1) with values of 40.7% for C. pyrenoidosa and 42.5% for S. obliquus. Protein content seemed species dependent, which decreased substantially to 11.2% in C. pyrenoidosa and 8.8% in S. obliquus under nitrate absence in present research. Better biodiesel quality (e.g. cetane number >58, iodine value <69) could be obtained from C. pyrenoidosa in nitrate absence and S. obliquus in 0.3gL(-1), where the highest saturated fatty acids (39.5 for C. pyrenoidosa, 31.2 for S. obliquus) and the lowest unsaturated fatty acids (60.5 for C. pyrenoidosa, 68.8 for S. obliquus) were obtained. These results suggest that microalgae grown in the presence of nitrogen may limit biodiesel quality.

Polar Microalgae: New Approaches towards Understanding Adaptations to an Extreme and Changing Environment

Polar Regions are unique and highly prolific ecosystems characterized by extreme environmental gradients. Photosynthetic autotrophs, the base of the food web, have had to adapt physiological mechanisms to maintain growth, reproduction and metabolic activity despite environmental conditions that would shut-down cellular processes in most organisms. High latitudes are characterized by temperatures below the freezing point, complete darkness in winter and continuous light and high UV in the summer. Additionally, sea-ice, an ecological niche exploited by microbes during the long winter seasons when the ocean and land freezes over, is characterized by large salinity fluctuations, limited gas exchange, and highly oxic conditions. The last decade has been an exciting period of insights into the molecular mechanisms behind adaptation of microalgae to the cryosphere facilitated by the advancement of new scientific tools, particularly "omics" techniques. We review recent insights derived from genomics, transcriptomics, and proteomics studies. Genes, proteins and pathways identified from these highly adaptable polar microbes have far-reaching biotechnological applications. Furthermore, they may provide insights into life outside this planet, as well as glimpses into the past. High latitude regions also have disproportionately large inputs into global biogeochemical cycles and are the region most sensitive to climate change.