Design, construction and application of algae-bacteria synergistic system for treating wastewater.

The wastewater treatment technology of algae-bacteria synergistic system (ABSS) is a promising technology which has the advantages of low energy consumption, good treatment effect and recyclable high-value products. In this treatment technology, the construction of an ABSS is a very important factor. At the same time, the emergence of some new technologies (such as microbial fuel cells and bio-carriers, etc.) has further enriched constructing the novel ABSS, which could improve the efficiency of wastewater treatment and the biomass harvesting rate. Thus, this review focuses on the construction of a novel ABSS in wastewater treatment in order to provide useful suggestions for the technology of wastewater treatment.

Overexpression of MPV17/PMP22-like protein 2 gene decreases production of radical oxygen species in Pyropia yezoensis (Bangiales, Rhodophyta).

The northward shift of Pyropia yezoensis aquaculture required the breeding of germplasms with tolerance to the oxidative stress due to the high light conditions of the North Yellow Sea area. The MPV17/PMP22 family proteins were identified as a molecule related to reactive oxygen species (ROS) metabolism. Here, one of the MPV17 homolog genes designated as PyM-LP2 was selected for functional identification by introducing the encoding sequence region/reverse complementary fragment into the Py. yezoensis genome. Although the photosynthetic activity, the respiratory rate, and the ROS level in wild type (WT) and different gene-transformed algal strains showed similar levels under normal conditions, the overexpression (OE) strain exhibited higher values of photosynthesis, respiration, and reducing equivalents pool size but lower intracellular ROS production under stress conditions compared with the WT. Conversely, all the above parameters showed opposite variation trends in RNAi strain as those in the OE strain. This implied that the PyM-LP2 protein was involved in the mitigation of the oxidative stress. Sequence analysis revealed that this PyM-LP2 protein was assorted to peroxisomes and might serve as a poring channel for transferring malate (Mal) to peroxisomes. By overexpressing PyM-LP2, the transfer of Mal from chloroplasts to peroxisomes was enhanced under stress conditions, which promoted photorespiration and ultimately alleviated excessive reduction of the photosynthetic electron chain. This research lays the groundwork for the breeding of algae with enhanced resistance to oxidative stresses.

HSP70A promotes the photosynthetic activity of marine diatom Phaeodactylum tricornutum under high temperature.

With global climate change, the high-temperature environment has severely impacted the community structure and phenotype of marine diatoms. Phaeodactylum tricornutum, a model species of marine diatom, is sensitive to high temperature, which grow slowly under high temperature. However, the regulatory mechanism of P. tricornutum in response to high-temperature is still unclear. In this study, we found that the expression level of the HSP70A in the wild type (WT) increased 28 times when exposed to high temperature (26°C) for 1 h, indicating that HSP70A plays a role in high temperature in P. tricornutum. Furthermore, overexpression and interference of HSP70A have great impact on the exponential growth phase of P. tricornutum under 26°C. Moreover, the results of Co-immunoprecipitation (Co-IP) suggested that HSP70A potentially involved in the correct folding of the photosynthetic system-related proteins (D1/D2), preventing aggregation. The photosynthetic activity results demonstrated that overexpression of HSP70A improves non-photochemical quenching (NPQ) activity under high-temperature stress. These results reveal that HSP70A regulates the photosynthetic activity of P. tricornutum under high temperatures. This study not only helps us to understand the photosynthetic activity of marine diatoms to high temperature but also provides a molecular mechanism for HSP70A in P. tricornutum under high-temperature stress.

SLC24A-mediated calcium exchange as an indispensable component of the diatom cell density-driven signaling pathway.

Diatom bloom is characterized by a rapid increase of population density. Perception of population density and physiological responses can significantly influence their survival strategies, subsequently impacting bloom fate. The population density itself can serve as a signal, which is perceived through chemical signals or chlorophyll fluorescence signals triggered by high cell density, and their intracellular signaling mechanisms remain to be elucidated. In this study, we focused on the model diatom, Phaeodactylum tricornutum, and designed an orthogonal experiment involving varying cell densities and light conditions, to stimulate the release of chemical signals and light-induced chlorophyll fluorescence signals. Utilizing RNA-Seq and Weighted Gene Co-expression Network Analysis, we identified four gene clusters displaying density-dependent expression patterns. Within these, a potential hub gene, PtSLC24A, encoding a Na+/Ca2+ exchanger, was identified. Based on molecular genetics, cellular physiology, computational structural biology, and in situ oceanic data, we propose a potential intracellular signaling mechanism related to cell density in marine diatoms using Ca2+: upon sensing population density signals mediated by chemical cues, the membrane-bound PtSLC24A facilitates the efflux of Ca2+ to maintain specific intracellular calcium levels, allowing the transduction of intracellular density signals, subsequently regulating physiological responses, including cell apoptosis, ultimately affecting algal blooms fate. These findings shed light on the calcium-mediated intracellular signaling mechanism of marine diatoms to changing population densities, and enhances our understanding of diatom bloom dynamics and their ecological implications.

Cryptochrome PtCPF1 regulates high temperature acclimation of marine diatoms through coordination of iron and phosphorus uptake.

Increasing ocean temperatures threaten the productivity and species composition of marine diatoms. High temperature response and regulation are important for the acclimation of marine diatoms to such environments. However, the molecular mechanisms behind their acclimation to high temperature are still largely unknown. In this study, the abundance of PtCPF1 homologs (a member of the cryptochrome-photolyase family in the model diatom Phaeodactylum tricornutum) transcripts in marine phytoplankton is shown to increase with rising temperature based on Tara Oceans datasets. Moreover, the expression of PtCPF1 in P. tricornutum at high temperature (26 °C) was much higher than that at optimum temperature (20 °C). Deletion of PtCPF1 in P. tricornutum disrupted the expression of genes encoding two phytotransferrins (ISIP2A and ISIP1) and two Na+/P co-transporters (PHATRDRAFT_47667 and PHATRDRAFT_40433) at 26 °C. This further impacted the uptake of Fe and P, and eventually caused the arrest of cell division. Gene expression, Fe and P uptake, and cell division were restored by rescue with the native PtCPF1 gene. Furthermore, PtCPF1 interacts with two putative transcription factors (BolA and TF IIA) that potentially regulate the expression of genes encoding phytotransferrins and Na+/P co-transporters. To the best of our knowledge, this is the first study to reveal PtCPF1 as an essential regulator in the acclimation of marine diatoms to high temperature through the coordination of Fe and P uptake. Therefore, these findings help elucidate how marine diatoms acclimate to high temperature.

Morphological characteristics and genetic diversity of floating and attached Ulva prolifera--A case study in the Yellow Sea, China.

Green tides in the Yellow Sea have occurred periodically since 2007, impacting the ecological environment and green algal communities along the coasts of Jiangsu and Shandong provinces in China. To investigate the morphological characteristics and genetic diversity of Ulva prolifera, we conducted surveys and comparative analyses of both its floating and attached forms along the coastal areas of Jiangsu and Shandong. The results revealed that the external morphology of the floating U. prolifera was multibranched. The attached U. prolifera displayed significant morphological variation among individuals. Based on the analysis of the amplified characteristic bands of the chloroplast gene, it was shown that both floating and attached U. prolifera could hybridize with Ulva linza. The genetic diversity of U. prolifera was studied using mitochondrial and chloroplast genome fragments. All floating U. prolifera and three strains of attached U. prolifera belonged to the same haplotype. The genetic diversity of floating U. prolifera was low, and there were some genetic differences with attached U. prolifera. The attached U. prolifera displayed a higher level of genetic diversity with abundant sites of variation and haplotypes.

Algal-bacterial consortium promotes carbon sink formation in saline environment.

INTRODUCTION: The level of atmospheric CO2 has continuously been increasing and the resulting greenhouse effects are receiving attention globally. Carbon removal from the atmosphere occurs naturally in various ecosystems. Among them, saline environments contribute significantly to the global carbon cycle. Carbonate deposits in the sediments of salt lakes are omnipresent, and the biological effects, especially driven by halophilic microalgae and bacteria, on carbonate formation remain to be elucidated. OBJECTIVES: The present study aims to characterize the carbonates formed in saline environments and demonstrate the mechanisms underlying biological-driven CO2 removal via microalgal-bacterial consortium. METHODS: The carbonates naturally formed in saline environments were collected and analyzed. Two saline representative organisms, the photosynthetic microalga Dunaliella salina and its mutualistic halophilic bacteria Nesterenkonia sp. were isolated from the inhabiting saline environment and co-cultivated to study their biological effects on carbonates precipitation and isotopic composition. During this process, electrochemical parameters and Ca2+ flux, and expression of genes related to CaCO3 formation were analyzed. Genome sequencing and metagenomic analysis were conducted to provide molecular evidence. RESULTS: The results showed that natural saline sediments are enriched with CaCO3 and enrichment of genes related to photosynthesis and ureolysis. The co-cultivation stimulated 54.54% increase in CaCO3 precipitation and significantly promoted the absorption of external CO2 by 49.63%. A pH gradient was formed between the bacteria and algae culture, creating 150.22 mV of electronic potential, which might promote Ca2+ movement toward D. salina cells. Based on the results of lab-scale induction and 13C analysis, a theoretical calculation indicates a non-negligible amount of 0.16 and 2.3 Tg C/year carbon sequestration in China and global saline lakes, respectively. CONCLUSION: The combined effects of these two typical representative species have contributed to the carbon sequestration in saline environments, by promoting Ca2+ influx and increase of pH via microalgal and bacterial metabolic processes.

Innovative Eco-Friendly Microwave-Assisted Rapid Biosynthesis of Ag/AgCl-NPs Coated with Algae Bloom Extract as Multi-Functional Biomaterials with Non-Toxic Effects on Normal Human Cells.

Harmful algal blooms impact human welfare and are a global concern. Sargassum spp., a type of algae or seaweed that can potentially bloom in certain regions of the sea around Thailand, exhibits a noteworthy electron capacity as the sole reducing and stabilizing agent, which suggests its potential for mediating nanoparticle composites. This study proposes an eco-friendly microwave-assisted biosynthesis (MAS) method to fabricate silver nanoparticles coated with Sargassum aqueous extract (Ag/AgCl-NPs-ME). Ag/AgCl-NPs-ME were successfully synthesized in 1 min using a 20 mM AgNO3 solution without additional hazardous chemicals. UV-visible spectroscopy confirmed their formation through a surface plasmon resonance band at 400-500 nm. XRD and FTIR analyses verified their crystalline nature and involvement of organic molecules. TEM and SEM characterization showed well-dispersed Ag/AgCl-NPs-ME with an average size of 36.43 nm. The EDS results confirmed the presence of metallic Ag+ and Cl- ions. Ag/AgCl-NPs-ME exhibited significant antioxidant activity against free radicals (DPPH, ABTS, and FRAP), suggesting their effectiveness. They also inhibited enzymes (tyrosinase and ACE) linked to diseases, indicating therapeutic potential. Importantly, the Ag/AgCl-NPs-ME displayed remarkable cytotoxicity against cancer cells (A375, A549, and Caco-2) while remaining non-toxic to normal cells. DNA ladder and TUNEL assays confirmed the activation of apoptosis mechanisms in cancer cells after a 48 h treatment. These findings highlight the versatile applications of Ag/AgCl-NPs-ME in food, cosmetics, pharmaceuticals, and nutraceuticals.

Naturally Occurring Functional Ingredient from Filamentous Thermophilic Cyanobacterium Leptolyngbya sp. KC45: Phytochemical Characterizations and Their Multiple Bioactivities.

Cyanobacteria are rich in phytochemicals, which have beneficial impacts on the prevention of many diseases. This study aimed to comprehensively characterize phytochemicals and evaluate multifunctional bioactivities in the ethanolic extract of the cyanobacterium Leptolyngbya sp. KC45. Results found that the extract mainly contained chlorophylls, carotenoids, phenolics, and flavonoids. Through LC-ESI-QTOF-MS/MS analysis, 38 phenolic compounds with promising bioactivities were discovered, and a higher diversity of flavonoids was found among the phenolic compounds identified. The extract effectively absorbed the harmful UV rays and showed high antioxidant activity on DPPH, ABTS, and PFRAP. The extract yielded high-efficiency inhibitory effects on enzymes (tyrosinase, collagenase, ACE, and α-glucosidase) related to diseases. Interestingly, the extract showed a strong cytotoxic effect on cancer cells (skin A375, lung A549, and colon Caco-2), but had a much smaller effect on normal cells, indicating a satisfactory level of safety for the extract. More importantly, the combination of the DNA ladder assay and the TUNEL assay proved the appearance of DNA fragmentation in cancer cells after a 48 h treatment with the extract, confirming the apoptosis mechanisms. Our findings suggest that cyanobacterium extract could be potentially used as a functional ingredient for various industrial applications in foods, cosmetics, pharmaceuticals, and nutraceuticals.

Overexpression of a novel gene (Pt2015) endows the commercial diatom Phaeodactylum tricornutum high lipid content and grazing resistance.

BACKGROUND: The marine diatom Phaeodactylum tricornutum is a commercially viable species due to its bioactive substances and lipid productivity. Increasing attention has been paid to the isolation or genetic modification of species or strains with a rapid growth rate and large quantities of lipids. Furthermore, contamination of microzooplankton has been one of the major constraints in P. tricornutum large-scale cultivation, which adversely affects growth and greatly impedes the course of biomass production industrialization. RESULTS: Here, based on our previous transcriptomics of P. tricornutum, we found a novel gene (ID: 7202015, hereafter called Pt2015) which affects morphotype of P. tricornutum. Pt2015 protein is located in the plastid, which is highly homologous to part of the sequences of exosome component. The morphotype of the Pt2015 knockout strain (termed 2015KO) using CRISPR/Cas9 method is fusiform, but the Pt2015 overexpression strain (termed oeT) demonstrates a majority triradiate morphotype (approximately 95%) which is stable and has been cultured for more than 200 generations. In addition, the oeT strain demonstrated a similar growth rate to the WT and simultaneously accumulated larger lipids droplets that increased by approximately 30% compared to that of the WT. More importantly, the grazing rate of the amoebae cultured in the oeT strain significantly decreased in comparison with that cultured in WT, suggesting that the oeT can effectively avoid being eaten by microzooplankton. CONCLUSIONS: Therefore, the oeT strain not only improves our understanding of morphotype conversion in diatoms but also demonstrates potential applications for large-scale cultivation of P. tricornutum.

The Complex of Phycobiliproteins, Fucoxanthin, and Krill Oil Ameliorates Obesity through Modulation of Lipid Metabolism and Antioxidants in Obese Rats.

Phycobiliproteins, fucoxanthin, and krill oil are natural marine products with excellent activities. In the study, we prepared the complex of phycobiliproteins, fucoxanthin, and krill oil (PFK) and assessed the anti-obesity, lipid-lowering, and antioxidant activities in high-fat diet rats. The results showed that the rats significantly and safely reduced body weight gain and regulated serum biochemical parameters at 50 mg/kg phycobiliproteins, 10 mg/kg fucoxanthin, and 100 mg/kg krill oil. Furthermore, the molecular mechanism study suggested that the complex of PFK confined the enzyme activities of lipid synthesis and enhanced antioxidant activity to improve obesity indirectly. The conclusions demonstrated that the complex of PFK has potent anti-obesity and hypolipidemic effects which have potential use as a natural and healthy food and medicine for anti-obesity and lowering blood lipids in the future.

Transcriptomic and metabolic signatures of diatom plasticity to light fluctuations.

Unlike in terrestrial and freshwater ecosystems, light fields in oceans fluctuate due to both horizontal current and vertical mixing. Diatoms thrive and dominate the phytoplankton community in these fluctuating light fields. However, the molecular mechanisms that regulate diatom acclimation and adaptation to light fluctuations are poorly understood. Here, we performed transcriptome sequencing, metabolome profiling, and 13C-tracer labeling on the model diatom Phaeodactylum tricornutum. The diatom acclimated to constant light conditions was transferred to six different light conditions, including constant light (CL5d), short-term (1 h) high light (sHL1h), and short-term (1 h) and long-term (5 days) mild or severe light fluctuation conditions (mFL1h, sFL1h, mFL5d, and sFL5d) that mimicked land and ocean light levels. We identified 2,673 transcripts (25% of the total expressed genes) expressed differentially under different fluctuating light regimes. We also identified 497 transcription factors, 228 not reported previously, which exhibited higher expression under light fluctuations, including 7 with a light-sensitive PAS domain (Per-period circadian protein, Arnt-aryl hydrocarbon receptor nuclear translocator protein, Sim-single-minded protein) and 10 predicted to regulate genes related to light-harvesting complex proteins. Our data showed that prolonged preconditioning in severe light fluctuation enhanced photosynthesis in P. tricornutum under this condition, as evidenced by increased oxygen evolution accompanied by the upregulation of Rubisco and light-harvesting proteins. Furthermore, severe light fluctuation diverted the metabolic flux of assimilated carbon preferentially toward fatty acid storage over sugar and protein. Our results suggest that P. tricornutum use a series of complex and different responsive schemes in photosynthesis and carbon metabolism to optimize their growth under mild and severe light fluctuations. These insights underscore the importance of using more intense conditions when investigating the resilience of phytoplankton to light fluctuations.

Structural Characterization of Gracilariopsis lemaneiformis Polysaccharide and Its Property in Delaying Cellular Senescence.

The sulfated polysaccharide was isolated from the purified G. lemaneiformis polysaccharide (PGP), and its property in delaying H2O2-induced 2BS cellular senescence was studied. The results showed that PGP was a linear polysaccharide containing alternating α-(1 → 3)- and ß-(1 → 4)-galactopyranose units. Most of the sulfate groups are at C6 of the -(1 → 4)-α-D-Galp, and a small part of them are at C3 and C6. PGP pretreatment could decrease SA-ß-gal-positive cells and prevent the formation of senescence-associated heterochromatic foci (SAHF) induced by H2O2 in a dose-dependent manner. It is speculated that PGP may delay aging by downregulating the expression of p21 and p53 genes. The finding provides new insights into the beneficial role of G. lemaneiformis polysaccharide (GP) on retarding senescence process.

Carbonic anhydrase isoforms of Neopyropia yezoensis: Intracellular localization and expression profiles in response to inorganic carbon concentration and life stage.

Macroalgae, particularly commercially grown seaweed, substantially contribute to CO2 removal and carbon storage. However, knowledge regarding the CO2 concentrating mechanism (CCM) of macroalgae is limited. Carbonic anhydrase (CA), a key component of the biophysical CCM, plays important roles in many physiological reactions in various organisms. Few characteristics of CA in Neopyropia yezoensis are known, particularly its intracellular location and responses to different concentrations of Ci. We identified, amplified, and characterized 11 putative genes encoding N. yezoensis CA. The predicted corresponding proteins clustered into three subfamilies: α-, ß-, and γ-type. The intracellular localization of seven CA isoforms-one in the chloroplasts, three in the cytoplasm, and three in the mitochondria-was elucidated with fusion proteins. Higher NyCA expression, particularly of certain chloroplastic, cytosolic, and mitochondrial CAs, is observed more often during the foliose stage, thus suggesting that CAs play important roles in development in N. yezoensis.

Metagenomics and network analysis elucidating the coordination between fermentative bacteria and microalgae in a novel bacterial-algal coupling reactor (BACR) for mariculture wastewater treatment.

To achieve the goal of treating mariculture wastewater economically and efficiently, a novel bacterial-algal coupling reactor (BACR) integrating acidogenic fermentation and microalgae cultivation was firstly investigated for mariculture wastewater treatment. Volatile fatty acids (VFAs) generated in the dark chamber migrated into the photo chamber for microalgal utilization, which alleviated the pH drop and feedback inhibition of the acidogenic fermentation. The maximum dry cell weight (DCW) of microalgae was 1.46 g/L, and pollutants such as chemical oxygen demand (COD), ammonium (NH4+-N) and total phosphorus (TP) in the BACR were effectively removed under the mixotrophic culture condition. Furthermore, bacterial community profiles and functional genes in the BACR and single acidogenic fermentation reactor were identified. Compared with the single acidogenic fermentation reactor, most of the fermentative bacteria (e.g., Ruminococcus, Christensenellaceae R-7 group, Exiguobacterium, Pseudomonas and Levilinea) were enriched by the BACR. From the genetic perspective, the abundances of dominant genes (ackA, acs and atoD) associated with acetic, propionic and butyric acid production were greatly enhanced in the BACR. In the fatty acid biosynthesis pathway (ko00061), three kinds of high-abundance acetyl-CoA carboxylase genes and eight kinds of downstream functional genes were up-regulated in the BACR. Finally, based on co-occurrence network analysis, the coordination between fermentative bacteria and microalgae in the BACR was revealed. This study provided a deep insight into the advantage and potential of the BACR in mariculture wastewater treatment.

Improved growth of bait microalgae Isochrysis and aquacultural wastewater treatment with mixotrophic culture.

This research of mixotrophic microalgae Isochrysis 3011 with glycerol was combined with the treatment of aqua-cultural wastewater, different initial concentrations, and optimized light intensities. The algae growth rate, removal efficiencies of total nitrogen (TN) and total phosphorus (TP) were determined. Results showed that the suitable initial concentration was 0.4 g L-1, and the optimum light intensity was 60 µmol m-2 s-1. The growth of the mixotrophic group was better than that of the autotrophic culture. The biomass yield of the mixotrophic group with glycerol was 0.17 g L-1 d-1, and the removal rates of TN and TP were 73.39% and 95.61%, respectively. The content of total lipid and total protein in mixotrophic group were higher than the values of the autotrophic group. This indicates that aquaculture wastewater treatment with mixotrophic bait microalgae can obtain superior micro-algal biomass, which is also a potential technology for wastewater utilization and ecological protection.

Light-harvesting complex stress-related proteins play crucial roles in the acclimation of Physcomitrella patens under fluctuating light conditions.

Photosynthetic organisms have evolved photoprotective mechanisms to acclimate to light intensity fluctuations in their natural growth environments. Photosystem (PS) II subunit S (PsbS) and light-harvesting complex (LHC) stress-related proteins (LhcSR) are essential for triggering photoprotection in vascular plants and green algae, respectively. The activity of both proteins is strongly enhanced in the moss Physcomitrella patens under high-light conditions. However, their role in regulating photosynthesis acclimation in P. patens under fluctuating light (FL) conditions is still unknown. Here, we compare the responses of wild-type (WT) P. patens and mutants lacking PsbS (psbs KO) or LhcSR1 and 2 (lhcsr KO) to FL conditions in which the low-light phases were periodically interrupted with high-light pulses. lhcsr KO mutant showed a strong reduction in growth with respect to WT and psbs KO under FL conditions. The lack of LhcSR not only decreased the level of non-photochemical quenching, resulting in an over-reduced plastoquinone pool, but also significantly increased the PSI acceptor limitation values with respect to WT and psbs KO under FL conditions. Moreover, in lhcsr KO mutant, the abundance of PSI core and PSI-LHCI complex decreased greatly under FL conditions compared with the WT and psbs KO. We proposed that LhcSR in P. patens play a crucial role in moss acclimation to dynamic light changes.

Proteomic and biochemical responses to different concentrations of CO2 suggest the existence of multiple carbon metabolism strategies in Phaeodactylum tricornutum.

BACKGROUND: Diatoms are well known for high photosynthetic efficiency and rapid growth rate, which are not only important oceanic primary producer, but also ideal feedstock for microalgae industrialization. Their high success is mainly due to the rapid response of photosynthesis to inorganic carbon fluctuations. Thus, an in-depth understanding of the photosynthetic carbon fixation mechanism of diatoms will be of great help to microalgae-based applications. This work directed toward the analysis of whether C4 photosynthetic pathway functions in the model marine diatom Phaeodactylum tricornutum, which possesses biophysical CO2-concentrating mechanism (CCM) as well as metabolic enzymes potentially involved in C4 photosynthetic pathway. RESULTS: For P. tricornutum, differential proteome, enzyme activities and transcript abundance of carbon metabolism-related genes especially biophysical and biochemical CCM-related genes in response to different concentrations of CO2 were tracked in this study. The upregulated protein abundance of a carbonic anhydrases and a bicarbonate transporter suggested biophysical CCM activated under low CO2 (LC). The upregulation of a number of key C4-related enzymes in enzymatic activity, transcript and protein abundance under LC indicated the induction of a mitochondria-mediated CCM in P. tricornutum. Moreover, protein abundance of a number of glycolysis, tricarboxylic acid cycle, photorespiration and ornithine-urea cycle related proteins upregulated under LC, while numbers of proteins involved in the Calvin cycle and pentose phosphate pathway were downregulated. Under high CO2 (HC), protein abundance of most central carbon metabolism and photosynthesis-related proteins were upregulated. CONCLUSIONS: The proteomic and biochemical responses to different concentrations of CO2 suggested multiple carbon metabolism strategies exist in P. tricornutum. Namely, LC might induce a mitochondrial-mediated C4-like CCM and the improvement of glycolysis, tricarboxylic acid cycle, photorespiration and ornithine-urea cycle activity contribute to the energy supply and carbon and nitrogen recapture in P. tricornutum to cope with the CO2 limitation, while P. tricornutum responds to the HC environment by improving photosynthesis and central carbon metabolism activity. These findings can not only provide evidences for revealing the global picture of biophysical and biochemical CCM in P. tricornutum, but also provide target genes for further microalgal strain modification to improve carbon fixation and biomass yield in algal-based industry.

Chlorophyll fluorescence as a light signal enhances iron uptake by the marine diatom Phaeodactylum tricornutum under high-cell density conditions.

BACKGROUND: Diatoms usually dominate phytoplankton blooms in open oceans, exhibiting extremely high population densities. Although the iron uptake rate of diatoms largely determines the magnitude and longevity of diatom blooms, the underlying mechanisms regulating iron uptake remain unclear. RESULTS: The transcription of two iron uptake proteins, ISIP2a and ISIP1, in the marine diatom Phaeodactylum tricornutum was enhanced with increasing cell density, whereas the cellular iron content showed the opposite trend. When compared with the wild-type strain, knockdown of ISIP2a resulted in 43% decrease in cellular iron content, implying the involvement of ISIP2a in iron uptake under high-cell density conditions. Incubation of the diatom cells with sonicated cell lysate conditioned by different cell densities did not affect ISIP2a and ISIP1 expression, ruling out regulation via chemical cues. In contrast, ISIP2a and ISIP1 transcription were strongly induced by red light. Besides, chlorophyll fluorescence excited from the blue light was also positively correlated with population density. Subsequently, a "sandwich" illumination incubator was designed to filter out stray light and ensure that the inner layer cells only receive the emitted chlorophyll fluorescence from outer layers, and the results showed that the increase in outer cell density significantly elevated ISIP2a and ISIP1 transcription in inner layer cells. In situ evidence from Tara oceans also showed positively correlated between diatom ISIP transcripts and chlorophyll content. CONCLUSIONS: This study shows that chlorophyll fluorescence derived from neighboring cells is able to upregulate ISIP2a and ISIP1 expression to facilitate iron assimilation under high-cell density. These results provide novel insights into biotic signal sensing in phytoplankton, which can help to elucidate the underlying mechanisms of marine diatom blooms.

Phycobiliprotein as fluorescent probe and photosensitizer: A systematic review.

Phycobiliprotein is a natural product with many biological activities in various seaweeds. Phycobiliproteins have been widely used for anti-oxidation, anti-tumor, anti-inflammatory and immune-enhancing activities as a functional factor. Phycobiliproteins with high purity are considerably more expensive than common. To provide with a systematic, deep and detailed information about those features of phycobiliproteins, we performed a relatively comprehensive analysis on structural composition, the application of phycobiliproteins in the fields of fluorescent probe and photodynamic therapy in this report.