Impacts of microplastic and seawater acidification on unicellular red algae: Growth response, photosynthesis, antioxidant enzymes, and extracellular polymer substances.

Microplastics (MPs) pollution and seawater acidification have increasingly become huge threats to the ocean ecosystem. Their impacts on microalgae are of great importance, since microalgae are the main primary producers and play a critical role in marine ecosystems. However, the impact of microplastics and acidification on unicellular red algae, which have a unique phycobiliprotein antenna system, remains unclear. Therefore, the impacts of polystyrene-MPs alone and the combined effects of MPs and seawater acidification on the typical unicellular marine red algae Porphyridium purpureum were investigated in the current study. The result showed that, under normal seawater condition, microalgae densities were increased by 17.75-41.67 % compared to the control when microalgae were exposed to small-sized MPs (0.1 µm) at concentrations of 5-100 mg L-1. In addition, the photosystem II and antioxidant enzyme system were not subjected to negative effects. The large-sized MPs (1 µm) boosted microalgae growth at a low concentration of MPs (5 mg L-1). However, it was observed that microalgae growth was significantly inhibited when MPs concentration increased up to 50 and 100 mg L-1, accompanied by the remarkably reduced Fv/Fm value and the elevated levels of SOD, CAT enzymes, phycoerythrin (PE), and extracellular polysaccharide (EPS). Compared to the normal seawater condition, microalgae densities were enhanced by 52.11-332.56 % under seawater acidification, depending on MPs sizes and concentrations, due to the formed CO2-enrichment condition and appropriate pH range. PE content in microalgal cells was significantly enhanced, but SOD and CAT activities as well as EPS content markedly decreased under acidification conditions. Overall, the impacts of seawater acidification were more pronounced than MPs impacts on microalgae growth and physiological responses. These findings will contribute to a substantial understanding of the effects of MPs on marine unicellular red microalgae, especially in future seawater acidification scenarios.

Maximizing Polysaccharides and Phycoerythrin in Porphyridium purpureum via the Addition of Exogenous Compounds: A Response-Surface-Methodology Approach.

Phycoerythrin and polysaccharides have significant commercial value in medicine, cosmetics, and food industries due to their excellent bioactive functions. To maximize the production of biomass, phycoerythrin, and polysaccharides in Porphyridium purpureum, culture media were supplemented with calcium gluconate (CG), magnesium gluconate (MG) and polypeptides (BT), and their optimal amounts were determined using the response surface methodology (RSM) based on three single-factor experiments. The optimal concentrations of CG, MG, and BT were determined to be 4, 12, and 2 g L-1, respectively. The RSM-based models indicated that biomass and phycoerythrin production were significantly affected only by MG and BT, respectively. However, polysaccharide production was significantly affected by the interactions between CG and BT and those between MG and BT, with no significant effect from BT alone. Using the optimized culture conditions, the maximum biomass (5.97 g L-1), phycoerythrin (102.95 mg L-1), and polysaccharide (1.42 g L-1) concentrations met and even surpassed the model-predicted maximums. After optimization, biomass, phycoerythrin, and polysaccharides concentrations increased by 132.3%, 27.97%, and 136.67%, respectively, compared to the control. Overall, this study establishes a strong foundation for the highly efficient production of phycoerythrin and polysaccharides using P. purpureum.

Enhanced microalgal biomass and lipid production with simultaneous effective removal of Cd using algae-bacteria-activated carbon consortium added with organic carbon source.

Recently, using microalgae to remediate heavy metal polluted water has been attained a huge attention. However, heavy metals are generally toxic to microalgae and consequently decrease biomass accumulation. To address this issue, the feasibility of adding exogenous glucose, employing algae-bacteria system and algae-bacteria-activated carbon consortium to enhance microalgae growth were evaluated. The result showed that Cd2+ removal efficiency was negatively correlated with microalgal specific growth rate. The exogenous glucose alleviated the heavy metal toxicity to algal cells and thus increased the microalgae growth rate. Among the different treatments, the algae-bacteria-activated carbon combination had the highest biomass concentration (1.15 g L-1) and lipid yield (334.97 mg L-1), which were respectively 3.03 times of biomass (0.38 g L-1) and 4.92 times of lipid yield (68.08 mg L-1) in the single microalgae treatment system. Additionally, this algae-bacteria-activated carbon consortium remained a high Cd2+ removal efficiency (91.61%). In all, the present study developed an approach that had a great potential in simultaneous heavy metal wastewater treatment and microalgal lipid production.

Paracoccus marinaquae sp. nov., isolated from coastal water of the Yellow Sea.

A Gram-stain-negative, non-motile and coccoid bacterial strain, designated XHP0099T, was isolated from the coastal water of the Yellow Sea, China. Growth occurred at 20-37 â„ƒ (optimum, 28 â„ƒ), pH 5.0-9.0 (optimum, pH 7.0-8.0), and with 0-7.0% NaCl (optimum, 2.0-3.0%). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain XHP0099T was related to members of the genus Paracoccus and shared the highest sequence similarity with "P. siganidrum" M26 (98.2%), followed by P. alkanivorans 4-2 T (97.6%) and P. alkenifer DSM 11593 T (97.4%). The average nucleotide identity, amino acid identity, and digital DNA-DNA hybridization values of strain XHP0099T against related members in the genus Paracoccus were below the cut-off points proposed for the delineation of a novel species. The major cellular fatty acids (> 10%) were summed feature 8 (C18:1 ω7c/C18:1 ω6c), and C18:0. The major isoprenoid quinone was Q-10 and the polar lipids contained diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), aminolipid (AL) and unidentified polar lipids (L). The G + C content of the genomic DNA of strain XHP0099T was 66.0%. Genomic analysis suggested that strain XHP0099T harbored gene clusters for formaldehyde and the XoxF-type methanol oxidation and type 1 Calvin cycle, which could confer the methylotrophy pathway. Based on the phenotypic, phylogenetic, biochemical and chemotaxonomic analysis, strain XHP0099T represents a novel species of the genus Paracoccus, for which the name Paracoccus marinaquae sp. nov. is proposed. The type strain is XHP0099T (= JCM 34661 T = GDMCC 1.2414 T = MCCC 1K05846T).

Description of Nocardioides jiangsuensis sp. nov., and Proposal for Reclassification of the Genus Marmoricola as Nocardioides.

A Gram-staining-positive, non-motile, aerobic, spherical actinobacterium, designated WL0053T, was isolated from the coastal sediment of Nantong City, Jiangsu Province, China. The 16S rRNA gene sequence of strain WL0053T exhibited the highest similarities to Nocardioides mesophilus MSL-22T (98.0%), N. massiliensis GD12T (97.8%), Marmoricola bigeumensis MSL-05T (97.6%), and N. jensenii DSM 20641T (97.3%). The polyphasic taxonomic approach was used for the identification of strain WL0053T. This strain formed white, round, and smooth colonies and grew in the presence of 0-18% (w/v) NaCl (optimum, 0-4.0%), at pH 6.0-9.0 (optimum, pH 7.0) and at 20-37 °C (optimum, 28 °C). The main cellular fatty acids comprised of C17:1 ω8c, C18:1 ω9c, and iso-C16:0. The genomic DNA G + C content was 71.9%. The predominant quinone was MK-8(H4), and the major polar lipid consisted of phosphatidylcholine, glycolipid, phosphatidylethanolamine, and two unidentified phospholipids. Phylogenetic trees of 16S rRNA gene and bac120 gene set indicted that strain WL0053T was closely related to the species N. iriomotensis and N. mesophilus, while these two species clustered in a separate clade together with M. caldifontis YIM 730233T in the bac120 tree. Combined with the analysis of average nucleotide identity (ANI), average amino acid identity (AAI), and digital DNA-DNA hybridization (dDDH), it can be considered that the strain WL0053T is a new member of the genus Nocardioides and is proposed to be named as Nocardioides jiangsuensis sp. nov.. The type strain is WL0053T (=MCCC 1K05897T=JCM 34671T=GDMCC 4.192T). Furthermore, based on the fact that the genera Nocardioides and Marmoricola both appeared polyphyletic with no significant difference on phenotypic and chemotaxonomic traits, we proposed to reclassify the genus Marmoricola as Nocardioides.

Aestuariicella albida sp. nov., isolated from surface water of the Yellow Sea, and proposal of the genus Aestuariicella as a member of the family Cellvibrionaceae.

A Gram-stain-negative, non-motile and aerobic bacterium, designated HHU G3-2T, was isolated from surface water of the Yellow Sea, PR China. Strain HHU G3-2T was positive for oxidase activity and negative for catalase. Optimal growth occurred at 28 °C (range, 20-37 °C), pH 7.0 (range, pH 6.0-9.0) and in the presence of 2-5 % (w/v) NaCl (range, 1-7%). Phylogenetic analysis based on 16S rRNA gene sequences and 120 ubiquitous single-copy protein-coding genes indicated that strain HHU G3-2T formed a distinct phylogenetic lineage with Aestuariicella hydrocarbonica JCM 30134T, sharing a 16S rRNA gene sequence similarity of 98.05%. Average nucleotide identity and digital DNA-DNA hybridization values between strain HHU G3-2T and A. hydrocarbonica JCM 30134T were 75.74 and 17.80%, respectively, which were below the threshold values of 95-96 and 70 %, respectively. The DNA G+C content of the genomic DNA was 51.17 mol%. The major fatty acids (>10 %) were C17 : 1 ω8c (19.8 %), summed feature 3 (C16 : 1 ω7c/C16 : 1 ω6c; 15.9 %), summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c; 13.8 %) and C17 : 0 (10.3 %). The predominant isoprenoid quinone was ubiquinone-8. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. Based on the polyphasic taxonomic data, strain HHU G3-2T represents a novel species of the genus Aestuariicella, for which the name Aestuariicella albida sp. nov. is proposed. The type strain is HHU G3-2T (=MCCC 1K04224T=JCM 34652T=GDMCC 1.2418T=CGMCC 1.17397T). In addition, we proposed the genus Aestuariicella as a member of the family Cellvibrionaceae.

Hyphomonas sediminis sp. nov., isolated from marine sediment.

A Gram-staining-negative, aerobic and pear-shaped bacterial strain, designated WL0036T, was isolated from coastal sediment sample collected in Nantong city, Jiangsu province of China (120° 51' 13″ E, 32° 6' 26″ N) in October 2020. Strain WL0036T was found to grow at 20-37 °C (optimum, 28 °C) with 0-9.0% NaCl (optimum, 2.5-4.0%) and displayed alkaliphilic growth with the pH range of pH 6.0-10.0 (optimum, pH 7.0-8.0). The polar lipids profile of strain WL0036T included phosphatidylcholine, phosphatidylethanolamine, glycolipid and an unidentified lipid. The major isoprenoid quinone was determined to be Q-11 and the major fatty acids were C16:0, 11-methyl-C18:1ω7c, and summed features 8 (C18:1ω6c and/or C18:1ω7c). The G + C content of genomic DNA was 61.8%. Phylogenetic trees constructed based on 16S rRNA gene sequence and bac120 gene set (a collection of 120 single-copy protein sequences prevalent in bacteria) indicted that strain WL0036T clustered with strains Hyphomonas neptunium ATCC 15444T and H. polymorpha PS728T. The average nucleotide identities between strain WL0036T and strains H. neptunium ATCC 15444T and H. polymorpha PS728T were 80.7% and 81.2%, respectively. Strain WL0036T showed 22.8% and 23.2% of digital DNA-DNA hybridization identities with H. neptunium ATCC 15444T and H. polymorpha PS728T, respectively. As inferred from the phenotypic and genotypic characteristics and the phylogenetic trees, strain WL0036T ought to be recognized as a novel species in genus Hyphomonas, for which the name Hyphomonas sediminis sp. nov. is proposed. The type strain is WL0036T (= MCCC 1K05843T = JCM 34658T = GDMCC 1.2413T).

Sphingopyxis jiangsuensis sp. nov. Isolated From the Surface Water of the Yellow Sea.

A novel bacterium, designated strain XHP0097T, was isolated from the surface water of the Yellow Sea, China. The cells were Gram-stain-negative, aerobic, rod-shaped, yellow-colored, and non-motile on 2216E agar. Optimal growth of strain XHP0097T occurs at 28 °C and pH 7.0 with the presence of NaCl concentration 2% (w/v). According to the analysis of comparative 16S rRNA gene sequence, strain XHP0097T showed the highest 16S rRNA gene sequence similarity with Sphingopyxis panaciterrulae KCTC 22112T (98.2%). Phylogenetic analysis based on 16S rRNA gene sequences as well as on 120 ubiquitous single-copy protein-coding genes supported that strain XHP0097T formed a distinct phyletic lineage as a new species within the genus Sphingopyxis. Strain XHP0097T showed an average nucleotide identity value and a digital DNA-DNA hybridization (dDDH) of 79.1-81.7% and 21.9-24.4% to the members of the genus Sphingopyxis, respectively. According to genome sequence, the DNA G + C content of XHP0097T was 64.8%. The major fatty acids (>10%) were C16:0 (17.5%), summed feature 3 (C16:1ω7c and/or C16:1ω6c) (15.1%), and summed feature 8 (C18:1ω7c and/or C18:1ω6c) (19.2%). The major polar lipids of strain XHP0097T were phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), and sphingoglycolipid (SGL). Q-10 was the predominant respiratory quinone. Characteristics of physiological and biochemical, phylogenetic, and chemotaxonomic analysis demonstrated the isolate XHP0097T represents a novel species of the genus Sphingopyxis, for which the name Sphingopyxis jiangsuensis sp. nov. is proposed. The type strain is XHP0097T (=MCCC 1K05845T = GDMCC 1.2415T = JCM 34678T).

Heterotrophic and mixotrophic cultivation of microalgae to simultaneously achieve furfural wastewater treatment and lipid production.

Furfural wastewater (FWW) treatment is important in modern chemical production. However, traditional wastewater treatment methods are inappropriate for the treatment of FWW. In this work, Chlorella pyrenoidosa was employed to study the growth and pollutants removal with both heterotrophic and mixotrophic cultures. The results show that the biomass and removal efficiency for COD and TN were the highest under 10-fold dilution. However, TP removal were inconsistent when the algae were cultivated in both mixotrophic and heterotrophic modes. Compared to high nitrogen (0.75 g/L NaNO3), the algal cells grew faster when adding 0.25 g/L NaNO3 to the FWW, whether in mixotrophic or heterotrophic conditions. The total lipid content in heterotrophic conditions was 18.53%, which was higher than the values in mixotrophy when the concentration of NaNO3 was 0.75 g/L. Different carbon assimilation mechanisms of the algal cells result in a discrepancy in cell growth and pollutant removal, under different culture modes.

The optimization of centrifugal pump driving horizontal tubular photobioreactor for enhancing astaxanthin production using heterotrophic Haematococcus pluvialis.

Haematococcus pluvialis is the prime source of natural astaxanthin for commercial exploitation. The large-scale cultivation of H. pluvialis is one of the key technologies for the development of natural astaxanthin industry. So far, horizontal tubular photobioreactor (HTPBR) circulated by a centrifugal pump has been the main PBR for the large-scale cultivation of H. pluvialis. Shear stress is a negative factor in microalgal cultivation at different scales, particularly for large-scale cultivation. To reduce the adverse impact of shear stress, the tolerance of H. pluvialis to the shear stress during the induction stage was first investigated in this study. H. pluvialis aplanospore was not sensitive to stresses between 19.18 and 27.32 Pa, but was resulted in about 30% cell death under shear stress between 27.32 and 63.84 Pa. Accordingly, two centrifugal pumps with different impellers was selected in 400 L HTPBRs to study the outdoor photoinduction for astaxanthin accumulation. The highest astaxanthin productivity and astaxanthin concentration were obtained in HTPBRs using a centrifugal pump equipped with three unshrouded backward-bladed impellers. The HTPBR was then successfully scaled up to 800 L with a similar performance, showing good scalability.

Actirhodobacter atriluteus gen. nov., sp. nov., isolated from the surface water of the Yellow Sea.

A Gram-stain-negative, aerobic, orange-pigmented bacterial strain, designated HHU K3-1 T, was isolated from the surface water of the Yellow Sea. The strain was observed to grow on 2216E agar medium, and growth occurred at pH 6.0-8.0 (optimum 7.0), 28-37 °C (optimum 28 °C), and in the presence of 0.5-5% (w/v) NaCl (optimum 1-3%). The major fatty acids (> 10%) were summed feature 3 (C16:1ω6c/C16:1ω7c), C17:1ω6c and summed feature 8 (C18:1ω6c/C18:1ω7c). Strain HHU K3-1 T was found to contain ubiquinone-10 as the predominant quinone and the major polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and sphingoglycolipid (SGL). The 16S rRNA gene sequence analysis indicated that strain HHU K3-1 T shared highest similarities with Pelagerythrobacter marensis KCTC 22370 T (97.7%) and Qipengyuania oceanensis MCCC 1A09965T (96.9%). However, a phylogenetic tree based on 288 orthologous clusters (OCs) indicated that HHU K3-1 T was close related to Parapontixanthobacter aurantiacus MCCC 1A09962T. The pairwise AAI and evolutionary distance between HHU K3-1 T and Parapontixanthobacter aurantiacus MCCC 1A09962T are 67.1% and 0.43, respectively, which meet the recently proposed standard to differentiate genera in the family Erythrobacteraceae. On the basis of the result obtained by the polyphasic taxonomic study, strain HHU K3-1 T can be considered to represent a novel genus in the family Erythrobacteraceae, for which the name Actirhodobacter atriluteus gen. nov., sp. nov. is proposed. The type strain is HHU K3-1 T (= MCCC 1K04225T = KCTC 72834 T = CGMCC 1.17395 T).

Modeling and improving arrayed microalgal biofilm attached culture system.

A microalgal biofilm-attached-system is an alternative cultivation method, that offers potential advantages of improved biomass productivity, efficient harvesting, and water saving. These biofilm systems have been widely tested and utilized for microalgal biomass production and wastewater treatment. This research a microalgal growth model for the biofilm attached culture system has been developed and experimentally validated, both, in single and arrayed biofilm systems. It has been shown that the model has the capability to accurately describe microalgae growth. Moreover, via the model simulation, it was observed that system structural parameters, light dilution rate, and light intensity significantly affected the culture performance. The limitations, and improvement aspects of the model, are also discussed in this study. To our knowledge, this is the first time that a mathematical model for an arrayed-biofilm-attached-system has been developed and validated. This model will certainly be helpful in the design, improvement, optimization, and evaluation of the biofilm-attached-systems.

Description of Salinimonas profundi sp. nov., a deep-sea bacterium harboring a transposon Tn6333.

A Gram-staining-negative bacterium, strain HHU 13199T, was isolated from a marine sediment sample collected from South China Sea (119°19.896'E, 19°41.569'N) at a depth of 2918 m. The 16S rRNA gene sequence analysis indicated that strain HHU 13199T represents a member of the genus Salinimonas with the highest sequence similarity (99.8%) to the type strain S. iocasae KX18D6T. However, the average nucleotide identity values and digital DNA-DNA hybridization between strain HHU 13199T and closely related members of the genus Salinimonas were all below the cut-off level (95-96 % and 70%, respectively) for species delineation. This strain grew with sea salt of 0.5-18% (w/v) (optimum, 2-5%), but no growth observed when using NaCl instead. The major fatty acids are C16:0, summed feature 3 (C16:1ω7c and/or C16:1ω6c), and summed feature 8 (C18:1ω7c and/or C18:1ω6c). The predominant isoprenoid quinone is ubiquinone-8. The polar lipids mainly consist of phosphatidylethanolamine, and phosphatidylglycerol. Genomic characterization revealed that strain HHU 13199T harbors a distinct type I-F CRISPR-Cas system and plenty of genes associated with heavy metal resistance, including a transposon (Tn6333) conferring mercury resistance. In addition, a phylogenetic tree based on the bac120 core genes suggested that the genus Salinimonas should be a subclade within Alteromonas. On the basis of the phenotypic, phylogenetic and chemotaxonomic characterizations, strain HHU 13199T represents a novel species of the genus Salinimonas, for which the name Salinimonas profundi sp. nov. is proposed. The type strain is HHU 13199T (= KCTC 72837T = MCCC 1K04127T).

Sphingomonas hominis sp. nov., isolated from hair of a 21-year-old girl.

A Gram-stain-negative, aerobic, motile strain, HHU CXWT, was isolated from hair of a healthy 21-year-old female student of Hohai University, Nanjing, China. The 16S rRNA gene sequence analysis indicated that HHU CXWT represents a member of the genus Sphingomonas with the highest sequence similarity (97.6%) to the type strain S. aquatilis JSS7T. HHU CXWT grew at 4-35 °C and pH 6-8, with optimum growth at 28 °C and pH 7. Tolerance to NaCl was up to 2% (w/v) with optimum growth in 0.5-1.0% NaCl. The major fatty acids were C16:0, C17:1ω6c, C18:1ω7c11-methyl, summed feature 3 (C16:1ω7c and/or C16:1ω6c), and summed feature 8 (C18:1ω7c and/or C18:1ω6c). The predominant isoprenoid quinone was ubiquinone-10. The polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), sphingoglycolipid (SGL), phosphatidylinositol mannosides (PIM), and an unidentified glycolipid (GL). The DNA G + C content was 67.1%. The average nucleotide identity (ANI) values and digital DNA-DNA hybridization (dDDH) between HHU CXWT and closely related members of the genus Sphingomonas were all below the cut-off level (95-96% and 70%, respectively) for species delineation. On the basis of the phenotypic, phylogenetic and chemotaxonomic characterizations, HHU CXWT represents a novel species of the genus Sphingomonas, for which the name Sphingomonas hominis sp. nov. is proposed. The type strain is HHU CXWT (= KCTC 72946T = CGMCC 1.17504T = MCCC 1K04223T).

Development of a novel multi-column airlift photobioreactor with easy scalability by means of computational fluid dynamics simulations and experiments.

Aiming to culture algae with high efficiency, a novel vertical multi-column airlift photobioreactor (VMAPBR) has been developed. It was constructed with a series of vertically arranged parallel columns with easy scalability. The hydrodynamic, irradiation and shear stress characteristics of the photobioreactor were studied by computational fluid dynamics (CFD). Accordingly, the optimal aeration manner and aeration rate were determined. When the novel airlift PBR was alternately aerated with aeration rate of 0.2vvm, the biomass concentration of Chlorella pyrenoidosa under outdoor condition reached 1.30gL-1 within the prototype PBR and was further increased to 1.56gL-1 within the optimized PBR. The result of cultivation experiment had good agreement with that of CFD prediction.

A new technology of CO2 supplementary for microalgae cultivation on large scale - A spraying absorption tower coupled with an outdoor open runway pond.

An effective CO2 supply system of a spraying absorption tower combined with an outdoor ORWP (open raceway pond) for microalgae photoautotrophic cultivation is developed in this paper. The microalgae yield, productivity and CO2 fixation efficiency were investigated, and compared with those of bubbling method. The maximum yield and productivity of biomass were achieved 0.927gL(-1) and 0.114gL(-1)day(-1), respectively. The fixation efficiency of CO2 by microalgae with the spraying tower reached 50%, whereas only 11.17% for bubbling method. Pure CO2 can be used in the spraying absorption tower, and the flow rate was only about one third of the bubbling cultivation. It shows that this new method of quantifiable control CO2 supply can meet the requirements of the growth of microalgae cultivation on large-scale.

Investigation on novel raceway pond with inclined paddle wheels through simulation and microalgae culture experiments.

The open raceway ponds are nowadays the most used large-scale reactors for microalgae culture. To avoid the stacking of microalgae, the paddle wheels are the most widely used to circulate and mix the culture medium. In this paper, a numerical simulation using computational fluid dynamics (CFD) was used to investigate the hydrodynamic characteristics of open raceway ponds with different types of paddle wheels (the traditional paddle wheels and the novel paddle wheels with specially inclined angle of the blades). The particle image velocimetry (PIV) was used to validate the reliability of the CFD model. The CFD simulation results showed that the novel raceway pond with 15° inclined angle of the blades had the best mixing efficiency under the same power consumption. Lastly, the results of microalgae culture experiments showed that the growth rates of Chlorella pyrenoidosa in the novel raceway pond with 15° inclined angle of the blades were higher than those in the traditional reactor. The results of the culture experiments and CFD simulations were identical with each other. Therefore, a novel paddle wheel with 15° inclined angle of the blades was obtained for better microalgae cultivation.

Genomic Foundation of Starch-to-Lipid Switch in Oleaginous Chlorella spp.

The ability to rapidly switch the intracellular energy storage form from starch to lipids is an advantageous trait for microalgae feedstock. To probe this mechanism, we sequenced the 56.8-Mbp genome of Chlorella pyrenoidosa FACHB-9, an industrial production strain for protein, starch, and lipids. The genome exhibits positive selection and gene family expansion in lipid and carbohydrate metabolism and genes related to cell cycle and stress response. Moreover, 10 lipid metabolism genes might be originated from bacteria via horizontal gene transfer. Transcriptomic dynamics tracked via messenger RNA sequencing over six time points during metabolic switch from starch-rich heterotrophy to lipid-rich photoautotrophy revealed that under heterotrophy, genes most strongly expressed were from the tricarboxylic acid cycle, respiratory chain, oxidative phosphorylation, gluconeogenesis, glyoxylate cycle, and amino acid metabolisms, whereas those most down-regulated were from fatty acid and oxidative pentose phosphate metabolism. The shift from heterotrophy into photoautotrophy highlights up-regulation of genes from carbon fixation, photosynthesis, fatty acid biosynthesis, the oxidative pentose phosphate pathway, and starch catabolism, which resulted in a marked redirection of metabolism, where the primary carbon source of glycine is no longer supplied to cell building blocks by the tricarboxylic acid cycle and gluconeogenesis, whereas carbon skeletons from photosynthesis and starch degradation may be directly channeled into fatty acid and protein biosynthesis. By establishing the first genetic transformation in industrial oleaginous C. pyrenoidosa, we further showed that overexpression of an NAD(H) kinase from Arabidopsis (Arabidopsis thaliana) increased cellular lipid content by 110.4%, yet without reducing growth rate. These findings provide a foundation for exploiting the metabolic switch in microalgae for improved photosynthetic production of food and fuels.

Sequential Heterotrophy-Dilution-Photoinduction Cultivation of Haematococcus pluvialis for efficient production of astaxanthin.

A novel cultivation strategy called "Sequential Heterotrophy-Dilution-Photoinduction" was successfully applied in the cultivation of Haematococcus pluvialis to produce astaxanthin effectively. Cells were first cultivated heterotrophically to achieve a high cell density, then were diluted to a suitable concentration and switched to a favorable environment for cells acclimation. Finally, the culture was transferred to high light environment for astaxanthin accumulation. By this strategy, the dry cell weight of 26 g/L and biomass productivity of 64.1mg/L/h were obtained in heterotrophy stage which surpassed ever before reported in literatures. Meanwhile, the cells could accumulate considerable astaxanthin up to 4.6% of dry cell weight after 10 days of photoinduction. Furthermore, the application prospects of the strategy were confirmed further by outdoor experiments. Therefore, this novel strategy provided a promising approach for high-efficient production of natural astaxanthin from H. pluvialis to meet the huge demand of this high value product.

Improving performance of flat-plate photobioreactors by installation of novel internal mixers optimized with computational fluid dynamics.

A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The effects of mixer were theoretically evaluated using computational fluid dynamics (CFD) according to radial velocity of fluid and light/dark cycles within reactors. The structure parameters, including the riser width, top clearance, clearance between the baffles and walls, and number of the chambers were further optimized. The microalgae culture test aiming at validating the simulated results was conducted indoor. The results showed the maximum biomass concentrations in the optimized and archetype reactors were 32.8% (0.89 g L(-1)) and 19.4% (0.80 g L(-1)) higher than that in the control reactor (0.67 g L(-1)). Therefore, the novel mixer can significantly increase the fluid velocity along the light attenuation and light/dark cycles, thus further increased the maximum biomass concentration. The PBRs with novel mixers are greatly applicable for high-efficiency cultivation of microalgae.