Modulation of starch synthesis in Arabidopsis via phytochrome B-mediated light signal transduction.

Starch is a major storage carbohydrate in plants and is critical in crop yield and quality. Starch synthesis is intricately regulated by internal metabolic processes and external environmental cues; however, the precise molecular mechanisms governing this process remain largely unknown. In this study, we revealed that high red to far-red (high R:FR) light significantly induces the synthesis of leaf starch and the expression of synthesis-related genes, whereas low R:FR light suppress these processes. Arabidopsis phytochrome B (phyB), the primary R and FR photoreceptor, was identified as a critical positive regulator in this process. Downstream of phyB, basic leucine zipper transcription factor ELONGATED HYPOCOTYL5 (HY5) was found to enhance starch synthesis, whereas the basic helix-loop-helix transcription factors PHYTOCHROME INTERACTING FACTORs (PIF3, PIF4, and PIF5) inhibit starch synthesis in Arabidopsis leaves. Notably, HY5 and PIFs directly compete for binding to a shared G-box cis-element in the promoter region of genes encoding starch synthases GBSS, SS3, and SS4, which leads to antagonistic regulation of their expression and, consequently, starch synthesis. Our findings highlight the vital role of phyB in enhancing starch synthesis by stabilizing HY5 and facilitating PIFs degradation under high R:FR light conditions. Conversely, under low R:FR light, PIFs predominantly inhibit starch synthesis. This study provides insight into the physiological and molecular functions of phyB and its downstream transcription factors HY5 and PIFs in starch synthesis regulation, shedding light on the regulatory mechanism by which plants synchronize dynamic light signals with metabolic cues to module starch synthesis.

miR-148a-3p regulates proliferation and apoptosis of idiopathic gingival fibroma by targeting NPTX1.

OBJECTIVE: Idiopathic gingival fibromatosis (IGF) is a rare heterogeneous disease that results in the progressive and diffuse hyperplasia of gingival tissues. MicroRNAs are implicated in the development and progression of various tumors. The present study aimed to explore the potential roles and mechanisms of miR-148a-3p in IGF. METHODS: Gingival fibroblasts (GFs) were transfected with miR-148a-3p mimics, miR-148a-3p inhibitors, or siNPTX1, and then, the proliferation and apoptosis of GFs and the expression of related genes were evaluated using Cell Counting Kit-8 assays, 5-ethynyl-2'-deoxyuridine assays, flow cytometry, reverse transcription-quantitative polymerase chain reaction, and western blot analysis, respectively. RESULTS: miR-148a-3p was highly expressed in GFs of IGF (IGF-GFs) as compared with normal GFs (N-GFs). Overexpression of miR-148a-3p promoted the proliferation and inhibited the apoptosis of N-GFs, whereas downregulation of miR-148a-3p had the opposite effect in IGF-GFs. Knockdown of NPTX1 reversed miR-148a-3p-mediated effects in IGF-GFs. Dual-luciferase reporter assay confirmed that NPTX1 is a direct target of miR-148a-3p. CONCLUSION: These findings identify that miR-148a-3p could regulate cell proliferation and apoptosis by targeting NPTX1, providing new insights for the further study of the molecular mechanism and treatment of IGF.

SbbHLH85, a bHLH member, modulates resilience to salt stress by regulating root hair growth in sorghum.

bHLH family proteins play an important role in plant stress response. However, the molecular mechanism regulating the salt response of bHLH is largely unknown. This study aimed to investigate the function and regulating mechanism of the sweet sorghum SbbHLH85 during salt stress. The results showed that SbbHLH85 was different from its homologs in other species. Also, it was a new atypical bHLH transcription factor and a key gene for root development in sweet sorghum. The overexpression of SbbHLH85 resulted in significantly increased number and length of root hairs via ABA and auxin signaling pathways, increasing the absorption of Na+. Thus, SbbHLH85 plays a negative regulatory role in the salt tolerance of sorghum. We identified a potential interaction partner of SbbHLH85, which was phosphate transporter chaperone PHF1 and modulated the distribution of phosphate, through screening a yeast two-hybrid library. Both yeast two-hybrid and BiFC experiments confirmed the interaction between SbbHLH85 and PHF1. The overexpression of SbbHLH85 led to a decrease in the expression of PHF1 as well as the content of Pi. Based on these results, we suggested that the increase in the Na+ content and the decrease in the Pi content resulted in the salt sensitivity of transgenic sorghum.

WHIRLY1 Regulates HSP21.5A Expression to Promote Thermotolerance in Tomato.

Heat stress poses a major threat to plant productivity and crop yields. The induction of heat shock proteins (HSPs) by heat shock factors is a principal defense response of plants exposed to heat stress. In this study, we identified and analyzed the heat stress-induced Whirly1 (SlWHY1) gene in tomato (Solanum lycopersicum). We generated various SlWHY1-overexpressing (OE) and SlWHY1-RNA interference (RNAi) lines to investigate the role of WHIRLY1 in thermotolerance. Compared with the wild type (WT), the OE lines showed less wilting, as reflected by their increased membrane stability and soluble sugar content and reduced reactive oxygen species (ROS) accumulation under heat stress. By contrast, RNAi lines with inhibited SlWHY1 expression showed the opposite phenotype and corresponding physiological indices under heat stress. The heat-induced gene SlHSP21.5A, encoding an endoplasmic reticulum-localized HSP, was upregulated in the OE lines and downregulated in the RNAi lines compared with the WT. RNAi-mediated inhibition of SlHSP21.5A expression also resulted in reduced membrane stability and soluble sugar content and increased ROS accumulation under heat stress compared with the WT. SlWHY1 binds to the elicitor response element-like element in the promoter of SlHSP21.5A to activate its transcription. These findings suggest that SlWHY1 promotes thermotolerance in tomato by regulating SlHSP21.5A expression.

Molecular mechanisms governing shade responses in maize.

Light is one of the most important environmental factors affecting plant growth and development. Plants use shade avoidance or tolerance strategies to adjust their growth and development thus increase their success in the competition for incoming light. To investigate the mechanism of shade responses in maize (Zea mays), we examined the anatomical and transcriptional dynamics of the early shade response in seedlings of the B73 inbred line. Transcriptome analysis identified 912 differentially expressed genes, including genes involved in light signaling, auxin responses, and cell elongation pathways. Grouping transcription factor family genes and performing enrichment analysis identified multiple types of transcription factors that are differentially regulated by shade and predicted putative core genes responsible for regulating shade avoidance syndrome. For functional analyses, we ectopically over-expressed ZmHB53, a type II HD-ZIP transcription factor gene significantly induced by shade, in Arabidopsis thaliana. Transgenic Arabidopsis plants overexpressing ZmHB53 exhibited narrower leaves, earlier flowering, and enhanced expression of shade-responsive genes, suggesting that ZmHB53 might participates in the regulation of shade responses in maize. This study increases our understanding of the regulatory network of the shade response in maize and provides a useful resource for maize genetics and breeding.

Whirly1 enhances tolerance to chilling stress in tomato via protection of photosystem II and regulation of starch degradation.

In plants, the chilling response involves decreased photosynthetic capacity and increased starch accumulation in chloroplasts. However, the mechanisms that modulate these processes remain unclear. We found that the SlWHY1 gene is significantly induced by chilling stress (4°C) in tomato. Three SlWHY1 overexpression (OE) lines grew better than the wild type (WT) under chilling stress; the OE plants retained intact photosynthetic grana lamellae and showed enhanced hydrolysis of starch. By contrast, RNAi lines that inhibited SlWHY1 were more affected than the corresponding WT cultivar. Their grana lamellae were damaged and starch content increased. The psbA gene encodes the key photosystem II (PSII) protein D1. We show that SlWHY1 binds to the upstream region (A/GTTACCCT/A) of SlpsbA and enhances the de novo synthesis of D1 in chloroplasts. Additionally, SlWHY1 regulates the expression of the starch-degrading enzyme α-amylase (SlAMY3-L) and the starch synthesis-related enzyme isoamylase gene (SlISA2) in the nucleus, thus modulating the starch content in chloroplasts. We demonstrate that SlWHY1 enhances the resistance of tomato to chilling stress by maintaining the function of PSII and degrading starch. Thus, overexpression of WHY1 may be an effective strategy for enhancing resistance to chilling stress of chilling-sensitive crops in agricultural production.

A stress-associated NAC transcription factor (SlNAC35) from tomato plays a positive role in biotic and abiotic stresses.

The NAC transcription factor family participates in responses to various kinds of environmental stimuli in plants. Responses of NAC genes to abiotic stresses have been widely studied, but their functions in response to biotic stress are little reported in plants, especially in crops. In the present study, we examined the functions of a novel tomato (Solanum lycopersicum) NAC protein (SlNAC35) in abiotic and biotic stress resistance by using transgenic tobacco. Expression analysis found that SlNAC35 expression was induced by drought stress, salt stress, bacterial pathogen, and signaling molecules, suggesting its involvement in plant responses to biotic and abiotic stimuli. Moreover, transgenic lines exhibited a greater number of lateral roots and longer root length compared with Vec lines (empty vector lines) after drought and salt treatment. These results indicate that overexpression of SlNAC35 promoted root growth and development under drought and salt stresses. Higher expressions of NtARF1, NtARF2 and NtARF8 were observed under drought and salt stresses in transgenic lines, suggesting that overexpression of SlNAC35 promoted growth and development of roots in transgenic lines possibly by involving auxin signaling and by regulating NtARF expression. In addition, SlNAC35 overexpression improved resistance to bacterial pathogen in transgenic tobacco, and reactive oxygen species may be in the upstream of salicylic acid (SA) signaling in transgenic tobacco during defense response.

A tomato chloroplast-targeted DnaJ protein protects Rubisco activity under heat stress.

Photosynthesis is one of the biological processes most sensitive to heat stress in plants. Carbon assimilation, which depends on ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), is one of the major sites sensitive to heat stress in photosynthesis. In this study, the roles of a tomato (Solanum lycopersicum) chloroplast-targeted DnaJ protein (SlCDJ2) in resisting heat using sense and antisense transgenic tomatoes were examined. SlCDJ2 was found to be uniformly distributed in the thylakoids and stroma of the chloroplasts. Under heat stress, sense plants exhibited higher chlorophyll contents and fresh weights, and lower accumulation of reactive oxygen species (ROS) and membrane damage. Moreover, Rubisco activity, Rubisco large subunit (RbcL) content, and CO2 assimilation capacity were all higher in sense plants and lower in antisense plants compared with wild-type plants. Thus, SlCDJ2 contributes to maintenance of CO2 assimilation capacity mainly by protecting Rubisco activity under heat stress. SlCDJ2 probably achieves this by keeping the levels of proteolytic enzymes low, which prevents accelerated degradation of Rubisco under heat stress. Furthermore, a chloroplast heat-shock protein 70 was identified as a binding partner of SlCDJ2 in yeast two-hybrid assays. Taken together, these findings establish a role for SlCDJ2 in maintaining Rubisco activity in plants under heat stress.

Occupational stress and coping strategies among emergency department nurses of China.

Emergency department(ED) nurses work in a rapidly changing environment with patients that have wide variety of conditions. Occupational stress in emergency department nurses is a common problem. The purpose of this study was to describe the relationship between coping strategies and occupational stress among ED nurses in China. A correlational, cross-sectional design was adopted. Two questionnaires were given to a random sample of 127 ED nurses registered at the Heilongjiang Nurses' Association. Data were collected from the nurses that worked in the ED of five general hospitals in Harbin China. Occupational stress and coping strategies were measured by two questionnaires. A multiple regression model was applied to analyze the relationship between stress and coping strategies. The stressors of ED nurses mainly come from the ED specialty of nursing (2.97±0.55), workload and time distribution (2.97±0.58). The mean score of positive coping strategies was 2.19±0.35, higher than the norm (1.78±0.52). The mean score of negative coping strategies was 1.20±0.61, lower than the norm (1.59±0.66), both had significant statistical difference (P<0.001). Too much documents work, criticism, instrument equipment shortage, night shift, rank of professional were the influence factors about occupational stress to positive coping styles. Too much documents work, and medical insurance for ED nurses were the influential factors on occupational stress to negative coping styles. This study identified several factors associated with occupational stress in ED nurses. These results could be used to guide nurse managers of ED nurses to reduce work stress. The managers could pay more attention to the ED nurse's coping strategies which can further influence their health state and quality of nursing care. Reducing occupational stress and enhancing coping strategies are vital not only for encouraging nurses but also for the future of nursing development.

A chloroplast-targeted DnaJ protein contributes to maintenance of photosystem II under chilling stress.

DnaJ proteins act as essential molecular chaperones in protein homeostasis and protein complex stabilization under stress conditions. The roles of a tomato (Lycopersicon esculentum) chloroplast-targeted DnaJ protein (LeCDJ1), whose expression was upregulated by treatment at 4 and 42 °C, and with high light, NaCl, polyethylene glycol, and H2O2, were investigated here using sense and antisense transgenic tomatoes. The sense plants exhibited not only higher chlorophyll content, fresh weight and net photosynthetic rate, but also lower accumulation of reactive oxygen species and membrane damage under chilling stress. Moreover, the maximal photochemistry efficiency of photosystem II (PSII) (F v/F m) and D1 protein content were higher in the sense plants and lower in the antisense plants, and the photoinhibitory quenching was lower in the sense plants and higher in the antisense plants, suggesting that the inhibition of PSII was less severe in the sense plants and more severe in the antisense plants compared with the wild type. Furthermore, the PSII protein complexes were also more stable in the sense plants. Interestingly, the sense plants treated with streptomycin (SM), an inhibitor of organellar translation, still showed higher F v/F m, D1 protein content and PSII stability than the SM-untreated antisense plants. This finding suggested that the protective effect of LeCDJ1 on PSII was, at least partially, independent of D1 protein synthesis. Furthermore, chloroplast heat-shock protein 70 was identified as the partner of LeCDJ1. These results indicate that LeCDJ1 has essential functions in maintaining PSII under chilling stress.

LeCDJ1, a chloroplast DnaJ protein, facilitates heat tolerance in transgenic tomatoes.

The roles of a tomato (Lycopersicon esculentum) chloroplast-targeted DnaJ protein (LeCDJ1) were investigated using wild-type (WT) and sense transgenic tomatoes. The LeCDJ1 expression was upregulated by 38 °C, 42 °C, 45 °C, NaCl, PEG, methyl viologen (MV) and hydrogen peroxide (H2O2), but not by 30 °C and 35 °C. Meanwhile, LeCDJ1 was involved in the response of plants to abscisic acid (ABA). Under heat stress, the sense plants showed better growth, higher chlorophyll content, lower malondialdehyde (MDA) accumulation and relative electrical conductivity (REC), and also less PSII photoinhibition than WT. Interestingly, the sense plants treated with streptomycin (SM), an inhibitor of organellar translation, still showed higher maximum photochemistry efficiency of PSII (Fv/Fm) and D1 protein levels than the SM-untreated WT, suggesting that the protective effect of LeCDJ1 on PSII was, at least partially, independent of D1 protein synthesis. Furthermore, the relatively lower superoxide radical (O2(•-)) and H2O2 levels in the sense plants were considered to be due to the higher ascorbate peroxidase (APX) and superoxide dismutase (SOD) activity, which seemed unlikely dependent on their transcription level. These results indicated that LeCDJ1 overexpression facilitated heat tolerance in transgenic tomatoes.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives.

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Combined transcriptomic and metabolomic analyses of temperature response of microalgae using waste activated sludge extracts for promising biodiesel production.

Waste activated sludge (WAS) as one of the major pollutants with a significant annual production, has garnered significant attention regarding its treatment and utilization. If improperly discharged, it not only caused environmental pollution but also led to the wastage of valuable resources. In this study, the microalgae growth and lipid accumulation using waste activated sludge extracts (WASE) under different temperature conditions were investigated. The highest lipid content (59.13%) and lipid productivity (80.41 mg L-1 d-1) were obtained at cultivation temperatures of 10 and 25 °C, respectively. It was found that microalgae can effectively utilize TN/TP/NH4+-N and other nutrients of WASE. The highest utilization rates of TP, TN and NH4+-N were achieved at a cultivation temperature of 10 °C, reaching 84.97, 77.49 and 92.32%, respectively. The algal fatty acids had carbon chains predominantly ranging from C14 to C18, making them suitable for biodiesel production. Additionally, a comprehensive analysis of transcriptomics and metabolomics revealed up-regulation of genes associated with triglyceride assembly, the antioxidant system of algal cells, and cellular autophagy, as well as the accumulation of metabolites related to the tricarboxylic acid (TCA) cycle and lipids. This study offers novel insights into the microscopic mechanisms of microalgae culture using WASE and approaches for the resource utilization of sludge.

New insights into rare earth element-induced microalgae lipid accumulation: Implication for biodiesel production and adsorption mechanism.

A coupling technology for lipid production and adsorption of rare earth elements (REEs) using microalgae was studied in this work. The microalgae cell growth, lipid production, biochemical parameters and lipid profiles were investigated under different REEs (Ce3+, Gd3+and La3+). The results showed that the maximum lipid production was achieved at different concentrations of REEs, with lipid productivities of 300.44, 386.84 and 292.19 mg L-1 d-1 under treatment conditions of 100 µg L-1 Ce3+, 250 µg L-1 Gd3+ and 1 mg L-1 La3+, respectively. Moreover, the adsorption efficiency of Ce3+, Gd3+ and La3+exceeded 96.58 %, 93.06 % and 91.3 % at concentrations of 25-1000 µg L-1, 100-500 µg L-1 and 0.25-1 mg L-1, respectively. In addition, algal cells were able to adsorb 66.2 % of 100 µg L-1 Ce3+, 48.4 % of 250 µg L-1 Gd3+ and 59.9 % of 1 mg L-1 La3+. The combination of extracellular polysaccharide and algal cell wall could adsorb 25.2 % of 100 µg L-1 Ce3+, 44.5 % of 250 µg L-1 Gd3+ and 30.5 % of 1 mg L-1 La3+, respectively. These findings indicated that microalgae predominantly adsorbed REEs through the intracellular pathway. This study elucidates the mechanism of effective lipid accumulation and adsorption of REEs by microalgae under REEs stress conditions. It establishes a theoretical foundation for the efficient microalgae lipid production and REEs recovery from wastewater or waste residues containing REEs.

Histological and single-nucleus transcriptome analyses reveal the specialized functions of ligular sclerenchyma cells and key regulators of leaf angle in maize.

Leaf angle (LA) is a crucial factor that affects planting density and yield in maize. However, the regulatory mechanisms underlying LA formation remain largely unknown. In this study, we performed a comparative histological analysis of the ligular region across various maize inbred lines and revealed that LA is significantly influenced by a two-step regulatory process involving initial cell elongation followed by subsequent lignification in the ligular adaxial sclerenchyma cells (SCs). Subsequently, we performed both bulk and single-nucleus RNA sequencing, generated a comprehensive transcriptomic atlas of the ligular region, and identified numerous genes enriched in the hypodermal cells that may influence their specialization into SCs. Furthermore, we functionally characterized two genes encoding atypical basic-helix-loop-helix (bHLH) transcription factors, bHLH30 and its homolog bHLH155, which are highly expressed in the elongated adaxial cells. Genetic analyses revealed that bHLH30 and bHLH155 positively regulate LA expansion, and molecular experiments demonstrated their ability to activate the transcription of genes involved in cell elongation and lignification of SCs. These findings highlight the specialized functions of ligular adaxial SCs in LA regulation by restricting further extension of ligular cells and enhancing mechanical strength. The transcriptomic atlas of the ligular region at single-nucleus resolution not only deepens our understanding of LA regulation but also enables identification of numerous potential targets for optimizing plant architecture in modern maize breeding.

Phytochrome B interacts with LIGULELESS1 to control plant architecture and density tolerance in maize.

Over the past few decades, significant improvements in maize yield have been largely attributed to increased plant density of upright hybrid varieties rather than increased yield per plant. However, dense planting triggers shade avoidance responses (SAR) that optimize light absorption but impair plant vigor and performance, limiting yield improvement through increasing plant density. In this study, we demonstrated that high-density induced leaf angle narrowing and stem/stalk elongation are largely dependent on phytochrome B (phyB1/B2), the primary photoreceptor responsible for perceiving red (R) and far-red (FR) light in maize. Maize phyB physically interacts with the LIGULELESS1 (LG1), a classical key regulator of leaf angle, to coordinately regulate plant architecture and density tolerance. The abundance of LG1 is significantly increased by phyB under high R:FR light (low density) but rapidly decreases under low R:FR light (high density), correlating with variations in leaf angle and plant height under various densities. Additionally, we identified the homeobox transcription factor HB53 as a target co-repressed by both phyB and LG1 but rapidly induced by canopy shade, indicating its central role in response to varying densities. Notably, HB53 regulates plant architecture by controlling the elongation and division of ligular adaxial and abaxial cells. These findings uncover the phyB-LG1-HB53 regulatory module as a key molecular mechanism governing plant architecture and density tolerance, providing potential genetic targets for breeding maize hybrid varieties optimized for high-density planting.

Accelerated reduction of chlorinated nitroaromatic antibiotic chloramphenicol by biocathode.

Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a priority pollutant in wastewaters. A fed-batch bioelectrochemical system (BES) with biocathode with applied voltage of 0.5 V (served as extracellular electron donor) and glucose as intracellular electron donor was applied to reduce CAP to amine product (AMCl2). The biocathode BES converted 87.1 ± 4.2% of 32 mg/L CAP in 4 h, and the removal efficiency reached 96.0 ± 0.9% within 24 h. Conversely, the removal efficiency of CAP in BES with an abiotic cathode was only 73.0 ± 3.2% after 24 h. When the biocathode was disconnected (no electrochemical reaction but in the presence of microbial activities), the CAP removal rate was dropped to 62.0% of that with biocathode BES. Acetylation of one hydroxyl of CAP was noted exclusive in the biocatalyzed process, while toxic intermediates, hydroxylamino (HOAM), and nitroso (NO), from CAP reduction were observed only in the abiotic cathode BES. Electrochemical hydrodechlorination and dehalogenase were responsible for dechlorination of AMCl2 to AMCl in abiotic and microbial cathode BES, respectively. The cyclic voltammetry (CV) highlighted higher peak currents and lower overpotentials for CAP reduction at the biocathode compared with abiotic cathode. With the biocathode BES, antibacterial activity of CAP was completely removed and nitro group reduction combined with dechlorination reaction enhanced detoxication efficiency of CAP. The CAP cathodic transformation pathway was proposed based on intermediates analysis. Bacterial community analysis indicated that the dominate bacteria on the biocathode were belonging to α, ß, and γ-Proteobacteria. The biocathode BES could serve as a potential treatment process for CAP-containing wastewater.

Improving the short-chain fatty acids production of waste activated sludge stimulated by a bi-frequency ultrasonic pretreatment.

Short-chain fatty acids (SCFAs) are the most important intermediate in the waste activated sludge (WAS) fermentation process. This work explored a novel approach to improve the SCFAs production from WAS. Experimental results showed that the disintegration and acidification of WAS were enhanced markedly by using bi-frequency (28+40 kHz) ultrasonic pretreatment compared with monofrequency (28 kHz and 40 kHz) ultrasonic pretreatments. After 28 + 40 kHz ultrasonic pretreatment, the SCOD concentration increased from original 363 mg COD l(-1) to 10810 mg COD l(-1) which was 1.53-fold and 1.44-fold of the values obtained with 28kHz and 40kHz ultrasonic pretreatments, respectively. The maximum SCFAs production reached 7587 mg COD l(-1) in the 28 + 40 kHz test which was respectively 1.25-fold and 1.31-fold of that in the 28 kHz (6053 mg COD l(-1)) and 40 kHz (5809 mg COD I(-1)) tests. This was the highest SCFAs production obtained so far using WAS, pretreated by ultrasonic technology, as the renewable carbon source. SCFAs composition analysis revealed there was more acetic acid (3992 mg COD l(-1), accounted for 52.6% of the total SCFAs) for the 28+40 kHz ultrasonic pretreatment which was beneficial to many subsequent bioprocesses.

Lipid production characteristics of a newly isolated microalga Asterarcys quadricellulare R-56 as biodiesel feedstock.

In this study, a new microalgal strain, Asterarcys quadricellulare R-56, was isolated for biomass and lipid production. The effects of carbon and nitrogen sources and initial pH on the cell growth and lipid accumulation of strain R-56 were investigated. At 10 g L-1 glucose, 0.6 g L-1 sodium nitrate, and pH 7, the highest biomass of 4.18 g L-1 and lipid content of 43.66% were obtained. Microalgae had a broad pH tolerance in the range of 5-11, and the pH of the culture medium was close to neutral at the end of cultivation. The maximum contents of chlorophyll, carbohydrate, and protein under the recommended culture conditions were 19.47 mg mL-1, 21.80%, and 29.94%, respectively. Palmitic and palmitoleic acid contents in strain R-56 accounted for as high as 83.73% of total fatty acids. This study suggested that strain R-56 was a promising lipid producer for high-quality biodiesel production.