Improving the growth of Spirulina in CO2 absorption and microalgae conversion (CAMC) system through mixotrophic cultivation: Reveal of metabolomics

Dissecting the mechanism of synergistic interactions between Aspergillus fumigatus and the microalgae Synechocystis sp. PCC6803 under Cd(II) exposure: insights from untargeted metabolomics

Co-culturing fungi and microalgae may effectively remediate wastewater containing Cd and harvest microalgae. Nevertheless, a detailed study of the mechanisms underlying the synergistic interactions between fungi and microalgae under Cd(II) exposure is lacking. In this study, Cd(II) exposure resulted in a significant enhancement of antioxidants, such as glutathione (GSH), malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide dismutase (SOD) compared to the control group, suggesting that the cellular antioxidant defense response was activated. Extracellular proteins and extracellular polysaccharides of the symbiotic system were increased by 60.61 % and ,24.29 %, respectively, after Cd(II) exposure for 72 h. The adsorption behavior of Cd(II) was investigated using three-dimensional fluorescence excitation-emission matrix (3D-EEM), fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Metabolomics results showed that the TCA cycle provided effective material and energy supply for the symbiotic system to resist the toxicity of Cd(II); Proline, histidine, and glutamine strengthened the synergistic adsorption capacity of the fungus and microalgae. Overall, the theoretical foundation for a deep comprehension of the beneficial interactions between fungi and microalgae under Cd(II) exposure and the role of the fungal-algal symbiotic system in the management of heavy metal pollution is provided by this combined physiological and metabolomic investigation.

Stable isotope labeling and functional gene prediction elucidate the carbon metabolism in fermentative bacteria and microalgae coupling system

The application of the fermentative bacteria and microalgae coupling system in the wastewater treatment has been studied, but there remains few knowledge regarding the organic and inorganic carbon metabolism within this system. In this study, the carbon metabolism of microalgae and fermentative bacteria was elucidated by 13C stable isotope labeling and functional gene prediction, respectively. The 13C glucose and 13C NaHCO3 were used as stable isotope tracers to clarify the organic and inorganic carbon metabolism of microalgae, indicating that approximately 71.5 % of the Acetyl-CoA in microalgae was synthesized from organic carbon sources, while 26.8 % was synthesized through the utilization of inorganic carbon sources. Inorganic carbon sources can enhance the activity of photosynthetic system and facilitate the Calvin cycle. Considering the adequate organic carbon sources and insufficient inorganic carbon sources in the fermentative bacteria and microalgae coupling system, NaHCO3 was added to improve carbon utilization of microalgae. The maximum microalgal lipid yield reached 1130.37 mg/L with 1000 mg/L NaHCO3 supplementation. Functional gene prediction was used to analysis the effect of various carbon composition on the bacterial carbon metabolism. Notably, the additional inorganic carbon sources increased the abundance of bacterial functional genes associated with the fermentation and acetic acids synthesis, which was advantageous for VFAs production and further promoted microalgae growth. This study can gain a deeper understanding of microbial metabolic mechanisms during the operation of fermentative bacteria and microalgae system, and improve its sustained operational stability.

An assessment of the autotrophic/heterotrophic synergism in microalgae under mixotrophic mode and its contribution in high-rate phosphate recovery from wastewater

Dual carbon metabolisms and the synergism contribute to improving nutrient recovery under mixotrophy. However, how synergism influences nutrient recovery has yet to be understood, which is revealed in the current study. Due to dual carbon metabolisms and synergism,the PO4--P recovery rate under mixotrophy reached 0.34 mg L-1 h-1. Due to the internal cycling of respiratory CO2, the mutualistic index (MI) in terms of synergism helped Scenedesmus accumulate 27.49 % more biomass under mixotrophy than sum of the two controls. In contrast, MI contributed 0.26 g L-1 d-1 to the total modeled mixotrophic productivity of 1.15 g L-1 d-1. To total modeled PO4--P recovery, mixotrophic-auto, and mixotrophic-hetero shares were 42 % and 58 %. The synergism under mixotrophy contributed 20 % in total PO4--P recovery. The PO4--P recovery rate under mixotrophywas comparable to other biological P removal methods. These findings emphasize the potential of synergism in improving productivityand promoting resource recovery for sustainable wastewater treatment.

Effect of phytohormones on the carbon sequestration performance of CO2 absorption-microalgae conversion system under low light restriction

Microalgae have the potential to fix CO2 into valuable compounds. Low photosynthetic efficiency caused by low light was one of the challenges faced by microalgae carbon sequestration. In this study, Melatonin (MT) and indole-propionic acid (IPA) were used to alleviate the growth inhibition of Spirulina in CAMC system under low light restriction. The results showed that MT and IPA increased biomass and carbon fixation capacity. 10 mg/L IPA group achieved the maximum biomass and carbon fixation capacity, which were 17.11% and 21.46% higher than control. MT and IPA promoted the synthesis of chlorophyll, which in turn captured more light energy for microalgae growth. The increase of superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) activities enhanced the resistance of microalgae to low light stress. MT and IPA promoted the secretion of extracellular polymeric substances (EPS) which was benefit to protect cells. The maximum phycocyanin content and yield was found in 10 mg-IPA group, which was 20.67% and 46.67% higher than control. MT and IPA improved the synthesis of carbohydrates and proteins and increased carbohydrates and proteins yield. This indicated that adding phytohormones was an effective method to alleviate the growth of microalgae restricted by low light stress, which provided a theoretical guidance for the application of CAMC system in CO2 capture and resource utilization.

Enhancing CO2 fixation by microalgae in a Photobioreactor: Molecular mechanisms with exogenous carbonic anhydrase

Microalgae biotechnology holds great potential for mitigating CO2 emissions, yet faces challenges in commercialization due to suboptimal photosynthetic efficiency. This study presents an innovative approach to improve CO2 mass transfer efficiency in microalgae using carbonic anhydrase (CA) in an internal LED flexible air-lift photobioreactor. Optimal conditions initial inoculation with 3.55 × 106 cells/mL and 20 % CO2 concentration, complemented by white LED lighting in Chlorella sp. CA regulated intracellular composition, enhancing chlorophyll, lipid, and protein contents. Metabolomics revealed elevated malic and succinic acids, associated with increased Ribulose 1,5-bisphosphate carboxylase oxygenase (RuBisCO) and Acetoacetyl coenzyme A (Acetyl-CoA) activities, facilitating efficient carbon fixation. CA also mitigated cellular oxidative stress by reducing reactive oxygen species (ROS). Furthermore, CA improved extracellular electron acceptor with currents surpassed CK. This CA-based microalgae biotechnology provides a foundation for future commercial applications, addressing CO2 emissions.

The Effecting Mechanisms of 100 nm Sized Polystyrene Nanoplastics on the Typical Coastal Alexandrium tamarense

Due to the increase in nanoplastics (NPs) abundance in aquatic environments, their effects on phytoplankton have aroused large research attention. In this study, 100 nm sized polystyrene NPs were chosen to investigate their effecting performance and mechanisms on a typical dinoflagellates Alexandrium tamarense. The results indicated the population growth and photosynthetic efficiencies of A. tamarense were significantly inhibited by NPs exposure, as well as the increase in cellular total carotenoids and paralytic shellfish toxins (PSTs). Meanwhile, the cellar ROS levels increased, corresponding to the increased activities or contents of multiple antioxidant components, including SOD, CAT, GPX, GR, GSH and GSSG. The transcriptional results support the physiological-biochemical results and further revealed the down-regulation of genes encoding the light reaction centers (PSI and PSII) and up-regulation of genes encoding the antioxidant components. Up-regulation of genes encoding key enzymes of the Calvin cycle and glycolytic pathway together with the TCA cycle could accelerate organic carbon and ATP production for A. tamarense cells resistant to NPs stress. Finally, more Glu and acetyl-CoA produced by the enhanced GSH cycle and the glycolytic pathway, respectively, accompanied by the up-regulation of Glu and Arg biosynthesis genes supported the increase in the PST contents under NPs exposure. This study established a data set involving physiological-biochemical changes and gene information about marine dinoflagellates responding to NPs, providing a data basis for further evaluating the ecological risk of NPs in marine environments.

Treatment of agricultural wastewater using microalgae: A review

The rapid development of agriculture has led to a large amount of wastewater, which poses a great threat to environmental safety. Microalgae, with diverse species, nutritional modes and cellular status, can adapt well in agricultural wastewater and absorb nutrients and remove pollutants effectively. Besides, after treatment of agricultural wastewater, the accumulated biomass of microalgae has broad applications, such as fertilizer and animal feed. This paper reviewed the current progresses and further perspectives of microalgae-based agricultural wastewater treatment. The characteristics of agricultural wastewater have been firstly introduced; Then the microalgal strains, cultivation modes, cellular status, contaminant metabolism, cultivation systems and biomass applications of microalgae for wastewater treatment have been summarized; At last, the bottlenecks in the development of the microalgae treatment methods, as well as recommendations for optimizing the adaptability of microalgae to wastewater in terms of wastewater pretreatment, microalgae breeding, and microalgae-bacterial symbiosis systems were discussed. This review would provide references for the future developments of microalgae-based agricultural wastewater treatment.

Utilizing fish wastewater in aquaponic systems to enhance anti-inflammatory and antioxidant bioactive compounds in Sarcodia suae

Aquaculture wastewater, rich in organic nutrients, is an essential environmental factor. When applied to seaweed cultivation systems, this wastewater holds the potential to notably increase the growth rate and carbon capture of Sarcodia suae. Sarcodia suae has the potential to be a healthy food due to its various biological activities; however, its chemical composition has yet to be completely defined. In this study, we applied a UHPLC-HRMS-based foodomics strategy to determine and classify possible bioactive metabolites in S. suae. From pooled seaweed samples (S. suae cultured in filtered running, FR, aquaponic recirculation, AR systems), we identified 179 and 146 compounds in POS and NEG modes, respectively. These compounds were then classified based on their structures using the Classyfire classification. Results show that S. suae in AR exhibited higher growth performance, and ten upregulated metabolites were determined. We also validated the anti-inflammatory and antioxidative bioactivities of some selected compounds. Our study provided important insights into the potential use of fish wastewater in aquaponic systems to profile and produce bioactive compounds in S. suae comprehensively. This has significant implications for the development of sustainable food and the promotion of environmental health.

Insight into the potential mechanism of bicarbonate assimilation promoted by mixotrophic in CO2 absorption and microalgae conversion system

CO2 absorption-microalgae conversion (CAMC) system is a promising carbon capture and utilization technology. However, the use of HCO3- as a carbon source often led to a slower growth rate of microalgae, which also limited the application of CAMC system. In this study, the assimilation efficiency of HCO3- in CAMC system was improved through mixotrophic, and the potential mechanism was investigated. The HCO3- assimilation efficiency and biomass under mixotrophic were 34.79% and 31.76% higher than that of control. Mixotrophic increased chlorophyll and phycocyanin content, which were beneficial to capture more light energy. The content of ATP and NADPH reached 566.86 μmol/gprot and 672.86 nmol/mgprot, which increased by 31.83% and 27.67% compared to autotrophic. The activity of carbonic anhydrase and Rubisco increased by 18.52% and 22.08%, respectively. Transcriptome showed that genes related to photosynthetic and respiratory electron transport were up-regulated. The synergy of photophosphorylation and oxidative phosphorylation greatly improved energy metabolism efficiency, thus accelerating the assimilation of HCO3-. These results revealed a potential mechanism of promoting the HCO3- assimilation under mixotrophic, it also provided a guidance for using CAMC system to serve carbon neutrality.

Biomanufacturing of γ-linolenic acid-enriched galactosyldiacylglycerols: Challenges in microalgae and potential in oleaginous yeasts

γ-Linolenic acid-enriched galactosyldiacylglycerols (GDGs-GLA), as the natural form of γ-linolenic acid in microalgae, have a range of functional activities, including anti-inflammatory, antioxidant, and anti-allergic properties. The low abundance of microalgae and the structural stereoselectivity complexity impede microalgae extraction or chemical synthesis, resulting in a lack of supply of GDGs-GLA with a growing demand. At present, there is a growing interest in engineering oleaginous yeasts for mass production of GDGs-GLA based on their ability to utilize a variety of hydrophobic substrates and a high metabolic flux toward fatty acid and lipid (triacylglycerol, TAG) production. Here, we first introduce the GDGs-GLA biosynthetic pathway in microalgae and challenges in the engineering of the native host. Subsequently, we describe in detail the applications of oleaginous yeasts with Yarrowia lipolytica as the representative for GDGs-GLA biosynthesis, including the development of synthetic biology parts, gene editing tools, and metabolic engineering of lipid biosynthesis. Finally, we discuss the development trend of GDGs-GLA biosynthesis in Y. lipolytica.

Lutein production from microalgae: A review

Lutein production from microalgae is a sustainable and economical strategy to offer the increasing global demands, but is still challenged with low lutein content at the high-cell density for commercial production. This review summarizes the suitable conditions for cell growth and lutein accumulation, and presents recent cultivation strategies to further improve lutein productivity. Light and nitrogen play critical roles in lutein biosynthesis that lead to the efficient multi-stage cultivation by increasing lutein content at the later stage. In addition, metabolic and genetic designs for carbon regulation and lutein biosynthesis are discussed at the molecule level. The in-situ lutein accumulation in fermenters by regulating carbon metabolism is considered as a cost-effective direction. Then, downstream processes are summarized for the efficient lutein recovery. Finally, challenges of current lutein production from microalgae are discussed. Meanwhile, potential solutions are proposed to improve lutein content and drive down costs of microalgal biomass.